Field of the Invention

The present invention relates to a novel class of molecule and applications therefor.

The invention has been developed primarily for use in temperature tracing or probing and electronic switching apparatus and will be described hereinafter with reference to these applications. However, it will be appreciated that the invention is not limited to these particular fields of use.

Background of the Invention

Electronic memory and switching devices including transistor based processing units have been able to be reduced in size significantly in the last 40 years. In the field of semiconductor device fabrication, the process used to create the integrated circuits in common electronic devices have been decreasing the minimum size of feature widths from about 10 pm in the early l970s to 1000 times smaller at almost 10 nm currently. It is envisaged between 3-7 nm features will be commonly used in commercial devices in the near future.

However, fabrication of electronic imputing devices with feature widths in the low nanometres introduces undesirable quantum effects, for example, making it relatively difficult to reliably produce electronics at such scales. Alternative methods are always being considered whether these be conventional solid-state-type electronics or those including organic compounds.

Genesis of the Invention

The genesis of the invention is a desire to provide a novel class of molecules for use in temperature tracing and/or electronic switching applications that ameliorates one or more of the disadvantages of the prior art, or to provide a useful alternative.

Summary of the Invention

In accordance with a first aspect of the present invention there is disclosed a molecule configured to be selectively switched between different configurations, the molecule comprising: a macrocycle having a cyclic ordering in a set or subset of bonds and having an inner ring structure;

a bridging structure including at least three atoms or sub-structures wherein the bridging structure is constrained by the macrocycle inner ring structure and includes a net electric dipole switchable between at least two configurations;

a plurality of spaced apart macrocycle adjuncts adapted to sterically allow and to provide steric protection of the bridging structure in each of the at least two configurations.

In accordance with a second aspect of the present invention there is disclosed a memory element comprising one or more molecules according to the first aspect of the invention disposed intermediate upper and lower conductive elements, the conductive elements having electrical contacts adapted to change and/or probe the configuration of the bridging structure(s).

According to another aspect of the present invention there is provided a electret microphone comprising:

one or molecules according to the first aspect of the invention, the molecule disposed intermediate a pair of electrical contacts wherein one said contact is connected to ground and the other contact in electrical communication with the base of a field-effect transistor wherein the emitter is connect to ground and the collector in electrical communication with an external voltage source for output via a series polarized capacitor such that vibration of the molecule in response to a noise provides an amplified microphone output.

Preferred embodiments and examples of the invention will now be described, by way of example only, with reference to the following description.

In a first preferred embodiment of the invention there is provided a molecule or molecular specie that includes a macrocycle structure (the macrocycle) and a constrained invertible dipole structure (the invertible dipole); the latter being a structure that is constrained by the macrocycle, that tends to exhibit a net electric dipole, and that can invert or be inverted (or switched or transitioned) between two configurations or conformations that each correspond to an isomer or conformer of the molecule or molecular specie (the first and second isomers or conformers, respectively).

Brief Description of the Drawings

Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Fig. 1 show representations of some example structures and parent structures thereof of the macrocycle of the molecule or molecular specie according to a preferred embodiment of the invention;

Fig. 2 shows a representation of first and second isomers or conformers of the molecule or molecular specie according to a preferred embodiment of the invention; Fig. 3 shows a representation of the vector component of the overall net electric dipole m of a first and second of the molecule or molecular specie according to the preferred embodiment;

Fig. 4 show representations of the relationship between the bond angle inversion and the asymmetry and relatedly the vector component of the overall net electric dipole m for some selections of the invertible dipole of molecules according to preferred embodiments of the invention;

Fig. 5 shows a representation of preferred structures/configurations for the macrocycle adjuncts of the invertible-dipole-in-a-box molecule according to a preferred embodiment of the invention;

Fig. 6 shows a representation of the box in the invertible-dipole-in-a-box of the molecule or molecular specie provided as a B ₂ OF ₂ -me,sO-tetradurylporphyrin according to a preferred embodiment of the invention;

Fig. 7 shows a representation of preferred structure(s) of the box for the invertible dipole-in-a-box, more preferably when the molecule or molecular specie is a porphyrin or porphyinoid;

Fig. 8 shows a representation of the means for translational and rotational constraints, when the molecule or molecular specie according to the preferred embodiment is provided as a B ₂ OF ₂ -tetraarylporphyrin;

Fig. 9 shows a representation of the means for translational and rotational constraints, and in particular the reactive groups, when the molecule or molecular specie is provided as a B ₂ OF ₂ -hexaaryl-dioxaporphyrin; Fig. 10 is an example circuit for manipulating and/or interrogating a state of a memory cell or device made using the molecule or molecular specie according to the preferred embodiments of the invention;

Fig. 11 is an example circuit for an element that exploits the ferroelectric -like property of the molecule or molecular specie according to preferred embodiments of the invention; and

Figs. 12 to 28 show representations of molecules or molecular species according to preferred embodiments of the invention;

Detailed Description

The invertible dipole

The invertible dipole according to preferred embodiments includes three atoms or structures abbreviated as X _b , X _c , X _d as can be seen in Fig. 2 for example. The invertible dipole preferably includes at least one other, and more preferably two other, atoms or structures abbreviated as X _a , X _e . At least one pair of the atoms or structures X _a , X _b , X _c , X _d , X _e constitutes (or comprises) a polar group or polar structure or polar moiety. Preferably one of (and more preferably both of) X _a (if so included) when in combination with X _b , and X _e (if so included) when in combination with X _d , constitutes (or comprises) the polar group or structure or moiety. The atoms or structures of the invertible dipole (as included) are bonded sequentially in the order: X _a , X _b , X _c , X _d , X _e - The‘X’ in the above abbreviations is not a symbol for a halogen (but could be a halogen, e.g. as described below).

The atoms or structures of the invertible dipole are preferably selected from the following sets:

X _c e {CH ₂ , NH, N , O, S, Se, Te}.

X _b , X _d e {Be, B, C, N, Al, Si, P, S, Ge, Ga, As, Se, Sn, In, Te, 4-coordinate transition metals } .

X _a , X _e e {B(Gl7) ₃ , BR ₃ , CR ₃ , NR ₂ , NR ₃ , OR, O , F, PR ₂ , PR ₃ , SR, S , Cl}; where R is preferably an aliphatic or aromatic moiety, more preferably R e jH, alkyl, or aryl}, and G17 = a halogen.

More preferably, the atoms or structures X _a , X _b , X _c , X _d , X _e are selected in

corresponding order from the following set:

X _a X _b X _c X _d X _e e {FBOBF, FCOCF, FSiOSiF, OPOPO}

Preferably, the invertible dipole is a l,3-difluoro-^ ⁴ ^ ⁴ -diboroxan-l,l,3,3-tetrayl group (said differently, a B(F)OB(F) or B ₂ OF ₂ ).

The macrocycle

The macrocycle has cyclic ordering in a set or subset of bonds as seen for example in Fig. 1. Preferably, the macrocycle has cyclic ordering in more than one set or subset of bonds.

Preferably, the macrocycle is aromatic, and more preferably substantially extensively conjugated. Preferably, the cyclically-ordered (sub)set(s) of bonds involves or includes at least one set of delocalised pi-electrons or pi-bond conjugations. More preferably, at least one of the set(s) of delocalised pi-electrons or pi-bond

conjugations is/are cyclically continuous (e.g. as in porphyrin, as opposed to corrin, the latter being able to provide a less preferred but amenable rigidity through a near- completely cyclic conjugation). Preferably, at least one of the set(s) of cyclically continuous delocalised pi-electrons or pi-bond conjugations encircles or surrounds the invertible dipole. Preferably, the macrocycle is planar or substantially planar (forming a plane of the macrocycle).

Preferably, the macrocycle is of low polarity or substantially low polarity. Preferably, the macrocycle is substantially rigid and/or shape-invariant toward the invertible dipole, or between different states or configurations of the invertible dipole, (or between all isomers or conformers of the molecule or molecular specie, in particular the first and second isomers or conformers). Preferably, the macrocycle has a polydentate or multidentate ligand structure, in that the macrocycle can form a plurality of bonds with another molecule or structure disposed therein (or therewith). Preferably, the macrocycle is tetradentate (K ⁴ ), pentadentate (K ), hexadentate (K ), heptadentate (K ), octadentate (K ), or larger (K ), but most preferably tetradentate (K ⁴ ).

Preferably, the polydentate or multidentate ligand structure is formed (at least in part but preferably substantially or entirely) from a plurality of homocyclic or heterocyclic organic ring structures. Preferably, the heterocyclic organic ring structures are selected from the class consisting of five-membered ring structures, six-membered ring structures (e.g. pyridine), and five-membered ring structures adjoining six- membered ring structures (e.g. isoindole; such adjoining ring structures not being mutually exclusive ring structures). Preferably, the parent structure of the macrocycle (being the parent structure less‘the macrocycle adjuncts’ as introduced later, in particular) is formed from pyrrole or pyrrole-like sub-units (e.g. pyrroline), but most preferably from pyrrole sub-units.

Preferably, the heterocyclic organic ring structures (or the atoms or structures X _f , X _g , X _h , and X as later introduced) are bonded together via linker atoms selected from the class consisting of C, N, O, and S. More preferably, two pairs of adjacent ones of the heterocyclic organic ring structures (or of the atoms or structures X _f , X _g , X _h , and X as later introduced; such pairs not being mutually exclusive pairs) are bonded together via N ones of the linker atoms and another two such pairs are bonded together via ones of the linker atoms selected from the class consisting of O and S. Even more preferably, two such pairs are bonded together via C ones of the linker atoms and another two such pairs are bonded together via ones of the linker atoms selected from the class consisting of N, O, and S. Most preferably, all such pairs are bonded together via C ones of the linker atoms, or all such pairs are bonded together via N ones of the linker atoms. In an alternative preference, the heterocyclic organic ring structures (or the atoms or structures X _f , X _g , X , and X as later introduced) are bonded together via linker structures that are selected to be rigid or substantially rigid and that do not exceed 8 atoms in a contiguous order of linker bonds between each (i.e. every) pair of adjacent ones of the heterocyclic organic ring structures (or of the atoms or structures X _f , X _g , X _h , and Xf as later introduced; such pairs not being mutually exclusive pairs). In another preference, two pairs of adjacent ones of the heterocyclic organic ring structures (such pairs not being mutually exclusive pairs) are bonded together directly and another two such pairs are bonded together via conjugated ethylene moieties or via CC moieties that share delocalised pi-electrons.

Preferably, the parent structure of the macrocycle is a porphin or porphine. Preferably, the macrocycle is a porphyrin or porphyrinoid (e.g. a benzoporphyrin, dihomoporphyrin, 5,l5-diazaporphyrin, or porphyrazine), or another macrocyclic ligand substantially related thereto (e.g. an isoporphyrin, porphycene, pyrphyrin, corrole, chlorin, bacteriochlorin, isobacteriochlorin, corphin, or corrin, porphyrazine homologues such pthalocyanines). Most preferably, the macrocycle is a porphyrin or porphyrinoid or a homologue thereof.

Depending upon the selection of constituent atoms or structures, the macrocycle of the molecule or molecular specie of preferred embodiments of the invention can

(advantageously) have the structure(s) (or parent structure(s) thereof) as illustrated in Figure 1 which provides representations of some preferred example structure(s) (and parent structure(s) thereof) of the macrocycle of the molecule or molecular specie of the preferred embodiment of the invention. A stick format is used with non-carbon atoms as indicated (some parent structure hydrides or substitutable hydrides of certain non-carbon atoms are also indicated). As can be seen, the structure(s) are extensively conjugated. The first illustrated macrocycle (Ml) is a porphyrin, the next illustrated macrocycles (M2-M10) are porphyrinoids, and the remaining illustrated macrocycles (M10-M14; M16) are other macrocyclic ligands substantially related thereto. M15 is an example of a higher-order one of the polydentate or multidentate ligand structure.

The macrocycle includes at least four atoms or structures for bonding to the invertible dipole, abbreviated as X _f , X _g , X _h, and X^ Preferably, the atoms or structures X _f , X _g ,

X _h, and Xi form or substantially form a plane. Preferably, the atoms or structures X _f , X _g , X _h , and Xi are coplanar or substantially coplanar with the plane of the macrocycle.

Preferably, at least two of, and more preferably each of, the atoms or structures X _f ,

X _g , X _h , and Xi share delocalised pi-electrons with, or exhibit pi-bond conjugation with, or are conjugated as part of, the cyclically-ordered (sub)set(s) of bonds. Most preferably, at least two of, and more preferably each of, the atoms or structures X _f , X _g , X _h , and Xi share delocalised pi-electrons with, or exhibit pi-bond conjugation with, or are conjugated as part of, at least one of the preferred cyclically continuous set(s) of delocalised pi-electrons or pi-bond conjugations.

Preferably, the atoms or structures X _f , X _g , X , and Xi are selected from the set (or are structures that include atoms selected from the set):

X _f , X _g , X _h , X, e {B, C, N, 0, P, S }.

More preferably, the atoms or structures X _f , X _g , X _h , and Xi are selected from the set:

X _f , X _g , X _h , Xi e {C, N, 0} (and even more preferably, two of X _f , X _g , X _h , Xi are N).

Most preferably, the atoms or structures X _f , X _g , X _h , and Xi are all N atoms.

Preferably, the atoms forming the cyclically-ordered (sub)set(s) of bonds are selected from the class consisting of B, C, N, O, P, and S. More preferably, the atoms forming the cyclically-ordered (sub)set(s) of bonds are selected from the class consisting of C, N, O, and S. Most preferably, the atoms forming the cyclically-ordered (sub)set(s) of bonds are selected from the class consisting of C, and N.

Preferably, the remainder of the macrocycle (being comprised of all atoms of the macrocycle other than X _f , X _g , X _h , Xi and‘the macrocycle adjuncts’ as introduced later) is comprised of C and H only, but for any structures to promote tethering or crystallisation (as introduced later). More preferably, the remainder of the macrocycle is comprised of C and H only. However, it will be appreciated that the remainder of the macrocycle can include S, for example, or other low polarity or“non-polar” molecule.

Spatial constraint of the invertible dipole to the macrocycle In each of the first and the second of the isomers or conformers (see Fig. 2): X _b is bonded to X _f and Xi, and X _d is bonded to X _g and X _h . The invertible dipole thereby forms a polar bridge that spans, and/or is accommodated in (or centrally coordinated inside), and/or is encircled by, the macrocycle.

The characteristics of the molecule or molecular specie disclosed thus far can advantageously provide the macrocycle in a form that constrains the invertible dipole (in particular, the configuration or orientation of X _b and X orbitals) so as to restrict the inversion between the two configurations along pathway(s) (referred to hereafter as the inversion pathway(s)) that are associated with a substantial Gibbs free energy barrier (in particular, having regard to energy changes due to thermal and/or inter- molecular interactions that would be deleterious to the later disclosed applications).

Said differently, the first and second isomers or conformers are (or correspond to) substantially distinct/stable molecular states (or classes of closely-related states), and preferably each correspond to local ground states (or substantial ground states) of the molecule or molecular specie, with a (minimum) Gibbs free energy barrier(s) to a reversible transition therebetween (or analogously an activation energy).

Advantageously associated with this (at a molecular level) and relating to the polar group(s) or structure(s) or moiety(s) of the invertible dipole in particular, a first transition (from the first to the second isomer or conformer) is energetically favoured when an externally applied electric field is oriented in a first direction, and a second transition (from the second to the first isomer or conformer) is energetically favoured when the externally applied electric field is oriented in a second direction, the second direction opposing (in part but preferably wholly or substantially) the first direction. Relatedly, the converse relationship applies.

This can occur where, prior to the corresponding first or second transition, the corresponding first or second direction (or vector thereof) is parallel or co-directional (in part but preferably wholly or substantially) with the corresponding molecular dipole moment (or vector thereof) of the corresponding first or second isomer or conformer, whereby the corresponding one of the Gibbs energy barrier(s) to the reversible transition is lower than when the external electric field is not so applied. Or said differently, the vector projection of the corresponding molecular dipole moment onto the vector of the corresponding first or second direction of the externally applied electric field.

For electronic applications in particular, the Gibbs energy barrier(s) to the reversible transition is/are predetermined to be of sufficiently high magnitude to provide a thermal stability against the inversion(s) between the two configurations, and is/are predetermined to be of a sufficiently low magnitude for the externally applied electric field to trigger or mediate or cause the inversion(s).

Preferably, the reversible transition is perfectly reversible. Preferably, the Gibbs energy barrier(s) to the reversible transition is/are between or substantially between 80 and 200 kJ mol ¹ in absence of the externally applied electric field.

The magnitude of the Gibbs energy barrier(s) to the reversible transition can

(advantageously) be predetermined (and relatedly, modelled) largely through the selection of the macrocycle and invertible dipole (and constituent atoms thereof).

The net electric dipole

The characteristics of the molecule or molecular species according to preferred embodiments of the present invention disclosed thus far can also advantageously provide the invertible dipole with the net electric dipole, as referred to previously but discussed hereafter in further detail. The invertible dipole confers a net electric dipole upon (or otherwise influences that of) the molecule or molecular specie (referred to hereafter as the overall net electric dipole ¾_or relatedly the molecular dipole moment).

The atoms or structures of the invertible dipole (as included) that are bonded sequentially in the order X _a , X _b , X _c , X _d , X _e , include a set or subset of atoms that can form a chain of contiguously bonded atoms (hereafter called the bridging atoms) between X _f /Xi and X _g /X _h on the macrocycle. Each of X _b , X _c , and X includes at least one of the bridging atoms. X _c in particular can include atom(s) that is/are not one(s) of the bridging atom(s). Each of X _a and X _e includes at least one atom(s) (hereafter called the bridge-associated atom(s)) that is/are not one(s) of the bridging atom(s) but that is/are bonded to one(s) of the bridging atoms. Preferably, X _c includes only one of the bridging atoms. Preferably, X _b and/or X _d (each) include(s) only one of the bridging atoms. Also preferably only X _b , X _c , and X _d include one(s) of the bridging atoms. The selection of the bridging atoms and other atoms bonded thereto relates to the overall selection of X _a , X _b , X _c , X _d , and X _e .

Depending upon the selection of constituent atoms or structures of the molecule or molecular specie, both the bridging atoms and the bridge-associated atoms (and/or X _a and/or X _e in particular) and the inversion pathway(s) (and energies thereof) can influence the overall net electric dipole m, and the state(s) of the overall net electric dipole m.

At least two of the atoms of the invertible dipole have electronegativities that differ from one another (hereafter called the dipole atoms of differing electronegativity(s)). Preferably, the dipole atoms of differing electronegativity(s) include at least two of the bridging atoms, and preferably include at least one, and more preferably two, of the bridge-associated atoms.

Preferably, one of the bridge-associated atom(s) of X _a has a different electronegativity to the bridging atom(s) of X _b bonded thereto, and more preferably has a greater electronegativity. Preferably, one of the bridge-associated atom(s) of X _e has a different electronegativity to the bridging atom(s) of X _d bonded thereto, and more preferably has a greater electronegativity.

Preferably, one of the bridging atom(s) of X _c has a different electronegativity to the bridging atom(s) of X _b bonded thereto, and more preferably has a greater

electronegativity. Preferably, one of the bridging atom(s) of X _c has a different electronegativity to the bridging atom(s) of X bonded thereto, and more preferably has a greater electronegativity.

In an alternative preference, the electronegativity of one of the bridging atom(s) of X _b is higher than that of the bridge-associated atom(s) of X _a bonded thereto and/or the bridging atom(s) of X _c bonded thereto, and the electronegativity of one of the bridging atom(s) of X is higher than that of the bridge-associated atom(s) of X _e bonded thereto and/or the bridging atom(s) of X _c bonded thereto.

Preferably, the foregoing electronegativity relations are estimated using the Sanderson model or the Mulliken model or the Pauling model of electronegativity.

Preferably, the bridging atoms (and more preferably also the bridge-associated atoms) are selected from the class consisting of period two (or second row) elements on the periodic table, and P, S, and Cl. This selection simplifies synthesis/fabrication and extends device lifetime (in particular for electronic memory applications).

Preferably, the bridging atoms are selected from the class consisting of B and O, and more preferably form an (Gl7)BOB(Gl7)- structure as the invertible dipole (where G17 is a halogen), when in combination with the bridge-associated atoms.

As described previously, the inversion pathway(s) have an association with the Gibbs energy barrier(s) to the reversible transition between the first and second isomers or conformers (or ground states) of the molecule. In particular, the inversion pathway(s) involve an inversion (or partial inversion or substantial inversion) in a bond angle (the inversion being a change in the bond angle, hereafter called the invertible bond angle, that involves angle strain or Baeyer strain in the electron orbitals of the corresponding angularly invertible bonds), the invertible bond angle being formed by at least three of the bridging atoms of X _b , X _c , and X _d . The bond angle inversion contributes to (or preferably substantially determines) the Gibbs energy barrier(s) to the reversible transition.

The bond angle inversion is associated with a corresponding inversion or change in the overall net electric dipole Dm. The dipole change D m arises from the spatial reconfiguration during the bond angle inversion of the dipole atoms of differing electronegativities (preferably those of X _a and/or X _e in particular), and relates in particular to a shift in the mean position of positive and negative partial electric charges associated with the invertible dipole. The characteristics disclosed thus far can advantageously provide the molecule or molecular specie with two substantially distinct/stable states of the overall net electric dipole m, namely a first dipole state and a second dipole state, that correspond in turn to a first and a second of the two configurations of the invertible dipole, and that relatedly correspond to the first and the second of the isomers or conformers (or ground states) of the molecule, respectively. The first dipole state can thus change to the second dipole state through the inversion pathway(s) associated with the Gibbs energy barrier(s) to the reversible transition.

The magnitudes and/or directions of the overall net electric dipoles m of the first and second dipole states can be selected largely through the particular combination of the dipole atoms of differing electronegativities. In particular, there can be selected a difference in magnitude and/or direction of the overall net electric dipole m between the first and second dipole states (and hence there is provided the dipole change dp).

Preferably, the selection of the dipole atoms of differing electronegativities is such that during the inversion between the two configurations, the sign of the component of the overall net electric dipole m (or of the molecular dipole moment) that is perpendicular (strictly speaking‘normal’ but perpendicular is used for convenience) to the plane of the macrocycle (or parallel with the macrocycle axis, as later introduced), is reversed. In an alternative preference, the absolute magnitude of the component of the overall net electric dipole m (or of the molecular dipole moment) that is perpendicular to the plane of the macrocycle (or parallel with the macrocycle axis, as later introduced), undergoes a change or a substantial change.

The constituent atoms or structures of the invertible dipole (and relatedly, the remainder of the macrocycle, and/or the macrocycle adjuncts as later introduced, that are preferably non-polar or substantially non-polar) are preferably selected to confer the overall net electric dipole m with a magnitude of greater than 0.2Debye, more preferably greater than 0.74Debye and most preferably greater than 1-5 Debye in at least one of the first or second isomers or conformers. It will be appreciated, of course, that the overall net electric dipole is arbitrary. Spatial relationships

Depending upon the selection of constituent atoms or structures, the molecule or molecular specie according to preferred embodiments (in particular, the first and second isomers or conformers thereof) can (advantageously) have the

structure(s)/configuration(s) represented in Figure 2. This shows a representation of the first and second isomers or conformers (2a and 2b, respectively) of the molecule or molecular specie according to preferred embodiments.

The macrocycle having the cyclically-ordered (sub)set(s) of bonds is represented as a circle. The invertible dipole, the two configurations thereof, and the bonds between the invertible dipole and the macrocycle, are represented in wedge-and-dash format (and relatedly, in stick format as described below). The wedges are depicted as projecting toward the observer, and the dashes as projecting away from the observer, from the nearest of X _b or X _d (in particular, from the nearest of the bridging atom(s) thereof, or from X _f , X _g , X _h , Xi as further illustrated in Figure 3). Bonds that are (preferably) co-planar or substantially co-planar with the macrocycle (or the plane thereof) are depicted in stick format. Also illustrated is that the reversible transition (or reversible isomerisation or conformerisation) between the first and second isomers or conformers is associated with the Gibbs free energy barrier(s) to each of the first transition (or forward transition of 2a to 2b) and the second transition (or reverse transition of 2b to 2a). As illustrated, the sides of the first isomer or conformer (2a) and the second isomer or conformer (2b) that face toward the observer correspond to ‘the second side’ of the macrocycle as introduced below.

Being substantially planar, the macrocycle has a first side and a second side relative to the atoms or structures X _f , X _g , X _h , and X _f . Said differently, there exists an axis passing through the mean position of the atoms of X _f , X _g , X _h , and Xi (hereafter called the macrocycle axis) that is divided by a least squares mean plane of the atoms of X _f , X _g , X _h , and Xi into the first side and the second side (hereafter called the plane of X _f , X _g , X _h , and Xi), and that is orthogonal to the plane of X _f , X _g , X _h , and X _f .

Preferably, in the first isomer or conformer, the bond vectors from X _b to X _f and Xi, and from X to X _e , extend (or substantially extend) in a direction away from the first side, and the bond vectors from X _b to X _a , and from X _d to X _c , extend (or substantially extend) in a direction away from the second side.

Preferably, in the second isomer or conformer, the bond vectors from X _d to X _g and X _h , and from X _b to X _a , extend (or substantially extend) in a direction away from the second side, and the bond vectors from X _b to X _c , and from X _d to X _e , extend (or substantially extend) in a direction away from the first side.

Preferably, the inversion between the two configurations (and relatedly the first and second transitions) involves the process of‘akamptisomerisation’ as described in Appendix 1. Preferably, each of the first and second isomers or conformers is an akamptisomer.

Depending upon the selection of the dipole atoms of differing electronegativities, the overall net electric dipole m can have a vector component (preferably large in magnitude) that is oriented orthogonal (or substantially orthogonal), or parallel (or substantially parallel), to the plane of the macrocycle (or the plane of X _f , X _g , X _h , and Xi) as represented in Figures 3 and 4 (or relatedly, can a vector component that is an orientation therebetween).

In Fig. 3 there is shown a representation of the vector component of the overall net electric dipole m of a first (3 a) and a second (3b) of the molecule or molecular specie according to preferred embodiments, as arrows. The macrocycles having the cyclically-ordered (sub)set(s) of bonds are represented as circles in a perspective projection. The invertible dipoles are represented in stick format. The bonds between the invertible dipoles and the corresponding macrocycles, are represented in wedge - and-dash format. The wedges are depicted as projecting toward the observer, and the dashes as projecting away from the observer, relative to the atom in the given bond that is nearest the observer. The arrows of the vector components are depicted here in negative-to-positive convention (but depend upon the selection of atoms or structures). Preferably, the vector component of the overall net electric dipole m is aligned (or substantially aligned) parallel to the macrocycle axis in at least one of, and more preferably in each of, the first and second isomers or conformers.

At least one of (and preferably each of) the first and second isomers or conformers is/are preferably asymmetric, and more preferably asymmetric about the macrocycle (or the plane of the macrocycle, or the plane of X _f , X _g , X _h , and Xi). The asymmetry said differently, a first totality of atoms residing on the first side of the macrocycle, do not form a mirror image to a second totality of atoms residing on the second side of the macrocycle (i.e. the first totality is not superimposed over the second totality when reflected about the plane of X _f , X _g , X _h , and Xi).

The asymmetry preferably relates to the spatial position of the bridging atoms of the set {X _b , X _d }, that is comprised of a first subset of the bridging atom(s) of X _b , a second subset of the bridging atom(s) of X _d (hereafter called the first and second sets of asymmetry-associated atom(s), respectively). In particular, in at least one of (and preferably each of) the first and second isomers or conformers, one of the first and second sets of asymmetry-associated atom(s) is preferably‘ ample’ or out-of-plane relative to the plane of the macrocycle, or the plane of X _f , X _g , X _h , and Xi (or ample or out-of-plane relative to the other, as taken relative to the plane of the macrocycle, or the plane of X _f , X _g , X _h , and Xi); whilst the other is‘ parvo’ or in-plane relative to the plane of the macrocycle, or the plane of X _f , X _g , X _h , and Xi (or parvo or in-plane relative to the former, as taken relative to the plane of the macrocycle, or the plane of X _f , X _g , X _h , and Xi). Preferably, the bond angle inversion causes a reversal in this preferred relationship. Reference is made to Appendices 1 to 3 annexed to this description.

For example as illustrated in Figure 3, in the first isomer or conformer the first set of asymmetry-associated atom(s) is amplo and the second set of asymmetry- associated atom(s) is parvo. Subsequent to the bond angle inversion associated with the first transition to the second isomer or conformer, the first set of asymmetry-associated atom(s) is parvo and the second set of asymmetry-associated atom(s) is amplo. Note however that there preferably also exists an inversion symmetry or substantial symmetry between the two configurations. This as defined by a 180° rotation of the invertible dipole about the macrocycle axis, followed by a reflection in the plane of X _f , X _g , X _h , and Xi, followed by the inversion between the two configurations or the bond angle inversion.

The atoms of X _f , X _g , X _h , and Xi that are bonded to the invertible dipole (or the relative spatial positions thereof) are constrained by the macrocycle in a predetermined manner such that the bond angle inversion provides the desired Gibbs energy barrier to the reversible transition (said differently, the bond angle inversion substantially determines the Gibbs energy barrier to the reversible transition, and/or constitutes or characterises the most energetically favourable transition between the first and second isomers or conformers or ground states).

In particular, for spatial configurations of X _f , X _g , X , and Xi that tend to compress (or decrease the angle of) the invertible bond angle (toward higher angular strain or Baeyer strain) in one (or both) of the first and second isomers or conformers or ground states, the macrocycle is preferably rigid or substantially rigid (the rigidity more preferably being in the plane of the macrocycle or in radial direction(s) from the macrocycle axis) throughout the reversible transition (or throughout the first or second transitions or the inversion pathway(s)) such that the bond angle inversion constitutes or characterises the most energetically favourable transition pathway (over all other transitions, e.g. rotation within or rotation of the X _b X _c X _d structure e.g. about the otherwise angularly invertible bond, or rotamerisation of the invertible dipole about the macrocycle axis), and relatedly such that the Gibbs energy barrier(s) to the reversible transition is/are adequately high (e.g. against thermal influences as discussed previously).

Whereas, for spatial configurations of X _f , X _g , X _h , and Xi that tend to extend (or increase the angle of) the invertible bond angle (toward lower angular strain or Baeyer strain; or even further toward a more obtuse angle that provides lower angular strain or Baeyer strain than a ground state or ground orbital configuration of X _c ) in one (or both) of the first and second isomers or conformers or ground states, the macrocycle, whilst preferably being substantially rigid (for reasons discussed in the previous paragraph), preferably also has a degree of flexibility (the flexibility more preferably being in the plane of the macrocycle or in radial direction(s) from the macrocycle axis) throughout the reversible transition (or throughout the first or second transitions or the inversion pathway(s)) such that the Gibbs energy barrier(s) to the reversible transition is/are not excessive, or said differently is/are adequately low (e.g. for manipulation by the externally applied electric field; or for interrogation of a given state of the molecule or molecular specie, or of a material made therefrom, by an electrical device).

It can also be seen from previously described relationships that the invertible dipole has a notional similarity to a transoid bond.

Depending upon the selection of constituent atoms or structures of the molecule or the molecular specie, the overall net electric dipole m can relate to the asymmetry and the bond angle inversion. This is illustrated in Figure 4 (see also Figures 2 and 3 above, related thereto) showing representations of the relationship between the bond angle inversion and the asymmetry (4a); and relatedly the vector component of the overall net electric dipole m for some selections of the invertible dipole (4b). The

representations are illustrated as projections onto a plane that is oriented perpendicular to the plane of the macrocycle or the plane of X _f , X _g , X _h , and Xi (illustrated by a solid line in 4a; horizontal to the page for each of the illustrated invertible dipoles). The invertible dipoles are represented in stick format with the constituent atoms or structures thereof represented either as arbitrary symbols (4a) (‘X’ as used herein does not have any symbolic relationship to previously uses thereof), or as standardised atomic or structural symbols (4b). The atoms or structures X _a , X _b , X _c , X _ci , X _e , are symbolised in (4a) as A, M, X, M, A from left-to-right, generalising a five atom or structure system. The arrows of the vector components are depicted in positive-to- negative convention. The left-hand-side representation of the invertible dipole in (4a) is exemplified with three selections of the invertible dipole in (4b), each

corresponding to one of the first or second isomers or conformers of the molecule or molecular specie according to preferred embodiments.

As illustrated in Figure 4a, the inversion pathway(s) between the two configurations of the invertible dipole involve(s) the inversion of the bond angle formed by the bridging atoms of X _b , X _c , and X _d . Relatedly, the inversion pathway(s) also involve(s) a transitional state or configuration of the invertible dipole (Figure 4a) that has angle strain or Baeyer strain in the angularly invertible bonds, and is thereby associated with the Gibbs energy barrier to the reversible transition.

Preferably, the invertible bond angle approaches, or more preferably substantially equals, or most preferably equals, 180° during the bond angle inversion, or when the molecule or molecular specie is in the transitional state of the invertible dipole (the distinction between these preferences is not clearly seen in Figure 4).

As illustrated in Figure 4b, the molecule or molecular specie can exhibit either a substantially c-axis oriented (substantially parallel to the macrocycle axis) or a substantially a-axis oriented (substantially parallel to the plane of the macrocycle or orthogonal to the macrocycle axis) configuration of the vector of the overall net electric dipole m (relative to the principal axes of the macrocycle).

In general terms, a maximum absolute magnitude of the overall net electric dipole m between one of the first or second dipole states is preferably aligned either parallel or substantially parallel to the macrocycle axis, or orthogonal or substantially orthogonal to the macrocycle axis, but more preferably either parallel or substantially parallel to the macrocycle axis.

Steric effects

As evident from (and inherent to) the characteristics disclosed thus far, the molecule or molecular specie according to preferred embodiments is capable of existing at different times in each of the two configurations of the invertible dipole, or relatedly in each of the first and second isomers or conformers or ground states or closely related classes of states thereof (referred to hereafter as the two-state capability).

The molecule or molecular specie also has the previously described energetic and state transition characteristics, in particular: the inversion pathways, the bond angle inversion, the reversible transition, the Gibbs energy barrier to the reversible transition, and preferably also the previously described preferences thereof and associations/involvements therewith (collectively referred to hereafter as the state transition characteristics).

The two-state capability and the state transition characteristics endow the molecule or molecular specie with useful or desirable properties, as discussed later.

The two-state capability and the state transition characteristics can be influenced by steric effects associated with selected substituents or moieties or sub- structures of (or on) the macrocycle (referred to hereafter as the macrocycle adjuncts). In particular, the macrocycle adjuncts are preferably portions of the molecule or molecular specie that are in addition to the invertible dipole, the atoms forming the cyclically ordered (sub)set(s) of bonds, and the parent structure of the macrocycle.

It is desirable that the macrocycle adjuncts (if any) are selected so as to avoid steric hindrance that would undesirably interfere with the two-state capability and/or the state transition characteristics, e.g. by the macrocycle adjuncts sterically hindering or destabilising either one (or both) of the two configurations of the invertible dipole.

Said differently, the macrocycle adjuncts (if any) are preferably selected such that each of the first and second sides of the macrocycle (or of the molecule or molecular specie) can sterically accommodate (or sterically allow) each of the two

configurations of the invertible dipole, and preferably also sterically accommodate (or sterically allow) any distortions in the macrocycle that are desirable (however, macrocycle rigidity or substantial macrocycle rigidity is preferred in most

circumstances for the state transition characteristics, as discussed previously).

Preferably, the macrocycle adjuncts are configured to (advantageously) isolate the invertible dipole from intra-molecular steric interactions. Specifically it will be appreciated that this is a steric isolation/accommodation. Some instances of the invention do require a significant dipole-dipole intra- and inter-molecular interactions.

Preferably, the macrocycle adjuncts are selected to provide a space or volume or central cavity that is devoid or substantially devoid of steric influence or electron orbitals or electron cloud (hereafter called the sterically vacant space), on at least one and more preferably each of the first and second sides of the macrocycle, that can sterically accommodate (or sterically allow) each of the two configurations of the invertible dipole. More preferably, each of the two sterically vacant spaces is centred or substantially centred on the macrocycle axis.

Preferably, each of the two sterically vacant spaces is surrounded (or substantially surrounded) by the macrocycle adjuncts for sterically protecting the invertible dipole and/or X _f , X _g , X _h, and Xi from inter-molecular interactions. Preferably, the steric protection can (advantageously) isolate the invertible dipole from inter-molecular steric interactions, including when in a solid or crystalline or tethered (or otherwise rotationally-constrained) state.

Preferably, the steric protection is provided (or substantially provided) by the macrocycle adjuncts for directional components of inter-molecular interactions that are parallel or substantially parallel to the macrocycle axis. Also preferably, the steric protection is provided (or substantially provided) by the macrocycle adjuncts for directional components of inter-molecular interactions that are parallel or substantially parallel or oblique to the plane of the macrocycle (or the plane of X _f , X _g , X _h , and Xi).

Preferably, at least one of, and more preferably each of, the two sterically vacant spaces is open (or substantially open) in a direction extending along or parallel to the macrocycle axis and away from a corresponding one of the first and second sides. More preferably, the macrocycle adjuncts are relatively compact. These preferences (advantageously) minimise steric shielding of the invertible dipole (and in particular where one or both of the first and second dipole states has an overall net electric dipole m that is parallel or substantially parallel to the macrocycle axis). It will be appreciated that the steric shielding is just that; steric and that the orientation of the dipole is an independent aspect. Whether the dipole be a- or c-axis oriented as shown in Fig. 4 still requires exactly the same kind of steric accommodation. The dipole orientation is dependent upon the electronegativity and orbital involvement of all 5 atoms of the bridge. The dipole orientation of the B(F)OB(F) moiety is about 80 degrees different to that of B(F)SB(F) even though they have very similar steric requirements. Preferably, the macrocycle adjuncts are selected to provide one, more preferably two, most preferably three, and ideally more than three local maxima in steric height(s) as measured from the plane of X _f , X _g , X _h , and Xi away from the first side, that is (or are) substantially equal to or more preferably greater than a maximum steric height of the invertible dipole as measured from the plane of X _f , X _g , X _h , and Xi away from the first side (whether occurring in the first or the second isomer or conformer).

Preferably, the local maxima in steric height(s) above the first side correspond to positions that are co-planar or substantially co-planar. Preferably, the local maxima in steric height(s) above the first side correspond to positions that are evenly distributed or substantially evenly distributed about the macrocycle.

Preferably, the macrocycle adjuncts are also selected to provide one, more preferably two, most preferably three, and ideally more than three local maxima in steric height(s) as measured from the plane of X _f , X _g , X , and X _f away from the second side, that is(are) substantially equal to or more preferably greater than a maximum steric height of the invertible dipole as measured from the plane of X _f , X _g , X _h , and Xi away from the second side (whether occurring in the first or the second isomer or conformer).

Preferably, the local maxima in steric height(s) above the second side correspond to positions that are co-planar or substantially co-planar. Preferably, the local maxima in steric height(s) above the second side correspond to positions that are substantially evenly distributed about the macrocycle.

Said differently, the macrocycle adjuncts preferably provide a steric extent as measured along the macrocycle axis (e.g. between a globally maximum one of the local maxima in steric height(s) from the first side, and a globally maximum one of the local maxima in steric height(s) from the second side) that can sterically accommodate (or sterically allow) each of the two configurations of the invertible dipole, and that can sterically protect the invertible dipole from inter-molecular interactions. Preferably, the macrocycle adjuncts are selected to be substantially sterically contiguous about at least one of, and more preferably about each of, the two sterically vacant spaces.

‘Substantial steric contiguity’ as used herein refers to a configuration of the macrocycle adjuncts wherein, in each plane parallel to the plane of X _f , X _g , X _h , and Xi, that transects a given one of the sterically vacant space(s), and that resides within the steric extent of the macrocycle adjuncts from the first and second sides, the steric influence (or electron orbitals or electron density distribution or electron cloud) of the macrocycle adjuncts about the given one of the two sterically vacant spaces is contiguous or substantially contiguous but for gaps or sterically vacant portions (if any) in each said plane of less than 10A, more preferably less than 5A, and most preferably less than 2A.

Preferably, the macrocycle adjuncts (if any) are kinetically stable, or exhibit low or substantially low (or more preferably zero or substantially zero) net molecular displacement relative to the macrocycle or the plane of the macrocycle or the plane of X _f , X _g , X _h , and Xi.

Preferably, the macrocycle adjuncts are substantially rigid and/or shape-invariant toward the invertible dipole, or between different states or configurations of the invertible dipole (or between all isomers or conformers of the molecule or molecular specie, in particular the first and second isomers or conformers).

Preferably, the macrocycle adjuncts are of low polarity or substantially low polarity. Preferably, the macrocycle adjuncts are only comprised of carbon and hydrogen or other chemical elements of similar electronegativity to carbon or hydrogen, but for any structures to promote tethering or crystallisation (as introduced later). More preferably, the macrocycle adjuncts are only comprised of carbon and hydrogen.

Advantageously, low polarity of the macrocycle adjuncts (and also of the macrocycle) tends to: minimise electrical conductivity (for most applications), minimise the directionality of inter-molecular interactional forces or contact forces (for promoting ordering of the molecules or molecular species in a material). However, the polarity of the macrocycle adjuncts (and/or of the macrocycle), and hence the electrical conductivity, can be varied through the selection of constituent atoms from that of an insulator to that of a semi-conductor (for some applications).

Advantageously, the preferred extensive conjugation in the macrocycle, and also as preferred between the cyclically-ordered (sub)set(s) of bonds and the atoms or structures X _f , X _g , X _h, and Xi, promotes an overall macrocyclic planarity that provides a stable backbone or stable scaffold for the macrocycle adjuncts to provide the previously described steric allowance and steric protection.

The preferred form of the macrocycle adjuncts (in particular, a number of the above described preferences) said differently: there is preferably provided a (molecular) box or boundary for the invertible dipole.

A number of the above described characteristics are summarised below.

Preferably, the box is comprised of substituents or moieties of (or bonded onto) the macrocycle. Preferably, the box is formed from wall(s) or posts(s) that surround(s) the invertible dipole or that is/are disposed about the perimeter of the invertible dipole. Preferably, the substituents or moieties that form the box, or the walls or posts of the box, are sterically demanding. Preferably, the box encircles or surrounds or (or contains) the invertible dipole, or spatially isolates the invertible dipole from inter- molecular steric interactions. Preferably, the box spatially extends an otherwise planar macrocycle in a direction of the macrocycle axis, at least as far as the extents of the invertible dipole along the same macrocycle axis. Preferably, the box walls are symmetrical above and below the plane of the macrocycle. Preferably, the box is open on each of the first and second sides of the macrocycle. Preferably, the box sterically protects the invertible dipole from inter-molecular steric interactions (or to a substantial degree), without shielding the invertible dipole from forming an electric field that extends beyond the box (or relatedly, without shielding the invertible dipole from being influenced by the externally applied electric field). Said differently, the box is preferably compact whilst also providing the steric protection. Preferably, the box is temporally well-defined. Preferably, the box sterically allows the inversion pathways. The molecule or molecular specie that includes the invertible dipole and the macrocycle, when provided with the box, is referred to hereafter as the‘invertible- dipole-in-a-box’ (as a convenient reference to the characteristics of the macrocycle adjuncts discussed in this section).

The invertible-dipole-in-a-box rationale can advantageously provide full predictability (and relatedly, scalability) of properties of a material composed therefrom and devices made therewith, from a molecular scale to a bulk meso-scale or macroscopic scale, and vice versa, and also advantageously, the mechanism does not rely upon defects being formed in the active medium (as for doped silicon and ferroelectric polymers).

Preferably at least one, more preferably at least two, and most preferably three or four, of the macrocycle adjuncts (each) include(s) at least one (but more preferably only one) cyclic structure(s) (or similar group having a capability for steric or spatial rigidity in a direction parallel to the macrocycle axis, and more preferably also in a direction perpendicular to the macrocycle axis).

Preferably at least one, more preferably at least two, and most preferably three or four, of the cyclic structure(s) of the macrocycle adjuncts (each) include(s) at least one (but more preferably only one) aromatic ring(s).

Preferably at least one, more preferably at least two, and most preferably three or four, of the aromatic ring(s) of the macrocycle adjuncts is/are (each) aryl moiety(s).

Preferably at least one, more preferably at least two, and most preferably three or four, of the aryl moiety(s) of the macrocycle adjuncts (each) contain(s) a six-carbon ring or comprise(s) a phenyl group.

Preferably at least one, more preferably at least two, and most preferably three or four, of the aromatic ring(s) or aryl moiety(s) of the macrocycle adjuncts (each) has at least one, more preferably at least two, and most preferably four, substitution(s) (or structure(s) bonded to the corresponding cyclic portions) of the aromatic ring(s) or aryl moiety(s). Preferably at least one, more preferably at least two, and most preferably four of the substitution(s) (or structure(s) bonded to the corresponding cyclic portions) of the aromatic ring(s) or aryl moiety(s) of the macrocycle adjuncts, is/are (each) alkyl moiety(s).

Preferably at least one, more preferably at least two, and most preferably four of the alkyl moiety(s) of the macrocycle adjuncts is/are (each) methyl groups.

Preferably at least one, and more preferably two, of the substitution(s) (or structure(s) bonded to the corresponding cyclic portions) of the aromatic ring(s) or aryl moiety(s) of the macrocycle adjuncts, is/are bonded to a first atom that is bonded to a second atom, wherein the second atom is bonded to the macrocycle.

Preferably, at least two of the substitution(s) (or structure(s) bonded to the

corresponding cyclic portions) of the aromatic ring(s) or aryl moiety(s) of the macrocycle adjuncts, have a meta-positional relationship relative to one another.

Preferably at least one, more preferably at least two, and most preferably three or four, of the macrocycle adjuncts (each) has/have a meso symmetry (being a stereoisomer with an identical or superimposable mirror image). More preferably, the meso symmetry has an internal mirror plane that passes (or substantially passes) through the atom of the corresponding one of the macrocycle adjuncts that is bonded to the macrocycle (e.g. the second atom of the aromatic ring(s) or aryl moiety(s)).

Said differently, preferably at least one, more preferably at least two, and most preferably three or four (or more), of the macrocycle adjuncts (each) has/have at least one (and more preferably two) substituent(s) in an ortho position for sterically interacting with at least one (and more preferably two) of the atom(s) of the macrocycle (or the nearest atom(s) of the macrocycle when the corresponding one of the macrocycle adjuncts is rotated about an ipso bond thereto). More preferably, there are provided two or/ho-positioned substituents that are disposed opposite from one another on the first and second sides of the macrocycle, respectively. These characteristics can advantageously orient (or spatially constrain) the macrocycle adjuncts for providing the desired box or steric protection.

Preferably, the or/ho-positioncd substituent(s) are selected from the class consisting of alkyl (more preferably methyl, ethyl, or iso-propyl), CF ₃ , and Cl.

Preferably at least one, more preferably at least two, and most preferably three or four (or more), of the macrocycle adjuncts (each) has/have at least one (and more preferably two) substituent(s) in a meta position. More preferably, there are provided two me/a-positioned substituents that are disposed opposite from one another on the first and second sides of the macrocycle, respectively. The me/a-positioned substituent(s) preferably provide (or further increase) Van der Waals or other inter- molecular interactions that tend to rotationally constrain the molecule or molecular specie.

Preferably, the me/a-positioned substituent(s) are selected from the class consisting of alkyl (more preferably methyl, ethyl, or iso-propyl), CF ₃ , and Cl.

Preferably at least one, more preferably at least two, and most preferably three or four (or more), of the macrocycle adjuncts (each) has/have at least one substituent(s) in a para position. The para-positioned substituent(s) preferably provide (or further increase) Van der Waals or other inter- molecular interactions that tend to rotationally constrain the molecule or molecular specie. However, it will be understood the ortho substituents are most important.

Preferably, the para-positioned substituent(s) are selected from the class consisting of alkyl (more preferably methyl, ethyl, iso-propyl, or tert-butyl), aryl, CF ₃ , and Cl.

Depending upon the selection of constituent atoms or structures, the substituents(s) of the macrocycle adjuncts can have the structure(s)/configuration(s) represented in Figure 5 is a representation of preferred structure(s)/configuration(s) for the macrocycle adjunct(s) of the invertible-dipole-in-a-box, more preferably when the macrocycle adjunct(s) comprises an aryl or phenyl group as illustrated. The structure(s) and/or configuration(s) are represented as a stick model. The ortho- positioned substituent(s) are represented as A, A’, the meta-positioned substituent(s) are represented as B,B’, and the para-positioned substituent(s) are represented as C,C\ The macrocycle (or the atom of the macrocycle that is bonded to the macrocycle adjunct(s)) is represented as‘me’.

Preferably at least one, more preferably at least two, and most preferably three or four, of the cyclic structure(s) or aromatic ring(s) or aryl moiety(s) of the macrocycle are oriented orthogonal (or substantially orthogonal) to the plane of the macrocycle (or the plane of X _f , X _g , X _h , and Xi). For example, l,6-dimethylphenyl meso substituents on a porphyrin have (or tend to have) an orientation that is substantially orthogonal to the plane of the porphyrin.

Depending upon the selection of constituent atoms or structures of the molecule or molecular specie according to preferred embodiments, the box can have the structure/configuration represented in Figure 6

Fig. 6 is a representation of the box in the invertible-dipole-in-a-box when the molecule or molecular specie is provided as a B ₂ OF ₂ -me,sO-tetradurylporphyrin. In Fig. 6A the molecule or molecular specie according to preferred embodiments is represented as stick models. In Fig 6B the macrocycle and the invertible dipole are represented as stick models, and the macrocycle adjuncts and an underlay of the invertible dipole are represented as space-filling models. The nearest one of the macrocycle adjuncts is represented as a stick model. The steric extent of the macrocycle adjuncts, and also of the invertible dipole, are represented by dotted lines that are black (for the macrocycle) and red (for the invertible dipole).

As illustrated in each of Figs 6A & 6B the methyl groups on each of the meso- aryl substituents (a preferred selection of the macrocycle adjuncts) advantageously force (or result in) the corresponding aromatic rings to be substantially disposed orthogonal to the plane of the macrocycle (or the plane of X _f , X _g , X _h , and X _f ). This configuration of the aromatic rings, and the steric extent of the meso- aryl substituents, provides sufficient space to sterically accommodate the central B ₂ OF ₂ group (a preferred selection of the invertible dipole), in particular the more sterically demanding ample portion of the invertible dipole that has a greater spatial extent away from the macrocycle (as illustrated). This configuration can also form the two sterically vacant spaces, and can provide the steric protection from inter-molecular interactions.

Depending upon the selection of constituent atoms or structures, the box can have the structure(s) represented in Figure 7. As illustrated therein, the macrocycle (preferably a porphyrin or porphyinoid) is preferably provided with at least four, and more preferably six or eight, of the macrocycle adjuncts. In Fig. 7C there is shown a diaza- bacteriochlorin and is an example of where there are just two aryls with peripheral methyl groups directly on the macrocycle that contribute (though less so than the aryls) to the steric shielding for an invertible dipole group.

In Fig. 7 there is shown a representation of preferred structure(s) of the box for the invertible dipole-in-a-box, more preferably when the molecule or molecular specie is a porphyrin or porphyinoid, having Fig. 7 A four of the macrocycle constituents (preferred as methyl-substituted aryl rings), and having Fig. 7B six of the macrocycle constituents (preferred as methyl-substituted aryl rings). The structure(s) of the box are represented as stick models. Also illustrated are the preferred porphyrin or porphyinoid parent structures (as stick models adjoined thereto with some non-carbon atoms and parent hydrides indicated).

Packing effects

The molecule or molecular specie (or the invertible-dipole-in-a-box) is preferably provided with a means for improving or increasing (or at least providing) a spatial ordering or packing of more than one of the molecule(s) or molecular specie(s) when provided together (whether of the same type or more than one type, but conveniently described hereafter with reference to a singular type of the molecule or molecular specie; hereafter called the means for packing the molecule(s) or molecular species(s)).

Preferably, the spatial ordering or packing is so improved, or increased, or at least provided, in (or substantially in) the plane of the macrocycle or the plane of X _f , X _g , X _h , and Xi. Preferably, the molecule or molecular specie (or the invertible-dipole-in-a-box, or the macrocycle when provided with the macrocycle adjuncts) has a rotational symmetry.

Also preferably, the rotational symmetry contributes to, or is associated with, or constitutes, the means for packing the molecule(s) or molecular species(s).

Preferably, the molecule or molecular specie (or the invertible-dipole-in-a-box, or the macrocycle when provided with the macrocycle adjuncts) has C2 symmetry or higher, higher meaning exhibiting a greater number of symmetry elements and preferably C ₂ , or pseudo-C ₂ , or substantial C ₂ , order of the rotational symmetry, and most preferably has a C ₄ , or pseudo-C ₄ , or substantial C ₄ , order of the rotational symmetry. This includes D _N .

Also preferably, the rotational symmetry is provided about an axis that is orthogonal or substantially orthogonal to the plane of the macrocycle or the plane of X _f , X _g , X _h, and Xi, and more preferably parallel or substantially parallel to the macrocycle axis. This can (advantageously) orient (or be used to orient) the spatial ordering or packing (or one component thereof) in (or substantially in) the plane of the macrocycle or the plane of X _f , X _g , X _h , and Xi (in particular, for providing e.g. the preferred layer or monolayer, as later introduced). It is understood that symmetries relating to reflection planes and inversion centres will contribute to the packing of the molecule(s) or molecular specie(s) according to preferred embodiments.

The above preferred relationships of the rotational symmetry can be seen e.g. in Figs 6 and 7. However, the suitability of a given order of the rotational symmetry for a given one of the molecule or molecular specie (or of the invertible-dipole-in-a-box, or of the macrocycle when provided with the macrocycle adjuncts), can depend upon the order (k ^h ) of the polydentate or multidentate ligand structure of that given one of the molecule or molecular specie.

Therefore said differently, the molecule or molecular specie (or the invertible-dipole- in-a-box, or the macrocycle when provided with the macrocycle adjuncts), preferably has an order of the rotational symmetry that is a proper divisor of, or equals, or is a multiple of, the order of the polydentate or multidentate ligand structure. When (advantageously) used for improving, or increasing, or at least providing, the spatial ordering or packing, the (preferred) rotational symmetry can relate to, or be associated with, a number of inter-molecular interaction(s) and/or bond(s) formed between the more than one of the molecule(s) or molecular specie(s) (hereafter called the inter-molecular packing interaction(s) and/or bond(s)).

Said differently, there can (preferably) be provided (or additionally provided) a symmetry(s) (or a substantial or pseudo one(s) thereof) in the existence (or a potential therefor) and/or in the energetic magnitude (or a potential therefor) and/or in the directionality (or a potential therefor) of the inter-molecular packing interaction(s) or bond(s) (hereafter conveniently called the interactional symmetry(s)).

The possible forms of symmetry(s) of the interactional symmetry(s) can be broader or more numerous than for the rotational symmetry(s) (but can nonetheless include a rotational form of symmetry), and in particular when the inter-molecular packing interaction(s) and/or bond(s) include polar or directional or otherwise asymmetric interaction(s) and/or bond(s) (or a potential(s) therefor), or when there is provided more than one type of the molecule or molecular specie (e.g. for forming a repeated pattern in the spatial ordering or packing), provided that the interactional symmetry(s) are selected to be suitable for the improving, or the increasing, or the providing, of the spatial ordering or packing (e.g. an overall energetic favourability is provided for the spatial ordering or packing, having regard e.g. to opposite electrostatic charges attracting, and/or differences or asymmetry(s) in atoms or electron orbitals being required for certain interaction(s) and/or bond(s), etc.)

In a simple form of the interactional symmetry(s), the previously described (preferred) order(s) and orientation(s) of the rotational symmetry can correspondingly apply (or otherwise, be applied) to the interactional symmetry(s), but especially when the inter- molecular packing interaction(s) or bond(s) (or a potential(s) therefor) are non-polar and non-directional and symmetric (or substantially so), e.g. a configuration of Van der Waals interactions. It is generally preferred to minimise the directionality and/or the polarity and/or other asymmetry(s) in the inter-molecular packing interaction(s) and/or bond(s), for promoting the spatial ordering or packing (and/or for minimising a polarity of the macrocycle or macrocycle adjuncts, and/or for minimising shielding of the invertible dipole, and/or for minimising a or a contribution of the macrocycle or macrocycle adjuncts to the overall net electric dipole m).

Preferably, the molecule or molecular specie (or the invertible-dipole-in-a-box, or the macrocycle when provided with the macrocycle adjuncts) can form one or more inter- molecular aromatic-aromatic interaction(s) or pi-electron interaction(s) (e.g. pi-bond stacking) between the more than one of the molecule(s) or molecular specie(s) (hereafter called the inter- molecular pi-electron interaction(s)).

Preferably, the inter-molecular pi-electron interaction(s) include(s) or involve(s) (whether wholly or in part, but preferably wholly or substantially) at least one (more preferably at least two, and most preferably three or four) sandwich configured or parallel-displacement configured ones of the (preferred) aromatic ring(s) of the macrocycle adjuncts for a given one of the molecule or molecular specie. It will be appreciated by a skilled addressee that is not an exhaustive/complete listing of intermolecular dispersion forces and can be generalised by reference to

“intermolecular dispersion forces and/or induced-dipole-induced-dipole interactions”.

Energetics in state transition

As previously described, the later disclosed applications (in particular electrical or electronic applications) depend upon the externally applied electric field (as applied to the molecule or molecular specie at a molecular level) being capable of triggering or mediating or causing the inversion(s) between the two configurations of the invertible dipole.

Said differently, at least one of (and most preferably both of) the first and second directions of the externally applied electric field (e.g. as pre-determined for a given application) can energetically favour a corresponding one of the first and/or second transitions. In particular, when the externally applied electric field is oriented in the first direction, the Gibbs energy (or Gibbs free energy) of the second isomer or conformer (or ground state) relative to that of the first isomer or conformer is reduced (and that of the latter relatively increased); and/or when the externally applied electric field is oriented in the second direction, the Gibbs energy of the first isomer or conformer (or ground state) relative to that of the second isomer or conformer is reduced (and that of the latter relatively increased). Similarly, it is noted that Gibbs energy barrier is sometimes termed‘energy barrier’ and refers to the activation energy for a process, that being the energy of the transition state for that process relative to the starting state (the‘ground state’).

Preferably, the absolute Gibbs energy(s) of at least one of (and more preferably both of) the first and second isomers or conformers is/are reduced when the externally applied electric field is oriented in a corresponding one(s) of the second and first directions respectively, and further preferably is/are also increased when the externally applied electric field is oriented in a reciprocal one(s) of the second and first directions, respectively.

Associated with the above characteristics, at least one of the Gibbs energy barrier(s) to the reversible transition (whether of the first and/or second transition, but preferably both) can (advantageously) be lowered in magnitude by the presence of the externally applied electric field (when applied in a corresponding one(s) of the first and second directions, respectively); and can preferably be increased in magnitude by the presence of the externally applied electric field (when applied in a reciprocal one(s) of the first and second directions).

For most applications, all of the foregoing characteristics are required or substantially required, in the molecule or molecular specie (relatedly, likewise for perfect reversibility in the reversible transition, and zero or substantially zero degradation in an operational environment). These can be application-specific considerations, and non-ideal behaviours (associated e.g. with degradation) are not necessarily problematic for some applications, in particular where only one or a substantially small number (e.g. <10) of manipulations and/or interrogations are required (e.g. disposable temperature probes). The foregoing characteristics are conveniently referred to hereafter as the electrically- mediated bias of the state transition characteristics.

In accordance with the electrically-mediated bias, a pre-determined magnitude (in a pre-determined direction) of the externally applied electric field can thermally destabilise a pre-determined one of the first and second isomers or conformers (or ground states), or said differently reduce or nullify or override the thermal stability against a pre-determined one of the inversion(s) or associated inversion pathways(s).

For the reduction in the thermal stability, wherein a pre-determined one of the Gibbs energy barrier(s) to the reversible transition (in particular, to the pre-determined one of the first and second transitions that involves the pre-determined inversion) is reduced but remains positive in magnitude, the reversible transition (in particular, the pre-determined transition) can be thermally activated. The kinetics of the thermal activation can be pre-determined by the magnitude and direction of the externally applied electric field (and/or by a temperature of operation as pre-determined for a given application). Preferably, the kinetics of the thermal activation are of the first order.

For the nullification in the thermal stability, wherein the pre-determined one of the Gibbs energy barrier(s) to the reversible transition is reduced to zero (or near zero or substantially zero) in magnitude, the reversible transition (in particular, the pre determined transition) can be spontaneous or substantially spontaneous.

For the overriding in the thermal stability, wherein the externally applied electric field exceeds the component magnitude where at the pre-determined one of the Gibbs energy barrier(s) to the reversible transition ceases to exist, the reversible transition (in particular, the pre-determined transition) can also be spontaneous.

The converse capability(s) of the electrically-mediated bias can preferably also apply.

In particular, another pre-determined magnitude and/or another pre-determined direction of the externally applied electric field can thermally stabilise the (or another) pre-determined one of the first and second isomers or conformers (or ground states), or said differently increase the thermal stability against the (or another) pre determined one of the inversion(s) or associated inversion pathways(s), or said differently the (or another) pre-determined one of the Gibbs energy barrier(s) to the reversible transition is increased in magnitude.

These capabilities of the electrically-mediated bias relate to the orientation of the overall net electric dipole m of the molecule within the externally applied electric field.

In other words, the lowering in magnitude(s) or the increasing in magnitude(s) of the Gibbs energy barrier(s) to the reversible transition (and relatedly, the changes in relative and/or absolute Gibbs energy(s) of the first and/or second isomers or conformers) due to the presence of the externally applied electric field (when applied in pre-determined direction(s)) in any given instant, depends upon whether the externally applied electric field (or vector thereof) exhibits a parallelism or co directionality (whether in part or wholly), or an anti -parallelism or anti-directionality (whether in part or wholly), to the molecular dipole moment (or the vector component of the overall net electric dipole m) of the molecule or molecular specie (whether existing as the first or isomer or conformer) in that given instant.

In particular, the parallelism or co-directionality will tend to trigger or mediate or cause the inversion(s) between the two configurations of the invertible dipole (said differently, like charges repel). Conversely, the anti-parallelism or anti-directionality will tend to restrain or inhibit or prevent the inversion(s) (said differently, opposite charges attract).

Said differently, if the externally applied electric field (or vector E thereof) opposes (whether wholly or in part), or is aligned with (whether wholly or in part), the molecular dipole moment (or the vector component of the overall net electric dipole m and any induced electric dipole), a Gibbs energy barrier (AG ^: ) to a (or any) change in state (between the first and second isomers or conformers, whether involving the first transition or the second transition) is increased in magnitude, or is decreased in magnitude, respectively. This relates to the following equation for the total energy U _L1 under the externally applied electric field E, and relates the invertible dipole (advantageously) being a significant contributor to the overall molecular electric dipole (m): u _m = -m · E

It is to be noted that that the electric field definition requires consistency with that defining the electric dipole of the molecule.

However, the effect (whether isomerisation or conformerisation, or another process) of the externally applied electric field upon any given one of the molecule or molecular specie depends upon the degree (if any) of spatial constraint imposed upon the given molecule or molecular specie.

A free (or spatially unconstrained) one of the molecule or molecular specie will have a rotational molecular vibration (in particular, at commercially useful temperatures), or otherwise have a relatively low Gibbs energy barrier(s) to a rotated configuration (that can be readily activated e.g. via the transfer of energy during inter-molecular interactions), whereby each of the inversion pathways(s) between the two

configurations is substantially less energetically favourable, than a simple thermal rotation of the molecule or molecular specie that re-aligns the molecular dipole moment (or the vector component of the overall net electric dipole m) to be anti parallel or anti-directional (whether in part or wholly) to the externally applied electric field (or vector E thereof). Relatedly, the free molecule or molecular specie can (thermally) lose an alignment to the externally applied electric field, in the absence of that field.

The foregoing can be true even if the externally applied electric field at full strength could otherwise substantially nullify or override a given one of the Gibbs energy barrier(s) to the reversible transition, due to the timeframe(s) (or slew rates) required for modem electrical or electronic devices to form the externally applied electric field. Accordingly, for most applications the molecule or molecular specie (or at least one of the first or second isomers or conformers thereof, but most preferably both) is (advantageously) spatially constrained, and in particular rotationally constrained, and especially for electrical or electronic devices that rely upon a pre-determined persistence or permanence in a spatial correlation between one or more state(s) of the molecule(s) or molecular specie(s) constituting the device, and the means of forming the externally applied electric field (for e.g. a read-write head or tip of a memory element).

Spatial constraints

There can be provided a singular one of the molecule or molecular specie according to preferred embodiments. There can also be provided (as preferred for most

applications) a population of the molecule(s) or molecular specie(s).

The population can be comprised of a plurality of (one or more types of, but preferably only one type of) the singular ones, and therefore the following description regarding the singular ones can also apply severally to one or more of the singular ones that constitute the population.

For most applications (especially for electrical or electronic devices as discussed previously), the singular one or population (in particular, at least one of the first or second isomer(s) or conformer(s) thereof, but most preferably both and especially for electrical or electronic devices) is advantageously constrained or localised, or substantially constrained or localised, to a pre-determined spatial confine (e.g. a read- write domain) for at least a pre-determined period of time (e.g. a read-write cycle, or an expected device lifetime).

It is also advantageous for most applications (especially for electrical or electronic devices as discussed previously) to rotationally constrain, or substantially rotationally constrain, each (or substantially each, or a substantial number) of the singular one or population (in particular, at least one of the first or second isomer(s) or conformer(s) thereof, but most preferably both and especially for electrical or electronic devices) for at least the pre-determined period of time. The pre-determined spatial confine and/or period of time can be application specific, as they correspondingly define the space within, and/or time during which, the two- state capability and/or the state transition characteristics and/or the electrically mediated bias, and the molecule(s) or molecular specie(s) generally, are manipulated, interrogated, energised, de-energised, or otherwise exploited (e.g. by an electrical or electronic device), and/or are exposed or subjected to, and/or interacted with, and/or triggered to cause or mediate, a thermal and/or electric and/or magnetic effect or environment (whether static or time-varying). These aspects are conveniently referred to hereafter as the functions of the molecule or molecular specie.

The constraint or localisation to the pre-determined spatial confine can be performed using a number of means known in the art, but preferably using (or involving) the means as described below. Also preferably, the rotational constraint is preferably performed using (or involving) the means as described below.

In general terms, there is preferably provided a means for constraining or localising, or substantially constraining or localising, the singular one or population (or at least one of the first or second isomer(s) or conformer(s) thereof, but most preferably both), against translation (hereafter called the means for translational constraint) along each one (or any combination of ones) of three pre-determined orthogonal axes (hereafter called the axes of translational constraint) out of the pre-determined spatial confine over the pre-determined period of time.

There is also preferably provided a means for constraining, or substantially

constraining, each (or substantially each, or a substantial number) of the singular one or population (or at least one of the first or second isomer(s) or conformer(s) thereof, but most preferably both), against rotation (hereafter called the means for rotational constraint) about at least one corresponding pre-determined axis, more preferably about two corresponding pre-determined orthogonal axes, and most preferably about three corresponding pre-determined orthogonal axes of rotation of each corresponding one of the single one or population (hereafter collectively called the axes of rotational constraint). Preferably, the means for translational and/or rotational constraint(s) include(s) a substrate that is comprised of a plurality of atoms. Preferably, the substrate takes the form of a surface (e.g. providing a steric limit in one direction) or a layer (more generally; e.g a sandwich of successive contiguous stratifications providing the steric limit in the one direction, but there also potentially being provided another steric limit in a reciprocal direction such as by another layer, e.g. as in a layer-cake; but also potentially describing a layer that has a surface).

Preferably, the means for translational and/or rotational constraint(s) include(s) or involve(s) a number of inter-molecular interaction(s) and/or bond(s) (preferably other than steric effects) between each (or substantially each, or a substantial number) of the singular one or population and the substrate (conveniently referred to hereafter as the tethering interaction(s) and/or bond(s); but potentially involving physisorption and/or chemisorption, either severally or concurrently), that provide corresponding Gibbs energy(s) against translation(s) and/or Gibbs energy(s) against rotation(s), and that collectively provide a total Gibbs energy of association/disassociation of the tethering interaction(s) or bond(s) for constraining each corresponding one(s) of the singular ones or population to the substrate.

Relatedly, there is preferably provided a process of depositing each (or substantially each, or a substantial number) of the singular one or population onto the substrate for constraining (or tethering) each (or substantially each, or a substantial number) of the corresponding one(s) of the singular ones or population to the substrate, whereby the tethering interaction(s) and/or bond(s) are formed (hereafter called the deposition). The deposition can have one or more pre-determined temperature(s).

The population (when the molecule(s) or molecular specie(s) is/are provided as such) is also preferably provided (whether wholly or in part) with the spatial ordering or packing, as previously described. Relatedly, the means for translational and/or rotational constraint(s) preferably include(s) or involve(s) the inter-molecular packing interaction(s) and/or bond(s), as previously described.

The population (when provided with the inter-molecular packing interaction(s) and/or bond(s)) can (preferably) be provided as one contiguously (or substantially or partly contiguously) ordered or packed (or interacted and/or inter-bonded) population, or otherwise as two or more contiguously (or substantially or partly contiguously) ordered or packed (or interacted and/or inter-bonded) sub-populations. The spatial ordering or packing can also be described as having a corresponding degree of the spatial ordering or packing (or a corresponding degree of the inter-molecular packing interactions and/or bonds), for each corresponding one of the population and/or the sub-populations thereof (collectively referred to hereafter as the degree(s) of ordering or packing).

A total Gibbs energy of association/disassociation of the inter-molecular packing interaction(s) and/or bond(s) in the population, or across all of the sub-populations, provides a convenient relative measure of (or reference to, or definition of) the number of the sub-populations (if any) and/or an average of the degree(s) of ordering or packing (referred to hereafter as the total Gibbs energy of the packing interaction(s) and/or bond(s)).

Relatedly, there is preferably provided a process of annealing the population for improving or increasing the degree(s) of ordering or packing (or for improving or increasing the total Gibbs energy of the packing interaction(s) and/or bond(s);

hereafter called the annealing). The annealing can have one or more pre-determined temperature(s).

The annealing said differently, a gradual (or substantially gradual) reduction in the pre-determined annealing temperature(s), or otherwise a selection(s) of the pre determined annealing temperature(s) that is/are suitably lower than the pre-determined depositional temperature(s), or otherwise a selection(s) of the pre-determined depositional temperatures(s) that is/are suitably low, can provide (or improve or increase) the degree(s) of ordering or packing (or the total Gibbs energy of association/disassociation of the packing interaction(s) and/or bond(s)), when compared with the absence of a performing of the annealing.

Preferably, the annealing is performed (whether wholly or in part) during (or at least partly during) the deposition, however the annealing can also be performed as a process that is separate from (or substantially separate from), and subsequent to (or substantially subsequent to), the deposition.

Whether the molecule(s) or molecular specie(s) is/are provided as the singular one or as the population, the following preferences can apply.

The total Gibbs energy of the tethering interaction(s) of each tether and/or bond(s) is preferably chemisorption-related, and also preferably exceeds 40 kJ mol ¹ , more preferably exceeds 70 kJ mol ¹ , and most preferably exceeds 100 kJ mol ¹ .

Combinations of the above preferences can yield preferred ranges of the total Gibbs energy of the tethering interaction(s) and/or bond(s) of preferably 40 to 300 kJ mol ¹ , more preferably 70 to 250 kJ mol ¹ , and most preferably 100 to 150 kJ mol ¹ .

The above described preferences of the total Gibbs energy of the tethering

interaction(s) and/or bond(s) can (advantageously) provide the means for translational and/or rotational constraint(s) whilst also (relatedly) permitting the spatial ordering or packing (when the molecule(s) or molecular specie(s) is/are provided as a population).

Furthermore, the above described preferences of the total Gibbs energy of the tethering interaction(s) and/or bond(s), are amenable (or can be made amenable) to the annealing, and advantageously for selection(s) of the pre-determined annealing temperature(s) that are within practical limits.

When the molecule(s) or molecular specie(s) is/are provided as the population, the following preferences can apply.

Combinations of the above preferences can yield a preferred ratio of the total Gibbs energy of the tethering interaction(s) and/or bond(s), to the total Gibbs energy of the packing interaction/ s) and/or bond(s), of preferably at most 15:1, more preferably at most 10:1, and most preferably at most 5:1 or 3:1, but also preferably at least 1-5:1, and more preferably at least 2-5:1. These preferred ratios can (advantageously) permit the spatial ordering or packing, and are amenable (or can be made amenable) to the annealing.

However, one(s) of the total Gibbs energy of the tethering interaction(s) and/or bond(s) that are substantially higher than corresponding ones of the total Gibbs energy of the packing interaction(s) and/or bond(s), can be associated with a reduction in the degree(s) of ordering or packing, or even a substantial absence of the spatial ordering or packing (and can relatedly render the annealing more difficult).

A number of means for correspondingly increasing the total Gibbs energy of the packing interaction(s) and/or bond(s) can be disadvantageous, e.g. some means that involve an increase in a diameter or maximum diameter of the macrocycle and/or of the macrocycle adjuncts, and/or an increase in a polarity of the macrocycle and/or the macrocycle adjuncts, and/or an increase in asymmetry(s) or directionality(s) or polarity(s) in the inter-molecular packing interaction(s) and/or bond(s).

Accordingly, the above described preferences represent one form of optima.

The ratio of the change in the first one, over the change in the second one, of the total Gibbs energy of the packing interaction(s) and/or bond(s), as modelled about one full sweep or rotation (of the first and second intersecting planes, and/or the first and second directions of strain) in an axis orthogonal to the substrate or the surface or layer thereof, can describe (or define) the packing isotropy.

Preferably, a maximum of the ratio of the change about the one full sweep or rotation is less than 15 (more anisotropic), more preferably less than 5 (anisotropic), and most preferably less than 2 (tending toward perfect isotropy).

Lower values of the maximum of the ratio are preferred for lower selected values of the total Gibbs energy of the packing interaction(s) and/or bond(s).

It can be seen that the packing isotropy can relate to the preferred rotational symmetry and/or the preferred interactional symmetry(s). In particular, more isotropic (or less anisotropic) values of the maximum of the ratio preferentially form layers of the molecule(s) or molecular specie(s) as opposed to lineal structures.

Said differently, the population is preferably provided as a layer. More preferably, the population layer is a monolayer (or a self-assembled monolayer).

The (preferred) monolayer can be further favoured by controlling a molarity of the molecule(s) or molecular specie(s) on the substrate, and/or by controlling an environment of the deposition, and/or by controlling the annealing.

The (preferred) monolayer can also be favoured through the selection of constituent atoms or structures of the molecule(s) or molecular specie(s) in the population.

For example, the (preferred) aromatic ring(s) of the macrocycle adjuncts that are disposed in a (preferred) orthogonal configuration(s) relative to the plane of the macrocycle (or the plane of X _f , X _g , X _h, and X _f ), can tend to (or be configured to) favour a formation of the preferred monolayer (e.g. when provided to each, or substantially each, or a substantial number, of the population), and in particular when the planes of the corresponding macrocycles (or the corresponding planes of X _f , X _g , X _h , and Xi) are provided with (or tend to have) corresponding orientations that are each parallel or substantially parallel to the substrate or the surface or layer thereof (e.g. by means of the tethering interaction(s) and/or bond(s); whether by physisorption and/or chemisorption).

Said differently, when the total Gibbs energy of packing interaction(s) and/or bond(s) is divided into a first component portion having directional components that are parallel with the substrate or the surface or layer thereof, and a second (reciprocal) component portion having a directional component that is orthogonal to the substrate or the surface or layer thereof, an energetic magnitude of the first component portion that is greater than (or substantially greater than) that of the second component portion, e.g. by a factor of greater than 1-5 (or greater than 2-5), can tend to favour formation of the preferred monolayer. Relatedly, a (preferred) value of the total Gibbs energy of the tethering interaction(s) and/or bond(s) that is higher than the total Gibbs energy of packing interaction(s) and/or bond(s), can also tend to favour formation of the preferred monolayer.

The preferred population layer or monolayer, and/or the preferred high value(s) of the degree(s) of ordering or packing (and/or the previously described preferences thereof, or associations or involvements therewith), can (advantageously) tend to align (or preferably substantially align) the plurality of the molecular dipole moments in the population, and/or tend to increase a magnitude of the vector sum of the plurality of the overall net electric dipoles in the population Sm, and/or tend to increase a magnitude of the vector sum of the plurality of the dipole changes in the population SD m (in particular, when the electrically mediated bias is used to trigger or mediate or cause the inversion(s) across e.g. each, or substantially each, or a substantial number of the singular one or population).

These advantage(s) can enhance an ability of e.g. an electrical or electronic device to harness the functions of the molecule or molecular specie. Relatedly, the spatial ordering and packing (in particular, a one thereof that mediates a high degree of the preferred alignment of the molecular dipole moments in the population) is preferably provided such that these advantage(s) accrue in a time-invariant (or substantially time- invariant) manner, and/or independently (or substantially independently) of an activation of the means of forming the externally applied electric field (as can be a tendency of e.g. some ones of the preferred invertible-dipole-in-a-box configuration of the molecule or molecular specie).

The singular one or population that is preferably constrained by the substrate, and the particularly preferred population layer or monolayer or self-assembled monolayer thereof, is preferably comprised of one(s) of the molecule(s) or molecular specie(s) (whether each, or substantially each, or a substantial number of the singular one or population) of which the corresponding direction(s) of the corresponding overall net electric dipole(s) m (for at least one of the first and second isomers or conformers, but most preferably both) are aligned orthogonal, or substantially orthogonal, to the substrate or the surface or layer thereof, when so constrained (hereafter conveniently referred to as the preferred substrate-orthogonal dipole moment).

The preferred substrate-orthogonal dipole moment said differently, an (acute) angle formed between a corresponding axis(s) that is orthogonal to the substrate or the surface or layer thereof (or to an adjacent or nearby conductor or plate for forming an electric field), and the corresponding vector component(s) of the corresponding overall net electric dipole(s) m (for at least one of the first and second isomers or conformers, but most preferably both), is preferably less than 40°, more preferably less than 25°, and most preferably less than 15°, for each, or substantially each, or a substantial number of, the singular one or population.

The preferred substrate-orthogonal dipole moment can (advantageously) minimise or prevent a loss of a positional fidelity within and/or a related responsiveness of, a given one of the predetermined spatial confine (e.g. due to a migration of the constrained molecule(s) or molecular specie(s) out of the pre-determined spatial confine when the means for forming the externally applied electric field is activated, e.g. as in an STM addressing application, or when the externally applied electric field is mediated by a conductive one of the substrate or by another layer or surface that is conductive and aligned parallel thereto); and/or minimise a value of the total Gibbs energy of the tethering interaction(s) otherwise preferred for ensuring the positional fidelity and/or related responsiveness; and/or maximise a responsiveness per mole to the electrically mediated bias for a pre-determined magnitude of the externally applied electric field (or otherwise enhance an ability of e.g. an electrical or electronic device to harness the functions of the molecule or molecular specie).

For selections of the molecule or molecular specie wherein the overall net electric dipole m (for at least one of the first and second isomers or conformers, or more particularly both), is aligned more orthogonal than parallel to the plane of the macrocycle (or the plane of X _f , X _g , X _h , and Xi), or said differently an (acute) angle formed between the macrocycle axis and the vector component of the overall net electric dipole m is less than 45° (hereafter conveniently referred to as the macrocycle- orthogonal dipole moment), the means for translational and/or rotational constraint(s) preferably constrain(s) the plane of the macrocycle (or the plane of X _f , X _g , X _h, and X _f ) to be parallel or substantially parallel to the substrate or the surface or layer thereof, whereby the preferred substrate-orthogonal dipole moment is provided. These are the more preferred selections and are favoured by a number of the B ₂ OF ₂ porphyrins as previously discussed.

For selections of the molecule or molecular specie wherein the overall net electric dipole m (for at least one of the first and second isomers or conformers, or more particularly both), is aligned more parallel than orthogonal to the plane of the macrocycle (or the plane of X _f , X _g , X _h , and Xi), or said differently an (acute) angle formed between the macrocycle axis and the vector component of the overall net electric dipole m is more than 45° (hereafter conveniently referred to as the macrocycle-parallel dipole moment), the means for translational and/or rotational constraint(s) preferably constrain(s) the plane of the macrocycle (or the plane of X _f , X _g , X _h , and Xi) to be orthogonal or substantially orthogonal to the substrate or the surface or layer thereof, whereby the preferred substrate-orthogonal dipole moment is provided.

The latter selection tends to prefer a greater lateral density in the population to minimise or prevent lateral motions of the molecules or molecular species along the substrate or the surface or layer thereof, and a greater value of the total Gibbs energy of packing interaction(s) and/or bond(s) (in particular, in a component direction parallel to the corresponding macrocycle axes) can be particularly preferable.

The person skilled in the art will recognise that a number of the previously described considerations can guide or be used to determine the selected means for translational and/or rotational constraint(s), and in particular the selected tethering interaction/ s) and/or bond(s) (whether involving physisorption and/or chemisorption).

By way of summary, these considerations can (inter-relatedly) include the selection of constituent atoms or structures of the molecule or molecular specie (or relatedly the configuration thereof, e.g. the preferred invertible-dipole-in-a-box configuration), the selected means of providing the preferred substrate-orthogonal dipole moment, the selected spatial ordering or packing, the selected magnitudes and/or directionalities of the (total) Gibbs energy(s) of the tethering interaction(s) and/or bond(s) and/or of the packing interaction/ s) and/or bond(s), the selected substrate, the selected deposition, and/or the selected annealing; as well as application- specific factors including the selected pre-determined spatial confine and period of time, and the selected ones of the usable features of the molecule or molecular specie.

The means for translational and/or rotational constraint(s) preferably include(s) or involve(s) providing the molecule or molecular specie (whether as a part of the macrocycle and/or the macrocycle adjuncts, and/or as additional atom(s) or structure(s) or group(s) or moiety(s) interacted thereupon or bonded thereto, e.g. by hydride substitution or another reaction) with at least one reactive or tethering or otherwise interact-able group(s) that can interact or bond with the substrate, or otherwise form a one of the tethering interaction(s) or bond(s), for constraining each corresponding one(s) of the singular ones or population to the substrate (hereafter conveniently referred to as the reactive group(s)).

Preferably, at least one (but more preferably at least two, or each) of the reactive group(s) is/are provided with or include(s) additional spacing or linking atom(s) or structure(s) (being additional to those minimally required by the corresponding tethering interaction(s) or bond(s)) that elevate the macrocycle (and/or the macrocycle adjuncts) above the substrate by at least an additional 1A, more preferably at least an additional 2A, and most preferably at least an additional 3 A (advantageously, for providing a clearance of the molecule or molecular specie, and in particular the invertible dipole from e.g. localised defects on the substrate).

Preferably, the reactive group(s) is/are selected from those listed in Table 1 below (and/or thiol, hydroxyl, or vinyl groups). More preferably, the reactive group(s) is/are selected from the annealable reactive groups as introduced in Table 1 below. Most preferably, the reactive group(s) are thiol or hydroxyl groups.

Table 1 below sets out representation(s) of preferred selection(s) of the reactive group(s) for the molecule or molecular specie, and examples of corresponding linkage(s) formed with the selected substrate by each one of the represented reactive group(s). Abbreviations are listed in IUPAC approved form, with the substrate represented by‘sub.’ The represented reactive groups are conveniently classified as one(s) of either annealable reactive groups, or as non-annealable reactive groups.

Annealable Non-annealable

Reactive group Resulting linkage Reactive group Resulting linkage

-0(H)®sub , - -(CH ₂ ) ₂ -sub, -

-OH -CH=CH ₂

O-sub CH(Me)-sub

-CO ₂ H -C(0-sub) ₂ -CºCH -(C-C)(— sub)i _-4

-SH -S-sub -N ₃ -NH(-sub) ₂ , -N(-sub) ₃

R ^X R ² R ³ N R ¹ R ² R ³ N^sub [-NMeCH=CH ₂ ] ⁺ -NHMeCH ₂ CH ₂ -sub

-N H ₂ -N H ₂ _n(-Sub) _n -CH=N2 -CHi ₂ -sub

-OSiCI ₃ -0-Si(0-sub) ₃

-SiMe _n (OH) _3-n -SiMe _n (0-sub) _3-n

Table 1

For selections of the molecule or molecular specie that have a one of the macrocycle- orthogonal dipole moment, the means for translational and/or rotational constraint(s) (or more particularly, the means for rotational constraint(s)) preferably include(s) or involve(s) at least two ones of the reactive groups.

More preferably, the means for rotational constraint(s) preferably include(s) or involve(s) (at least) two ones of the reactive groups that are spaced apart (or

substantially spaced apart) from one another on the molecule or molecular specie by (at least) one corresponding minimum separation distance of at least 4A, more preferably at least 8 A, and most preferably at least 12 A (for advantageously providing a molecular torque).

Most preferably, (at least) two of the reactive groups that are spaced apart (or substantially spaced apart) by the (at least) one corresponding minimum separation distance each have a Gibbs energy of association/disassociation with/from the substrate of at least 40 kJ mol ¹ , and more preferably at least 50 kJ mol ¹ . The above preferences said differently, (at least) two of the reactive groups that are spaced apart (or substantially spaced apart) by the (at least) one corresponding minimum separation distance, each preferably have a magnitude of the Gibbs energy of association/disassociation with/from the substrate, multiplied by the corresponding (at least) one minimum separation distance, of at least 150 A-kJ mol ¹ , more preferably at least 300 A-kJ mol ¹ , and most preferably at least 600 A-kJ mol ¹ .

Said differently again, the means for rotational constraint(s) preferably include(s) or involve(s) (at least) two ones of the reactive groups that are disposed on opposite or substantially opposite sides of the macrocycle from one another.

Also preferably, the reactive group(s) is/are selected to provide the molecule or molecular specie (when so constrained to the substrate) whereby the plane of the macrocycle (or the plane of X _f , X _g , X _h , and Xi) is parallel or substantially parallel to the (corresponding) plane of the substrate or of the surface or layer thereof.

For selections of the molecule or molecular specie that have a one of the macrocycle- parallel dipole moment, the means for translational and/or rotational constraint(s) preferably include(s) or involve(s) at least one of the reactive groups, more preferably only one of the reactive groups, and most preferably only one of the reactive groups that is disposed (or substantially disposed) on an axis that is orthogonal to the substrate or the surface or layer thereof, and that passes through the macrocycle axis.

In an alternative preference for the selection of the reactive group(s) for a one of the population layer or monolayer, the reactive group(s) is/are selected to provide a physisorption onto the substrate during the deposition, with or without a (concurrent or subsequent) one of the annealing but preferably with, followed by a chemisorption (preferably using the non-annealable reactive group(s) as listed in Table 1 above, and/or preferably using ones of the reactive group(s) that form one or more covalent bond(s) with the substrate).

Depending upon the considerations that can guide or determine the selected means for translational and/or rotational constraint(s) (e.g. as previously discussed), the molecule or molecular specie (or the invertible dipole-in-a-box), and in particular the reactive group(s) for constraining the molecule or molecular specie to the substrate, can have the structure(s)/configuration(s) represented in Figs 8 & 9 where Fig. 8 shows a representation of the means for translational and rotational constraints, and in particular the reactive groups, when the molecule or molecular specie is provided as a B ₂ OF2-tetraarylporphyrin (or a proto-typical one thereof), in particular having four aryl groups as meso substituents for the macrocycle adjuncts, and having thiol (SH) groups as the reactive groups for forming the tethering interactions or bonds to the substrate (being a surface or layer of Au).

In Fig. 8 A the molecule or molecular specie is represented as a stick model, illustrating that each of the thiol groups are bonded to opposing ones of the heterocyclic organic ring structures that form the (tetra-dentate) parent structure of the porphyrin. In Fig 8B the molecule or molecular specie is represented as a stick model bonded to the substrate, illustrating the clearance provided by the macrocycle adjuncts and the reactive groups when interacting with or bonded to (or chemisorbed to) the substrate. The total Gibbs energy of the tethering interactions or bonds in this system is about AAG^ = 100 to 110 kJ mol ¹ . In Fig. 8C the molecule or molecular specie is represented as a space-filling model, illustrating the population when provided as the monolayer (having the spatial ordering or packing) of four ones of the molecule or molecular specie, in particular three of one isomer or conformer, and one of another isomer or conformer.

In Fig. 9 there is a shown a representation of the means for translational and rotational constraints, and in particular the reactive groups, when the molecule or molecular specie is provided as a B ₂ OF2-hexaaryl-dioxaporphyrin (or a proto-typical one thereof), in particular having two aryl groups as opposing meso substituents and four aryl groups as b-substituents for the macrocycle adjuncts, and having hydroxy (OH) groups on the two opposing aryl groups as the reactive groups for forming the tethering interactions or bonds Fig. 9A shows the molecule or molecular specie is represented as a stick model, illustrating that each of the hydroxy groups are bonded to opposing ones of the heterocyclic organic ring structures that form the (tetra- dentate) parent structure of the dioxaporphyrin. Fig. 9B is a stick model and Fig. 9C is a space-filling model): The population is provided as the monolayer (having the spatial ordering or packing) of two ones of the molecule or molecular specie. The total Gibbs energy of the tethering interactions or bonds in this system is about AAG^ =

110 to 130 kJ mol ¹ when bonded to Si or a type-B metal.

As recognised in the art, the selection of the substrate particularly (and inter-relatedly) depends upon the selection of the reactive group(s).

Preferably, the substrate is comprised of Si, or Au or another class-B metal, being a metal whose atom (or ion thereof) preferentially bonds or coordinates (or combines) with ligands that containing ligating atoms other than the lightest of the corresponding periodic group of the metal (e.g. Pd, Rh, and Pt, or Pb).

Preferably, the surface or layer of the substrate is planar or substantially planar on an atomic scale, or on a nano scale, or on a scale that corresponds to, or substantially corresponds to, or is within a factor of ten of, a maximum diameter of the macrocycle or of the macrocycle when provided with the macrocycle adjuncts.

Preferably, the deposition of the single one or population (advantageously) involves a solution phase method. Preferably, when the molecule(s) or molecular specie(s) is provided as the population layer, the solution phase method involves a spin coating method, or a roll-to-roll printing method, or an inkjet printing method, or a micro stamping method, onto the substrate.

Preferably, when the reactive group(s) is/are provided for chemisorption onto the substrate (AAG ^: >48kJ per mole of reactive group), the deposition and the annealing (if any) precede(s) a solution treatment for the chemisorption. A boronation for providing the macrocycle with the invertible dipole (or another reaction or coordination for providing another one of the invertible dipole structure) can potentially be performed in situ subsequent to the chemisorption of the molecule(s) or molecular specie(s) (less the invertible dipole).

In another preference to previous descriptions for providing the population layer constrained to the substrate, the population (or sub-populations thereof) is not provided as a monolayer, but as a poly-layer or crystal. In a preferred first step or stage toward forming the poly-layer or crystal, an initial one of the monolayer on the substrate is first formed. The initial monolayer acts as a template or seed for the formation of a second (and subsequent) layer(s) to form the poly-layer or crystal.

In one preference of the first step, the initial monolayer is provided by adsorption or physisorption onto the substrate. In another preference of the first step, the initial monolayer is provided in particular by chemisorption onto the substrate. In each of these preferences, the substrate and the molecule or molecular specie are selected to favour the applicable adsorption and/or physisorption and/or chemisorption.

Moreover, the preferred‘box’ configuration of the molecule or molecular specie, and relatedly the preferred rotational symmetry can (advantageously) promote (or be used to promote) tessellations that favour formation of the poly-layer or crystal.

During the deposition and/or the annealing generally, it is preferred to apply a pre determined electric field through the substrate to promote a pre-determined or desired one of the spatial ordering or packing, and in particular for ones of the molecule(s) or molecular specie(s) that are selected to provide ones of the macrocycle-orthogonal dipole moment that are substantially so orthogonal (within e.g. 15°), and ones of the macrocycle-parallel dipole moment that are substantially so parallel (within e.g. 15°).

In another preference to previous descriptions for providing the population with a desired configuration of the spatial ordering or packing, and a desired value of the degree(s) thereof, the molecule(s) or molecular specie(s) is/are otherwise crystallised by means known in the art and then suitably constrained and used for a bulk quality (e.g. as a nano-crystalline or micro-crystalline bulk material, having a sum of the molecular dipole moments therein).

Applications

The molecule or molecular specie according to preferred embodiments when spatially constrained (for convenience, exemplified hereafter as the invertible-dipole-in-a-box when tethered to the substrate) exhibits a number of the functions previously referred to.

By way of summary, these functions arise in particular from the two-state capability, the associated state transition characteristics (in particular, the Gibbs energy barrier(s) to the reversible transition), the electrically mediated bias in the state transition characteristics, the thermal stability, and relatedly a temperature dependence in the state transition, which lend to a range of recognisable electrical and electronic behaviours for exploitation by devices therefor.

For example, the tethered-invertible-dipole-in-a-box when provided as an insulating layer between two proximate and conductive ones of the substrate, and having a capability for the vector sum of the dipole changes ådp (regardless whether the individual vectors of the dipole changes Dm are orderly or disorderly), to provide a capacitance for energisation by an electric field applied therebetween, and a subsequent de-energisation.

More particularly, the tethered-invertible-dipole-in-a-box when so provided can function akin to a ferroelectric element, and in particular can exhibit a hysteresis associated with the Gibbs energy barrier(s) to the reversible transition (a curvature of the hysteresis relating to the degree(s) of ordering or packing, and an associated distribution in alignments of the molecular dipole moments to the electric field).

The hysteresis and an associated voltage-dependent capacitance enables use of the element e.g. in a manner akin to a tuneable capacitor or varcap (particularly for wider distributions in the alignment of the molecular dipole moments), or in a manner akin to a molecular flip-flop or a molecular switch or a memory cell or a non-volatile FRAM-like element (particularly for narrower distributions in the alignment of the molecular dipole moments). The latter applications are particularly suited for example to B ₂ OF ₂ -porphyin variants that tend to exhibit the preferred substrate-orthogonal dipole moments and can be provided as the monolayer for addressing by e.g. a scanning tip.

A switchable state (whether as a bulk property or a preferred ordered/aligned property) can be‘written’ by the application of a relatively strong magnitude of the electric field, and‘read’ through a relatively low AC voltage or weak magnitude of the electric field (An example circuit is illustrated in Figure 10 below). Symmetry in the two state capability (double well symmetry at zero magnitude of the electric field) can render the molecule or molecular specie particularly amenable to these

applications.

Fig. 10 illustrates an example circuit for manipulating and/or interrogating a state of a memory cell or device made using the molecule or molecular specie (e.g. the tethered- invertible-dipole-in-a-box) .

Other known behaviours of a ferroelectric-like element can be utilised, and in particular the molecule or molecular specie is capable of very fast state transition kinetics that are potentially amenable to being operated in the GHz to THz ranges (or nano- second operations) depending upon circuit slew rates.

However, the thermal applications that are of significant interest are those relating to the thermal stability and the related temperature dependence in the state transition. In particular, the rationale for the molecule or molecular specie is amenable to a wide selection of the Gibbs energy barrier(s) to the reversible transition, and a wide selection of the distribution in alignments of the molecular dipole moments to the electric field.

Any singularity or plurality thereof (whether providing time-dependent and/or substantially discrete thermal dependencies) can provide a single-threshold, or multi threshold, or time-dependent, or «-threshold/time-dependent, temperature-dependent sensor, being activated or state-changed by pre-determined threshold(s) of

temperature and/or a pre-determined function(s) of exposure time by temperature. The temperature-dependent sensor can be initially‘written’ and later‘read’ by an electrical or electronic device (and/or the state changes electronically or

computationally de-convoluted) to determine a thermal history of the molecule(s) or molecular specie(s) in a pre-determined timeframe.

In a preferred use of the molecule or molecular specie according to preferred embodiments of the invention a temperature monitoring element is provided. Here, a substrate is provided to carry the molecule or molecular specie whereby the molecule or molecular specie is selected such that inversion of the BOB bridging structure and macrocycle are selected such that the thermal energy corresponding to an environmental temperature is sufficient at a predetermined temperature to invert the bridging structure in a manner that is not reversible without application of an applied electric field.

In this way, the substrate preferably non-conductive and has the molecule or molecular specie adhered to it by any conventional means such as spraying, printing or stamp impregnating. A protective cover layer can be applied eg as a film or spray coating. An externally applied electric field can be used to initialise the direction of the bridging structure of each molecule. In response to exposure to a predetermined temperature the bridging structure will change direction. At a bulk scale, the temperature monitoring element can then be read by an applied electric field to determine the orientation of the bridging structures. If a sufficient predetermined number of those bridging structures has changed state then this can be measured by applying an electric field. Of course, the temperature monitoring element can be reset by the application of an electric field that significantly exceeds that required to read the state of the molecule or molecular specie on the substrate.

In another use of the molecule or molecular specie, a preferred embodiment can be applied as the ferroelectric-like element illustrated in Figure 11 where there is shown an example circuit for an element that exploits the ferroelectric -like property of the molecule or molecular specie.

In connection with the foregoing, general advantages can include that the molecule or molecular specie can be readily synthesised (in particular, amenable to modern engineering/fabrication methods), relatively inexpensive (in particular, does not include exotic elements), chemically stable (in particular towards water, oxygen, and redox reactions e.g. during synthesis, device fabrication, and device operation), can have perfect or at least near-perfect transition characteristics with relatedly minimal degradation (anticipated to sustain in excess of 10 read/write cycles), can be thermally stable at typical operating temperatures and voltages, and can be amenable to flexible and/or printable circuitry.

Examples Preferred examples of structure(s) and configuration(s) of the molecule or molecular specie have already been provided in each of Figures 6 and 7 (generally‘non- tethered’), and also Figures 8 and 9 (generally‘tethered’) although described therein with further reference to particular aspects.

Further examples of preferred embodiments of the invention are provided in Fig. 12 to 28. Particularly, Fig. 12 shows Dur ₄ -bp (porphyrin-type system): archetypal non- tetherable one of the invertible-dipole-in-a-box system. One isomer in respect of the macrocycle adjuncts.

Fig. 13 shows Xyl ₄ -bp (porphyrin-type system): a variation on Dur ₄ -bp (Figure 12) for altered packing behaviour. One isomer in respect of the macrocycle adjuncts.

Fig. 14 illustrates Dur ₂ -xyl ₂ -bp (porphyrin-type system): a variation on Dur ₄ -bp (Figure 12) and Xyl ₄ -bp (Figure 13) for more disordered packing behaviour. Two isomers in respect of the macrocycle adjuncts that are not readily separated (2+2 synthesis).

Fig. 15 is Xyl ₂ -MeSty ₂ -bp (porphyrin-type system): tetherable through vinyl groups for covalent attachment to an H-passivated Si surface, for more disorderly packing or relatedly for higher temperature annealing methods. Potential use as the (monolayer) template for layer deposition of Xyl ₄ -bp (Figure 13). Two isomers in respect of the macrocycle adjuncts (2+2 synthesis).

Fig. 16 is Xyl ₄ -bp-(SH) ₂ (porphyrin-type system): tetherable through thiol groups for covalent attachment to type-B metals, and for more orderly formation of the monolayer through metal-thiol mobility. Two isomers in respect of the macrocycle adjuncts (2+2 synthesis).

Fig. 17 shows Xyl ₄ -bp-(OH) ₂ (porphyrin-type system): tetherable through hydroxyl groups for covalent attachment to type-A metals, and for formation of the monolayer. Two isomers in respect of the macrocycle adjuncts (2+2 synthesis). Fig. 18 is Xyl ₂ -bp (porphyrin-type system): compact. Substitutable to provide tetherable variants. Two isomers in respect of the macrocycle adjuncts (2+2 synthesis).

Fig. 19 is Xyl ₂ -diazabp (porphyrin-type system): compact. Substitutable to provide tetherable variants. A high value of the Gibbs energy barrier to the reversible transition (2+2 synthesis).

Fig. 20 shows Xyl ₂ -bp-dione (porphyrin-type system): compact. Substitutable to provide tetherable variants. A higher throw or magnitude of the net electric dipole. No clear evidence of coordination isomerism (2+2 synthesis).

Fig. 21 is a Porphyrin-type system. Tetherable for providing the monolayer, and in particular for an ordered form of the self-assembling monolayer. No clear evidence of coordination isomerism (2+2 synthesis).

Fig. 22 is ROT-Xyl ₄ tBu4 _b pz (porphyrazine-type system): Uncomplexed macrocycle with the rotational symmetry. Xylyl groups in b-pyrrolic positions. Single complexed isomer.

Fig. 23 is C ₃ -Xyl ₄ tBu4 _b pz (porphyrazine-type system): Uncomplexed macrocycle with a C _s rotational symmetry. Xylyl groups in b-pyrrolic positions. Two complexed isomers for separation.

Fig. 24 shows Anthra^DA-bpz (porphyrazine-type system): Synthesized from an anthracene Diels-Alder adduct. A high level of clearance from the substrate for the invertible dipole. Tetherable groups can be incorporated into the peripheral aromatics for providing tetherable variants.

Fig. 25 is Dur ₂ -B ₂ OF ₂ -tetPy; Xyl ₂ -B ₂ OF ₂ -tetPy (X=H, Y=H); Xyl ₂ -B ₂ OF ₂ -tetPy-X (X=SH,OH,CH ₂ , Y=Me).

Fig. 26 shows Dur ₂ -C ₂ OF ₂ -tetPy; Xyl ₂ -C ₂ OF ₂ -tetPy (X=H, Y=H); Xyl ₂ -C ₂ OF ₂ -tetPy- X (X=SH,OH,CH ₂ , Y=Me). Fig. 27 is Dur ₂ -Si ₂ OF ₂ -tetPy (X=H, Y=Me); Xyl ₂ -Si ₂ OF ₂ -tetPy (X=H, Y=H); Xyl ₂ - Si ₂ OF ₂ -tetPy-X (X=SH,OH,CH ₂ , Y=Me).

Fig. 28 shows Dur ₂ -P ₂ 0 ₃ -tetPy; Xyl ₂ -P ₂ 0 ₃ -tetPy (X=H, Y=H); Xyl ₂ -P ₂ 0 ₃ -tetPy-X (X=SH,OH,CH ₂ , Y=Me)

The foregoing describes only preferred embodiments of the present invention and modifications and applications, obvious to those skilled in the art, can be made thereto without departing from the scope of the present invention.

The term“comprising” (and its grammatical variations) as used herein is used in the inclusive sense of“including” or“having” and not in the exclusive sense of “consisting only of’.

The term“structure” (and its grammatical variations) as used herein refers to a portion or moiety of a molecule or chemically-bonded entity, whether comprising a single atomic nucleus or a plurality of atomic nuclei.

APPENDIX 1

The molecule or molecule specie, and in particular the tetherable-invertible-dipole-in- a-box (e.g. of the first preferred embodiment), can be synthesised by means known in the art of macrocycles. Some generalised preferred pathways are illustrated below, followed by some useful citations and background art.

Appendix Figure 1. Preferred pathways for the synthesis of a B ₂ OF ₂ -bridged and aryl-substituted porphyrin that can provide one of the invertible-dipole-in-a-box configuration of the first preferred embodiment.

Appendix Figure 2. Preferred pathways for the synthesis of a B ₂ OF ₂ -bridged and aryl-substituted porphyrin that can provide another of the invertible-dipole-in-a-box configuration of the first preferred embodiment.

Synthesis of tetherable tetraarylporphyrins :

Jux, N. o-(Bromomethyl)-Substituted Tetraarylporphyrin Building Blocks. Org. Lett., 2 (14), 2129-2132 (2000). DOI: 10.1021/o1006028c

Huyen, N. H., Jannsen, U., Mansour, H., Jux, N.“Introducing the Staudinger phosphazene reaction to porphyrin chemistry.” J. Porphyrins Phthalocyanines, 8: 1356-136 (2004). DOI: 10.1142/S 1088424604000714

General procedures for formation of B(R)OB(R) complexed porphyrins:

Brothers, P. J. "Recent developments in the coordination chemistry of porphyrin complexes containing non-metallic and semi-metallic elements" J. Porphyrins Phthalocyanines, 6: 259 (2002). DOI: 10.1142/S 1088424602000294

Brothers, P. J. " Boron Complexes of Pyrrolyl Ligands” Inorg. Chem., 50 (24), pp 12374-12386 (2011). DOI: l0.l02l/ic20H9l9 APPENDIX 2

A mixture of 2-bromo-l,3-dimethylbenzene (1, 2 g, 10.8 mmol, CAS: 576-22-7), N- bromosuccinimide (2 g, 11.2 mmol) and benzoyl peroxide (0.1 g) is refluxed in CH ₂ Cl ₂ overnight. After cooling to room temperature, the mixture is filtered to remove excess succinimide and the filtrate containing the product is collected. The desired di-bromo product 2 is purified by column chromatography (Si0 ₂ , n-hexane 100%) with the compound isolated as a colourless oil.

1H NMR (CDCI3, 25°C, 400Hz) 2: 2.44 ( s, 3H, CH ₃ ), 4.65 (s, 2H, CH ₂ ), 7.19 (d, 2H, m-Ph), 7.29 (t, lH, p-Ph).

Synthesis of 3

Aryl bromide 2 (lg, 3.8 mmol) is added to a refluxing solution of sodium methoxide (0.41 g, 7.6 mmol) in dry methanol under N ₂ . After stirring for two hours at reflux, the mixture is cooled and the solvent removed. CH ₂ Cl ₂ is added to extract the product and the organic phase is washed with water and dried over Na ₂ S0 ₄ . The solvent is removed to yield 3 as a colourless oil.

1H NMR (CDCI3, 25°C, 400Hz) 3: 2.43 (s, 3H, CH ₃ ), 3.47 (s, 3H, OCH ₃ ), 4.65 (s, 2H, CH ₂ ), 7.19 (m, 2H, Ph), 7.29 (m, 1H, Ph).

Synthesis of 4 ¹

/7-hutyl lithiu m (2.6 mL, 2M in cyclohexane) is added dropwise to a solution of 3 (lg, 6.1 mmol) in dry Et ₂ 0 at -78°C. After stirring for two hours at this temperature, dry DMF (0.54 mL) is added dropwise and the solution is stirred for a further hour at - 78°C. The solution is warmed to room temperature and the reaction quenched by the addition of aq. NH4CI. The product is extracted with Et ₂ 0 and the organic phase is washed with water and brine, dried over Na ₂ S0 ₄ and the solvent removed to give aldehyde 4 as a pale brown oil.

1H NMR (CDCI3, 25°C, 400Hz) 4:2.64 (s, 3H, CH ₃ ), 3.45 (s, 3H, OCH ₃ ), 4.78 (s, 2H, CH ₂ ), 7.20 (m, 1H, Ph), 7.43 (m, 2H, Ph) 10.56 (s, 1H, CH).

Synthesis of 5 ²

To a 0.18 M HC1 solution (98.5: 1.5 H ₂ 0:HCl) is added pyrrole (1.17 mL, 18.2 mmol) followed by 4 (lg, 6.1 mmol) and the resulting mixture is stirred overnight under N ₂ in the dark. The mixture is filtered to yield a sticky purple solid which is then washed with water. The solid is dissolved in CH ₂ Cl ₂ and chromatographed (Si0 ₂ , CH ₂ Cl ₂ ) to give the desired product as a pale brown thick oil that slowly crystallises when stored at -l8°C.

1H NMR (CDCI ₃ , 25°C, 400Hz) 5: 2.19 (s, 3H, CH ₃ ), 3.40 (s, 3H, OCH ₃ ), 4.28 (bs, 2H, CH ₂ ), 5.97 (s, 1H, CH), 6.06 (m, 2H, b-pyrrolic), 6.26 (m, 2H, b-pyrrolic), 6.83 (m, 2H, b-pyrrolic), 7.16 (m, 3H, Ph), 8.66 (bs, 2H, NH).

Synthesis of 6 ¹

Dipyrromethane 5 (0.5 g, 1.8 mmol) and mesitylaldehyde (0.26 mL, 1.8 mmol) were dissolved in 300 mL of CH ₂ Cl ₂ containing 3 mL of EtOH. The resulting solution is purged with N ₂ for 30 minutes. BF ₃ Et ₂ 0 is added and the solution stirred for one hour in the dark. DDQ (0.61 g, 2.7 mmol) is added and the reaction stirred for a further hour. The reaction mixture is concentrated to 10 mL and passed through a plug of Si0 ₂ which is eluted with CH ₂ Cl ₂ :Et ₂ 0 19: 1 to give a bluish mixture containing the porphyrins. Further column chromatography (Si0 ₂ , CH ₂ Cl ₂ ) yielded the desired porphyrins, the first band containing 6-ab and the second containing 6-aa.

1H NMR (CDCI ₃ , 25°C, 400Hz) 6-ab:8.63 (d, 4H, b-py), 8.58 (d, 4H, b-py), 7.76 (d, 2H, Ph), 7.72 (t, 2H, Ph), 7.53 (d, 2H, Ph), 7.27 (s, 4H, Ph), 3.92 (s, 4H, CH ₂ ), 2.78 (s, 6H, OCH ₃ ), 2.62 (s, 6H, CH ₃ ), 1.90 (s, 6H, CH ₃ ), 1.85 (s, 12H, CH ₃ ), -2.51 (bs, 2H, NH).

1H NMR (CDCI ₃ , 25°C, 400Hz) 6-aa: 8.63 (d, 4H, b-py), 8.58 (d, 4H, b-py), 7.77 (d, 2H, Ph), 7.72 (t, 2H, Ph), 7.53 (d, 2H, Ph), 7.27 (s, 4H, Ph), 3.94 (s, 4H, CH ₂ ), 2.80 (s, 6H, OCH ₃ ), 2.62 (s, 6H, CH ₃ ), 1.88 (s, 6H, CH ₃ ), 1.85 (s, 12H, CH ₃ ), -2.50 (bs, 2H, NH).

The following synthesise of the boron porphyrins used the ab-6 as a test porphyrin. The reaction conditions have not been fully optimised.

Synthesis of 7-ab

BBr ₃ (0.1 mL, 0.15 mmol) is added to a solution of 6-ab (20 mg, 0.025 mmol) in dry CHCl ₃ and the mixture is refluxed for 18 hours. After cooling to room temperature, BF ₃ Et ₂ 0 (0.1 mL, 0.61 mmol) is added and the solution stirred for a further hour. The reaction is quenched by the addition of saturated aq. NaHC0 ₃ and extracted with CHCl ₃ . The organic layer is washed with water and brine and dried over Na ₂ S0 ₄ . The solvent is removed and column chromatography (Si0 ₂ , CH ₂ Cl ₂ Ch ₂ Cl ₂ :Et ₂ 0 9:1) is used to elute a red/green band containing several isomers of 7-ab.

Notes

• There are four ligation isomers of 7-ab (and of 7-aa). In TLC, you can see some separation of the isomers so it might be possible to separate them possible via HPLC if so desired. The NMR data of the bulk sample also indicates a mixture of isomers.

• Identification of 7 was achieved using mass spec which showed the parent ion peak corresponding to 7. The presence of B and F in the complex was confirmed by ^U B and ¹⁹ F NMR respectively, the chemical shifts were consistent with other B ₂ OF ₂ (Por).

Synthesis of 8-ab (and 8-aa)

A mixture of KSAc (3 mg, 0.03 mmol) and 7 (10 mg, 0.01 mmol) in dry DMF is stirred at room temperature overnight. After this time the solvent is removed and the residue purified by column chromatography (Si0 ₂ , CH ₂ Cl ₂ -> Ch ₂ Cl ₂ :Et ₂ 0 9:1) eluting a red/green band containing several isomers of 8-ab.

Notes • The B ₂ OF ₂ moiety is preserved (confirmed by ^U B, ¹⁹ F NMR and MS) in this reaction. Functionalisation at the benzylic positions with other groups could most easily be achieved at this stage under mild and basic conditions.

• As with 7, there are multiple isomers which TLC indicates can be separated.

• The AcS group is stable in air so should avoid the handling issues of thiols.

The Ac group drops off upon surface deposition on Au or is easily hydrolysed or aminolysed (under basic conditions to preserve the BOB group) if the free thiol is desired.

References

1. Huyen, N. H.; Jannsen, U.; Mansour, H.; Jux, N. J. Porphyrins

Phthalocyanines 2004, 8, 1356.

2. Rohand, T.; Dolusic, E.; Ngo, T. H.; Maes, W.; Dehaen, W. ARKIVOC 2007,

307.

3. Gryko, D. T.; Clausen, C.; Lindsey, J. S. J. Org. Chem. 1999, 64, 8635

Compounds Recovered:

6-ab: 30 mg

6-aa: 95 mg

7-ab: 5 mg

8-ab: 10 mg

Appendix 3

The following sets out figures and data derived mostly from theoretical (DFT) work into how different macrocycles compress the complexed BOB group to different degrees with the result that both the barriers to inversion and electric dipoles are significantly controlled. Whilst this largely theoretical work includes many complexes that are difficult to synthesize they are included herein to probe the parameter space and demonstrate a general principle. In preferred embodiments of the invention, BOB angles of 110° to 130° are provided but this relatively narrow range none-the-less can yield molecules with near-ideal properties for many implementations. This is supported by NMR inversion kinetics experiments on the compounds shown below (the third compound on row 1 tpFpp was not studied

Macrocycle induced compression of coordinated B-O-B groups controls the barriers to akamptisomeric inversion.

Ar = C ₆ F ₅ Ar = p-tolyl phth Meclx C6clx

X-ray crystal structures compared to DFT models. Note that crystal structures are accurate only to the limitations of the molecular mechanics force fields fit to the scattering data. Also, the packing forces in the crystals represent a significantly different“solvation environment” to that of the molecules in solution (NMR experiment).

Calculated barrier to linearity for transoid B{F)-G-B{F) macrocyc!e complexes

Ground state B-O-B angle, q f The blue curve fitted to AG ^lin (6 ) = e ^fc(180 — 1 where Q is the magnitude of the

B-O-B angle in degrees

The purple curve fitted to AG ^{lin )} — 1 where

m / Ό

16-F F-oN ₄ pc 106.62 300.4 1.430 1.372 1.322 2.247 0.397 4.16

14-F F-pc 108.89 242.7 1.431 1.375 1.323 2.283 0.363 4.19

20-F F-/-pyr 109.10 216.1 1.437 1.368 1.327 2.286 0.369 3.87

26-F F-N ₄ cl4t 111.06 181.7 1.430 1.399 1.350 2.332 0.368

21-F F-N ₂ pyr 112.07 144.5 1.458 1.361 1.335 2.304 0.359 4.84

18-F F-N _g pc 112.42 201.7 1.462 1.360 1.334 2.346 0.323 6.63

11-F F-pz 112.61 153.8 1.417 1.361 1.331 2.322 0.353 4.73

19-F F-pyr 113.07 137.6 1.409 1.363 1.329 2.313 0.345 4.63

17-F F-iN ₄ pc 113.46 182.9 1.419 1.372 1.338 2.357 0.313 7.29

9-F F-N ₂ p 114.36 140.3 1.416 1.375 1.337 2.345 0.329 4.34

10-F F-/-N ₂ p 114.78 138.5 1.413 1.374 1.335 2.347 0.323 3.79

7-F F-0 ₂ p 115.02 142.1 1.413 1.383 1.344 2.359 0.330 6.37

8-F F-/-0 ₂ p 115.83 128.5 1.410 1.374 1.335 2.358 0.313 4.25

15-F F-z-pc 116.84 91.4 ° 1.404 1.371 1.342 2.364 0.320 3.87

4-F F-p 117.19 113.7 1.411 1.377 1.337 2.379 0.296 4.19

24-F F-clx 117.65 148.6 1.410 1.397 1.348 2.402 0.293 4.46

25-F F-/-clx 119.86 89.5 1.407 1.379 1.343 2.411 0.275 3.82

5-F F-S ₂ p 121.08 91.8 1.401 1.391 1.356 2.431 0.281 4.88

27-F ^# F-N ₄ cl6t 122.60 57.5 1.410 1.416 1.370 2.479 0.266

6-F F-/-S ₂ p 123.50 64.3 1.404 1.382 1.347 2.454 0.241 3.50

28-F ^# F-N ₄ S _?C 16 123.81 88.4 1.410 1.420 1.371 2.495 0.252 30-F F-ipa, 128.26 27.4 ^b 1.413 1.417 1.391 2.547 0.234 3.68

29-F P-dipy ₂ 129.55 27.7 ^c 1.408 1.408 1.384 2.545 0.221 3.53

12-F F-Sijp 137.39 19.1 1.407 1.399 1.374 2.615 0.142 2.19

13-F F-S P 139.27 17.2 1.413 1.406 1.387 2.643 0.131 2.28

23-F F-CCpyr 152.60 7.2 1.386 1.386 1.374 2.694 0.054 1.88

22-F F-CCdipy ₂ 180.00 0.0 1.400 1.400 1.400 2.803 [0] [0]

* first order TS barrier 87.2 kJ mol-1, TS B-O-B angle : 52.28°, ^# figures for lower energy conformer, i.e. the TS is not inversion symmetric.

AG ^lin {0) = e ^{k( 180_q)} - 1 , k = 0.0763, R ² = 0.9829

- 1, k = 0.0840, b = 121.805, R ² = 0.9594

APPENDIX 4

The following is a discussion of aspects of the akamptisomerism described above and formed the foundation for the publication of the present inventor, et al in Nature Chemistry, volume 10, pages615- 624 (2018) whereby the contents and disclosure of which are expressly incorporated herein in their entirely.

A new fundamental type of conformational isomerism

Contents

51. Conceptual understanding of isomerisation . 71 a. Existing definitions from the“IUPAC Gold Book” . 71 i. isomer and isomerism . 71 ii. constitution and constitutional isomerism . 71 iii. stereoisomers and stereoisomerism . 71 iv. enantiomer and enantiomerism . 71 v. diastereomerism, diastereoisomerism, diastereoisomers and diastereomers . 71 vi. cis-trans isomers . 71 vii. rotamer and rotamerism . 71 viii. rotational barrier . 71 ix. free rotation (hindered rotation, restricted rotation) . 71 x. atropisomers and atropisomerism . 71 xi. conformer . 71 xii. conformation, conformational isomers and conformational isomerism . 71 xiii. configuration (stereochemical) . 72 xiv. polytopal rearrangement . 72 xv. pyramidal inversion . 72 b. Polytope Formalism . 72 i. Background . 72 ii. Extended Polytope Formalism: Internal Rotation and Fundamental Stereoisomerism . 72 iii. Simple processes, fundamental processes, and Bond-Angle Inversion . 73 iv. Establishing akamptisomerism as a fundamental isomerisation process involving BAI . 74

52. Synthesis and Characterisation of Isomer Fractions . 76 a. Synthesis . 76 b. Chiral HPLC Separation . 76

53. 'H, ¹³ C and ¹⁹ F NMR spectra . 77

54. ¹⁹ F NMR kinetics study of thermal isomerisation between Frl and Fr4 . 85

55. UV-Vis Absorption, Circular Dichroism, and Magnetic Circular Dichroism Spectra . 89 a. Room temperature spectra . 89 b. Low temperature spectra . 91

56. DFT Calculations . 93 a. DFT Geometries . 93 b. DFT intrinsic barriers to BAI in simple molecules . 94 c. DFT Reaction Pathways, Transition States and Reaction Rates . 94 i. DFT B-O-B Inversion (Akamptisomerisation) Transition State Energies . 94 ii. DFT B-O-B Coupled Pair of Torsions Transition State Energies . 95 iii. DFT In-plane (BF)O(BF) Rotation (Strepsisomerisation) Transition State Energies . 96 iv. DFT Fluoride Dissociation and Cationic Species Transition State Energies . 97 d. DFT Potential Energy Surface scans . 99 e. DFT 'H and ¹⁹ F NMR spectra . 100 f. DFT Absorption and Circular Dichroism spectra . 100

57. Isomer Structure Assignments . 103 a. Isomer Assignments: NMR . 103 b. Isomer Assignments: ABS, CD, and MCD . 106

58. Nomenclature . 106 a. Failings and weaknesses of existing nomenclature . 106 b. Akamptisomers and autoakamptisomer . 107 c. Strepsisomerisation and the strepsisomerisation cycle . 108 d. parvo / amplo stereodescriptors, determination and meaning . 108 e. Nomenclature for transition structures . 109 f. Listing of all species and proposed systematic names . 109

S9. Supplementary References . 115

SI. Conceptual understanding of isomerisation a. Existing definitions from the "TUPAC Gold Bonk"

Chemical terminology concerning isomerisation is defined in the“IUPAC Gold Book” ¹ . Those directly pertinent to the work presented are reproduced here:

L isomer and isomerism

One of several species (or molecular entities) that have the same atomic composition (molecular formula) but different line formulae or different stereochemical formulae and hence different physical and/or chemical properties. Isomerism is the relationship between isomers. See Ref. page 1129 and Ref. page 2210.

1L constitution and constitutional Isomerism

The description of the identity and connectivity (and corresponding bond multiplicities) of the atoms in a molecular entity (omitting any distinction arising from their spatial arrangement). See Ref. ² page 1100 and Ref. ³ page 2204 and 2205.

III. stereoisomers and stereoisomerism

Isomers that possess identical constitution, but which differ in the arrangement of their atoms in space. Stereoisomerism is the relationship between stereoisomers. See Ref. ³ page 2210.

iv. enantiomer and enantiomerism

One of a pair of molecular entities which are mirror images of each other and non-superposable.

Enantiomerism is the relationship between enantiomers. See Ref. ² page 1112 and Ref. ³ page 2207. diastereo erlsm, dlastereoisomerism, diastereoisomers and diasteree users

Stereoisomerism other than enantiomerism. Diastereoisomers (or diastereomers) are stereoisomers not related as mirror images. Diastereoisomers are characterised by differences in physical properties, and by some differences in chemical behaviour towards achiral as well as chiral reagents. See Ref. ² page 1105 and Ref. ³ page 2205.

vL eis-trans Isomers

Stereoisomeric olefins or cycloalkanes (or hetero-analogues) which differ in the positions of atoms (or groups) relative to a reference plane: in the cA-isomcr the atoms are on the same side, in the irans-isomer they are on opposite sides. See Ref. page 2204.

v!L rota user and rotameris

One of a set of conformers arising from restricted rotation about one single bond. Rotamerism is the relationship between rotamers. See Ref. ³ page 2217.

vllL rotational barrier

In a rotation of groups about a bond, the potential energy barrier between two adjacent minima of the molecular entity as a function of the torsion angle. See Ref. ³ page 2217.

lx. free rotation (hindered rotation, restricted rotation)

In a stereochemical context the rotation about a bond is called 'free' when the rotational barrier is so low that different conformations are not perceptible as different chemical species on the time scale of the experiment. The inhibition of rotation of groups about a bond due to the presence of a sufficiently large rotational barrier to make the phenomenon observable on the time scale of the experiment is termed hindered rotation or restricted rotation. See Ref. ³ page 2209.

x atropisomers and airoptsoraerism

A subclass of conformers which can be isolated as separate chemical species and which arise from restricted rotation about a single bond, e.g. ort/zo-substituted biphenyl, l,l,2,2-tetra-ier/-butylethane. Atropisomerism is the relationship between atropisomers. See Ref. ³ page 2200.

xt. confor er

One of a set of stereoisomers, each of which is characterised by a conformation corresponding to a distinct potential energy minimum. See Ref. page 2204.

xii conformation, conformational isomers and conformational Isomerism The spatial arrangement of the atoms affording distinction between stereoisomers which can be interconverted by rotations about formally single bonds. Some authorities extend the term to include inversion at trigonal pyramidal centres and other polytopal rearrangements. Conformational isomerism is the relationship between conformational isomers. See Ref. ² page 1099 and Ref. ³ page 2204.

xSL configuration (stereochemical)

In the context of stereochemistry, the term is restricted to the arrangements of atoms of a molecular entity in space that distinguishes stereoisomers, the isomerism between which is not due to conformation differences. See Ref. ² page 1099 and Ref. ³ page 2204.

xiv. polytopal rearrangement

Stereoisomerisation interconverting different or equivalent spatial arrangements of ligands about a central atom or of a cage of atoms, where the ligand or cage defines the vertices of a polyhedron. For example, pyramidal inversion of amines, Berry pseudorotation of PF5, rearrangements of polyhedral boranes. See Ref. ³ page 2213.

V OTvamtoal nv rsion

A polytopal rearrangement in which the change in bond directions to a three-coordinate central atom having a pyramidal arrangement of bonds (tripodal arrangement) causes the central atom (apex of the pyramid) to appear to move to an equivalent position on the other side of the base of the pyramid. If the three ligands to the central atom are different, pyramidal inversion interconverts enantiomers. See Ref. 3 page 2215.

I . Polytope Formalism

L Background

In order to understand the rearrangement of ligands in coordination complexes such as, e.g., PF5 and

[CoCl ₂ (NH ₃ ) ₄ ] ⁺ , the polytope formalism of molecular structure was developed ^{4 12} and has proven effective in providing a framework for understanding the relative stabilities of coordination complex stereoisomerism, and the dynamics of the stereochemical interconversions between these isomers.

The word polytope is a spatial-dimensionally general term for a (usually convex) polyhedron (the three- dimensional specific term). Thus, the zero-dimension polytope is a point, and for one- and two- dimension cases it is a line interval and polygon, respectively. Historically, the polytope formalism has been applied to:

i. Simple complexes of general formula ML , where x separate and distinct ligands L coordinate to the central atom M, for example PF5.

ii. Chelated or constrained complexes, where for ML at least two of the ligands form a single, well defined molecular unit chelated to M, leading to constraints on rearrangements.

iii. Cluster complexes of general formula M _y L _x , where the ligands L coordinate to a central polyhedral cluster of atoms M^, for example o-carborane C2B10H12.

In each case, the known structure of the complex/molecule of interest is related to an idealized polytope model depicting the structural aspects of interest. For the simple example of PF5, the F ligands about the P form a trigonal-bipyramid and this becomes the reference polytope for investigating the rearrangements of the F atoms about P. For the more complex o-carborane example, it may be the rearrangement of atoms within the icosahedral C B _m cluster with the H atoms ignored.

In mapping out all the unique pathways that the starting polytopal form can transform into the product stereoisomer, the polytope will transform or“traverse” between various geometries, usually with some other less stable polytope representing the transitions state structure(s). A key feature of the formalism is that each polytopal rearrangement will have an associated vibrational mode that corresponds to the initial displacement vectors. Rearrangements that would be confidently defined as“conformational isomerism” will have associated normal vibrational modes of low frequency (i.e. low energy) and relatively large amplitude. Other rearrangements better described as“configurational isomerism” are, by definition, relatively high energy processes and as such, their associated normal vibrational modes will be of high frequency and small amplitude.

IL Extended Polytope Formalism: Internal Rotation ami Fundamental Stereoisomerism

To date, much of the application and development of the formalism has concerned the higher

coordination numbers and cluster compounds with those ubiquitous systems of lower-dimension/lower- coordination number receiving little mention, indeed introductions to the formalism usually begin with four-coordinate systems such as the tetrahedral and square planar interconversion. However, all molecules are dynamic entities, with each distinct molecular topology exhibiting a unique repertoire of atomic motions. We reduce this complexity to its fundamental stereoisomeric elements to produce a rigorous classification facilitating the systematic investigation of chemical structure and reactivity. This involves the following premises:

1. Remaining within the strict definition of stereoisomerism whereby we limit our analysis to molecular systems with a fixed constitution and connectivity, i.e. fixed molecular topology.

2. Extending the existing polytope formalism to allow for the description of internal rotations.

3. Tabulating all distinct polytopal “traverses” (degrees of freedom) possible for a given coordination geometry including the canonical orbital hybridization changes involved.

4. Appling this extended polytope formalism in an unbiased fashion to each and every atom in the system of interest, eliminating those possible motions that would otherwise lead to a change in connectivity.

The inclusion of internal rotations into the formalism is a logical one. With the traditional polytope formalism accounting for the atomic motions immediately adjacent to the central atom of interest and connects these motions to vibrational modes, it describes all aspects of stereoisomerism except for internal rotations. Inclusion of internal rotation simply requires that those points defining the polytope be represented as entities differentiated by their orientations. Further, to describe the most general cases, all ligands are assumed to be independent of each other (non-chelating). For a system to exhibit internal rotation, a necessary requirement is for the atom of interest M, to be part of the inner definition of a dihedral angle, i.e. F-M-F'-X. Consequently, internal rotations are only possible for coordination numbers of 2 or higher. Most significantly, such internal rotations will often depend on the coordination number and geometry of the ligands F and F'.

Simple processes, iimdame al processes., amt Boad-Aegle tovers

In Supplementary Table 1 we exhaustively list the ground state stereoisomeric possibilities up to 4- coordinate species F ₄ ; in addition, the complexity and nature of stereoisomerism in higher coordination numbers is introduced by the inclusion of some 5- and 6-coordinate geometries. All species are classified in terms of their spatial dimensionality n (1 = linear, 2 = planar, etc.), their number of atomic centres, and the number of vertices in the polyhedron that encloses them. The extended polytope formalism then specifies all possible (non-dissociative unimolecular) mechanisms for isomerisation reactions amongst these possibilities. These processes we term fundamental types of stereoisomerism.

For linear MF ₂ molecules, only rotation about bonds can produce isomers. If the rotation is about a single bond, then conformational isomers result that are likely not to be isolable at room temperature. However, rotation about double bonds is well known, e.g., producing enantiomerisation of substituted allenes (CRIR ₂ )=C=(CR ₃ R4).

Our primary interest is in the results obtained for bent MF ₂ molecules. Two fundamental types of isomerisation processes are available: bond rotation again, but now also bond-angle inversion (BAI). During a BAI reaction, the angle under consideration becomes linear at or near the transition state. BAI involving double bonds is a well-known process, as discussed in the Main Text. However, the products of this type of BAI are also producible by bond rotation. While interest often concerns the question as to which mechanism provides the lowest-energy pathway, the two fundamental processes produce the same products and so only one chemical notation is required, a notation that already exists.

In principle, all fundamental isomerisation processes can produce unique products, demanding appropriate nomenclature. To date, however, there have been no reactions demonstrated producing isolable compounds for which BAI is the only available reaction descriptor and the only distinction available for compound nomenclature. Hence no fundamental isomerism process involving BAI has been identified. It is not classified as such in modern treatises of stereochemistry, ³⁵ and has no associated nomenclature in the IUPAC“Gold Book” ¹ . The polytope formalism shows that this is in principle possible, and that no other simple fundamental form of isomerisation remains to be discovered.

Elements of simple forms often reappear as polytope rearrangement processes of larger systems. Rotation about bonds is ubiquitous, as Supplementary Table 1 shows. Also, the BAI mechanism occurs as part of polytope rearrangement in the MF ₄ species with all involving the square-planar geometry: o Tetrahedral inversion via two orthogonal antisymmetric BAIs

o Square pyramidal inversion via two orthogonal symmetric BAIs

o See-saw inversion via a single BAI

In all such cases, BAI only acts in competition with other mechanisms, so that again no new notations are required with no such processes involving BAI needing to be recognized as fundamental.

iv. Establishing akampilso erls as a fundamental Isomerisation process Involving BAI

The primary purpose of this work is to isolate stereoisomers related by BAI as the only feasible fundamental isomerisation process, as this extended polytope formalism implies should exist. In this way compounds will be isolated that are not nameable using standard procedures as no nomenclature specific only to BAI currently exists. To do this we focus on akamptisomerism in which BAI occurs about single bonds in ML2 systems, an isomerisation process not yet demonstrated synthetically. External constraints to the ML ₂ unit are applied through encapsulation in a macrocyclic ligand so as to prevent the operation of other fundamental processes such as (coupled) bond rotation to make isolable, unnameable, compounds. This parallels the identification of atropisomerism as a fundamental process and demands the inclusion of new terms depicting BAI to the existing IUPAC definitions summarized in Section Sla.

Supplementary Table 1. Fundamental stereoisomerism elements, complete up to up to 4-coordinate, based on the extended polytope formalism listed by coordination number and geometry with their accompanying spatial dimension and number of atomic centres and vertices. The atomic centres, represented as spheres, are coloured to indicate orientation allowing observation of internal rotations. The“central atom” is green with ligand atoms purple.

Number of

Spatial Number

vertices in

Formula Dimension of atomic Model Stereoisomerisation mechanisms

associated

n centres

polyhedron

a: such unusual and extreme geometries rarely describe real ground state molecular systems and are suggested here for mathematical completeness and as potential transition states and excited state structures b : Other 6-centre polytopes include pentagonal-planari, pentagonal-pyramid, etc. c: Other 7-centre polytopes include haxagonal-planari, hexagonal-pyramid, etc.

S2. Synthesis and Characterisation of Isomer Fractions . Synthesis

To a solution of 5, 10, 15,20-letrakis(3,5-di-i _< v/7-butylphenyl)quinoxalino[2,3 //Jporphyrin (1) (100 mg, 0.0858 mmol) and freshly distilled EhN (0.50 mL, 3.59 mmol) in dry CH ₂ CI ₂ (20 mL) was added fresh, triply distilled BF ₃ :OEt ₂ (435 pL, 3.53 mmol) and warmed to 50°C for 1 hour. On completion, the reaction products were washed with 1 M NaOH _(aq) and the organic phase concentrated under reduced pressure. A sample was retained for chiral HPLC fractional analysis. The bulk product was purified by flash column chromatography (CH ₂ Cl ₂ /hexane/Et ₃ N, 2: 1:0.5%) giving two green polar bands (racemate A comprising Frl + Fr2) and (racemate B comprising Fr3 + Fr4). Yields: (A = Frl + Fr2) 41 mg (39%), (B = Fr3 + Fr4) 42 mg (40%). All fractions (Frl, Fr2, Fr3, Fr4) from the reaction mi ture were found in equal amounts (25.0 + 1 % of products) by chiral HPLC (see next subsection).

Room temperature ultraviolet-visible spectra were carried out using a Cary 5E UV-Vis-NIR

spectrophotometer in ethanol free chloroform that was deacidified by filtration through a column of neutral alumina. See section 3 for ¹ H, ¹³ C and ¹⁹ F NMR data.

(A = Frl + Fr2) Anal. Found: C, 78.3%; H, 7.6%; N, 6.7%. C ₈₂ H ₉₄ B ₂ F ₂ N ₆ O.H ₂ O requires C, 78.33%; H, 7.70%; N, 6.68%. UV/Vis k _max /nm 638 (logs 4.33), 589 (4.23), 549 (3.78), 462 (5.30). See S3 for 1H, ¹³ C and ¹⁹ F NMR data. mJz (MALDI-TOF) 1239 (M ⁺ requires 1238.76).

(B = Fr3 + Fr4) Anal. Found: C, 78.4%; H, 7.5%; N, 6.8%. C ₈₂ H ₉₄ B ₂ F ₂ N ₆ O.H ₂ O requires C, 78.33%; H, 7.70%; N, 6.68%. UV/Vis k _max /nm 635 (logs 4.37), 587 (4.23), 549 (3.80), 461 (5.33). See S3 for 1H, ¹³ C and ¹⁹ F NMR data . m!z (MALDI-TOF) 1239 (M ⁺ requires 1238.76). b.. Chiral I! FLC Separation

Chiral HPLC separation of the four isomers was effected with the use of a Jones Apex chiral PK analytical (Jones Pirkle type l-A) semi-prep column. The mobile phase consisted of ice-bath-chilled spectroscopic grade «-hexane/2-propanol (99: 1), filtered and degassed, at flow rates of 1.00 and 1.50 mL/m. Photometry at 420 nm was utilised. At this wavelength, all isomers demonstrated strong and essentially identical molar absorptions. Each injection volume was 100 qL of sample concentrate in neat «-hexane. Ice-bath-cooled eluted fractions were always immediately evaporated to dryness using a stream of dry N ₂ gas in order to minimise akamptisomerisation.

The four fractions (Frl, Fr2, Fr3 and Fr4) had approximate retention times listed in Supplementary Table 2. Actual retention times varied slightly depending upon variations in mobile phase temperature, column loading by different fractions and flow rate.

Fraction _ Retention time / m

Frl 19-23 Supplementary Table 2. Approximate retention times for the

Fr2 25-30 four reaction products on a Jones Pirkle type 1 -A chiral

Fr3 34-35 HPLC column.

Fr3 36-45

To obtain high purity isolates, each sample/fraction was rerun up to three times. On each initial sample run, only eluted material corresponding to the upper ¾ to ½ of each fraction’s peak was retained in order to reduce contamination. Material for each subsequent rerun was re-dissolved immediately prior to sample injection to minimise contamination due to solution phase akamptisomerisation (Frl ^ Fr4 and F2 Fr3).

Supplementary Figure 1 shows four example traces of HPLC runs at various stages of the separation process and the nature of reducible contamination at various stages of the protocol. At the end, high purity samples were obtained.

Supplementary Figure 1. Example chiral HPLC traces (a) initial separation of a racemic mixture of Frl and Fr2 as pre-purified by flash-silica chromatography. Despite the care and rigorous technical attention to exclude contamination with racemic Fr3 and Fr4, the inevitable duration that the components remained in solution during work up provides opportunity for a degree of akamptisomerisation as evidenced by the small proportion of racemic Fr3 and Fr4 that formed (b ) second-iteration isomer separation run using the partially purified Fr4 from an initial separation pass.

Clearly Fr4 was contaminated by Fr3 to the extent of approximately 2.5%. The necessary solution phase requirement for this second separation step revealed that akamptisomerism occurred to the extent of approximately 4.7%. Nevertheless , the well separated fractions in this second run facilitated extremely reliable separation of all components (c) third-iteration isomer separation run on Fr4 revealed effectively > 99.9 % purity (d) third-iteration isomer separation run as for (c) carried out on Frl demonstrated a small 0.5% contamination with its akamptisomer Fr4 which was easily removed due to the greatly spaced retention times

S3. 'H, ¹³ C and ¹⁹ F NMR spectra

All NMR spectra were recorded on a Bruker A VANCE III spectrometer equipped with either a 5 mm or 1.7mm inverse broadband probehead incorporating z-gradients ( ¹ H at 500.13 MHz, ¹⁹ F at 470.52 MHz and ¹³ C at 100.21 MHz). ¹ H and ¹³ C NMR spectra were referenced to residual solvent resonances (CHC1 ₃ 67.26 (1H) and 677.16 ( ¹³ C)). ¹⁹ F NMR spectra were referenced to external 1% TMS in CDC13 at 60.0. Sample temperatures were stabilized using a variable temperature unit (BVT2000), and the spectra presented were recorded at 250 K. Chemical shifts (6) are given in ppm. Standard pulse sequences supplied by Bruker were used to run all 1D and 2D NMR spectroscopy. All data were collected and processed using Bruker Topspin 3.5 software.

1D H NMR spectra were acquired with 64K data points over a spectral width of 10000 Hz. Data were zero filled and multiplied by an exponential apodization function prior to Fourier transform. Homonuclear 2D NMR experiments (dqf-COSY, NOESY, ROESY) were typically run using a 90° pulse of 14.4 ps (5mm probe) or 4.9 us (l.7mm probe) and a relaxation delay of 2.0 s over a spectral width of 5500 Hz using 4096 data points, giving an acquisition time of 0.37 s. Experiments were acquired over 256 increments each with 16 accumulated scans. Linear prediction of 128 Zi data points and zero filling were applied prior to transformation, giving a 4k x 4k data matrix. Shifted sine-bell window functions were applied in both dimensions. Mixing times for NOESY experiments were varied from 400 to 800 ms; ROESY experiments were carried out using mixing times ranging from 200 to 400 ms.

Heteronuclear 2D experiments ( ' H- ¹³ C HMBC, 'H- ^{i 3} C HSQC) employed parameters for the ¹ H

(acquisition) dimension as described for homonuclear experiments. For H- C experiments the C dimension utilised a 90° pulse of 10.2 ps (5mm probe) and 9.8 ps (1.7mm probe), with 400 increments collected over a spectral width of 27700 Hz with 48 scans accumulated for each increment. Data collection was optimised for coupling constants of 125 Hz (HSQC) and 8 Hz (HMBC). Data was linear predicted in the ^I3 C dimension over 128 points, and a squared sine -bell function applied. An exponential line broadening of 2 Hz was applied to the acquisition dimension and zero filling was employed in both dimensions to give a 4k x 4k data matrix.

Supplementary Figure 2 indicates the internuclear correlations used in assigning peaks. Supplementary Figures 3 and 4 show the H. ¹³ C and ¹⁹ F NMR spectra of racemate A (= Frl + Fr2) and racemate B (= Fr3 + Fr4). See S7 for isomer assignments. Supplementary Tables 3, 4 and 5 summarise these spectra.

Supplementary Figure 2. Internuclear correlations used to determine chemical shift assignments. See S7 for details of isomer assignments.

Supplementary Figure 3 continued. ¹ H, ¹³ C and ¹⁹ F NMR spectra of (Frl + Fr2). Annotations indicate peak assignments

Supplementary Figure 4. ¹ H, ¹³ C and ¹⁹ F NMR spectra of (Fr3 + Fr4). Annotations indicate peak assignments

Supplementary Figure 4 continued. ‘ H, ¹³ C and ¹⁹ F NMR spectra of (Fr3 + Fr4). Annotations indicate peak assignments Supplementary Table 3. H chemical shift assignments for racemates (FI + Fr2) and (F3 + F4) at the temperatures indicated. “Note” indicates the number of H atoms and the signal description.

(Frl + Fr2) at 260 K (Fr3 + Fr4) at 240 K

7.840 7.883 p-ArlO 1 7.855 p-Arl5, H26, 7.889 p- Ar5 1

4

7.870 H27, H28 7.910_ H26_ 1, m 7.875

H27, H28,

7.780 p-ArlO 1 7.975 3 p- Ar20

7.950 o- Ar20 1

8.030 p-Ar20 1 8.036 o-Ar5 1 8.100 o-Ar5 1 8.068 o- Ar20 1 8.110 H29 1 , m 8.182 o-ArlO 1 8.180 o-ArlO 1 8.225 o-Ar5 1 8.195 o-Ar5 1 8.228 o-Ar20 1 8.270 o-ArlO 1 8.258 H29 1, m 8.320 o- Ar20 1 8.299 o-ArlO 1 8.60 o-Arl5 1, very broad 8.636 o-Arl5 1, broad 8.665 H7 1, d 8.668 H12 1, d 8.720 H8 1, d 8.724 H17 1, d 8.925 H12 1, d 8.819 H13 1, d 9.020 H13 1, d 8.865 H18 1, d 9.035 H17 1, d 8.891 H7 1, d 9.215 H18 1, d 9.048 H8 1, d a) number of protons, m = multiple t, d = doublet

Supplementary Table 4. ¹⁹ F chemical shift assignments for racemates (Frl + Fr2) and (Fr3 + Fr4) at the temperatures indicated. “Note” indicates the number of F atoms and the signal description

_ (Frl + Fr2) at 270 K _ (Fr3 + Fr4) at 240 K

¹⁹ F d / ppm Assignment Note” F d / ppm Assignment Note ^a

-141.02 F“ 1, s -141.11 F“ 1, s

-162 71 _ _ 1, s -160.83 F ^p 1, s a) s = singlet

Supplementary Table 5. ¹³ C chemical shifts and assignments for the 50 aromatic carbons for each of racemates (Frl + Fr2) and (Fr3 + Fr4) at the temperatures indicated. “Note” indicates the number of C atoms and the signal description.

(Frl + Fr2) at 260 K (Fr3 + Fr4) at 240 K C d / ppm Assignment Note ^a

120.601 C20 1, sharp 116.317 C5 1, sharp

120.830 p-Ar20 1 120.484 C20 1, sharp

121.438 p-ArlO 1 120.914 p-Ar20 1

121.585 p-Arl5 1 121.360 p-Ar(5/10) 1

122.086 p-Ar5 1 121.695 1

123.207 C7 1 122.011 p-Arl5 1

123.652 C5/C15 1 124.218 C13 1

123.713 C5/C15 1 124.890 C17 1

125.716 C13 1 125.514 C7 1

126.278 CIO 1, sharp 126.366 CIO 1, sharp

126.539 C17 1 127.724 o-Ar20 1

128.497 o-Arl5 1, very broad 129.243 o-Ar5 1

129.807 o-ArlO 1 129.577 o-Arl5 1, very broad

129.834 C(26/27/28) 1 129.677 o-ArlO 1

130.016 o-Arl5 1, very broad 129.756 o-Ar(5/20) 1

130.056 o-Ar5 1 130.093 C29 1

130.103 C(26/27/28)/C29 1 130.231 1

130.254 C(26/27/28)/C29 1 130.415 C27/C28 1

130.297 o-Ar5 1 130.434 C27/C28 1

130.614 o- Ar20 1 130.863 C26 1

130.733 C(26/27/28) 1 131.010 o-Ar(5/10/20) 1

131.157 o-ArlO 1 131.029 o-Arl5 1, very broad

132.133 o-Ar20 1 133.866 1

135.389 1 133.882 1

136.567 1 133.961 1

136.704 C8 1 134.448 C18 1

137.170 C12 1 134.841 1

137.828 C18 1 135.430 C12 1

139.169 1 136.275 1

140.543 1 138.456 C8 1 140.800 1 140.696 1 141.130 C16/C19 1 140.714 C9 1 141.393 1 141.122 C25a/C29a 1 141.535 1 141.293 C25a/C29a 1 141.547 C14 1 144.407 C6 1 141.593 1 145.926 1 143.366 1 146.028 1 145.699 C6/C9 1 146.043 1 146.003 C16/C19 1 146.089 C11/C14 1 146.017 1 146.506 C16 1 146.285 1 146.801 C11/C14 1 146.607 1 147.759 1 147.919 1 148.083 1 148.227 1 148.667 1 148.310 1 149.277 1 149.355 1 149.298 1 149.397 1 149.380 1

149.544 1 149.985 C19 1 149.996 C6/C9 1 150.555 1 150.752 1 151.089 1 a) number of carbons

S4. ¹⁹ F NMR kinetics study of thermal isomerisation between Frl and Fr4

Highly purified samples of Frl were dissolved in CDCl ₃ prior to ¹⁹ F NMR measurements on a Bruker AVANCE I spectrometer (282 MHz; CF3CI). Temperature was controlled using a Bruker B-VT 2000 variable temperature unit. NMR spectra were taken at regular time intervals as shown in Supplementary Table 6, with the signal for Frl decreasing and that for Fr4 (see Supplementary Figure 5)

correspondingly increasing. A time history of the NMR spectrum measured at different sample temperatures is shown in Supplementary Figure 6. The rate of akamptisomeric equilibration was determined by following the evolution of the ratio of the peak area at dr = - 162.7 ppm to the total peak areas at 6F = -160.8 ppm and 6F = -162.7 ppm with the results summarised in Supplementary Table 6 and kinetics profiles shown in Supplementary Figure 7. Error estimates are based on signal to noise ratios for each measurement.

The equilibration rate was determined at five temperatures between 298 K and 323 K as shown in Supplementary Table 6Supplementary Table and an Arrhenius plot constructed (Supplementary Figure 8) to determine an activation energy of 104 ± 2 kJ mol ¹ .

Supplementary Table 6. Summary of ¹⁹ F NMR relative peak areas at various temperatures and inspection interval times with their calculated reaction rate constants k.

Relative i area at time:

Temperature / K - ^— _

0 mm 40 min 80 min 120 min 160 min 240 min note ⁴

298 [1] ± 0.01 0.96 ± 0.01 0.93 ± 0.01 0.90 ± 0.01 7.8

308 [1] ± 0.01 0.93 ± 0.01 0.87 ± 0.01 0.82 ± 0.01 31.1

313 [1] ± 0.02 0.88 ± 0.02 0.79 ± 0.01 0.72 ± 0.01 57.0

318 [1] ± 0.01 0.80 ± 0.01 0.68 ± 0.01 0.60 ± 0.01 109.9

323 [1] ± 0.02 0.69 ± 0.02 0.57 ± 0.02 0.53 ± 0.02 198.5 a: Area(-162.7 ppm)/{Area(- 162.7 ppm) + Area(-160.8 ppm) } b: Rate constant determined by assuming k = k = k. _\ whereby it follows that the relative concentration of Frl at time t is described by [Frl], = [Frl] (1 + e ^{-2 k t} ).

-125 -130 -135 -140 -145 -150 -155 -160 ppm

Supplementary Figure 5. ¹⁹ F NMR spectrum of Fr4, chemical shifts relative to CF ₃ CI.

Supplementary Figure 6. Raw ¹⁹ F NMR traces at various times and temperatures determined in CDCfi.

0 2000 4000 0000 8000 10000 12000 14000

4 / S

Supplementary Figure 7. Fitted first order reaction rate profiles corresponding to the data and temperatures as shown in Supplementary Table 6. The dashed line indicates the asymptotic equilibrium concentration of 0.50 ± 0.02 indicating nearly isoenergetic products i.e. AGs - AG2 = 0.0 +0.2 kJ mol ¹ .

Supplementary Figure 8. Arrhenius plot for the first order rate constants at temperatures as shown in Supplementary Table 6 and Fitted first order reaction rate profiles corresponding to the data and temperatures as shown in Supplementary Table 6. The dashed line indicates the asymptotic equilibrium concentration of 0.50 ± 0.02 indicating nearly isoenergetic products i.e. AG3 - AG2 = 0.0 ±0.2 kJ mol-1.

The fitted activation energy is

104 +2 kJ mol ¹ . S5. UV-Vis Absorption, Circular Dichroism, and Magnetic Circular Dichroism Spectra

Ro mi temperature s ectra

Room temperature ultraviolet-visible spectra were measured using a Cary 5E UV-Vis-NIR

spectrophotometer in ethanol-free chloroform that was deacidified by filtration through a column of neutral alumina.

Room temperature (298 K) simultaneous absorption (ABS) and circular dichroism (CD) were recorded on a Jasco J-810 CD spectrometer between 700 nm and 400 nm at 1 nm increments, 20 to 50 accumulations, 200 nm/m, response time 0.25 s, 0.5 nm band width and a sensitivity of 0.05°. The quartz sample cell had a path-length of 10.0 mm. The solvent used was 2-methyltetrahydrofuran (2-MeTHF) (Sigma-Aldrich, anhydrous, > 99.0%), redistilled and filtered through dried neutral alumina. The porphyrin samples used were freshly prepared by chiral HPLC and estimated to be of > 99.9 % purity. Supplementary Figure 9 and Supplementary Figure 10 show spectra for Frl and Fr4, respectively, observed using a range of sample concentrations in the 5-20 mM region. The spectra of Frl and Fr2 were not significantly different from each other except for a sign reversal of the CD, indicating that these fractions are enantiomers, and hence spectra are shown only for Frl. Similarly, Fr3 and Fr4 are also enantiomers. The spectra show little variation with solvent and concentration, indicating that the intrinsic CD of isolated molecules is being measured rather that the CD of oligomeric aggregates. Porphyrinoid compounds, including chlorophylls, often form oligomers in solutions at the relatively high concentrations often used to measure weak spectral components. These oligomers typically exhibit CD associated with exciton coupling within the oligomers that is much stronger than monomeric (molecular) CD. The presence of the (BF)O(BF) group coordinated in the middle of the porphyrin would prevent p- stacking and hence inhibit

oligomerisation, the likely cause of the absence of the expected spectral signatures at the highest concentrations used.

In Supplementary Figure 11, the observed room temperature spectra for all isomers in 2-MeTHF are compared. The CD spectra in the Q-band region show distinctly different patterns for each fraction varying in the sign and relative amplitudes of the two Q-band component peaks. This distinction is used to assign structures to the isolates later in Supplementary Table 12. Supplementary Figure 11 also shows that the Soret-band region of the spectrum which also displays unique patterns for each fraction and hence could (in principle) facilitate assignment. However, using current computational techniques it is not possible to authoritatively predict these patterns.

Supplementary Figure 9. Comparative 298 K CD spectra De and ABS spectra eofFrl in CHCI3, hexane and 2-MeTHF obtained using various porphyrin concentrations in different solvents.

V / 1000 cm

Supplementary Figure 10. Comparative 298 K CD spectra De and ABS spectra e ofFr4 in CHCI3, hexane and 2-MeTHF obtained using various porphyrin concentrations in different solvents.

V / 1000 cnr ¹

Supplementary Figure 11. Comparative 298 K CD spectra De and ABS spectra s of Frl - Fr4 in 2-MeTHF obtained using various porphyrin concentrations (14-45 mM).

Low temperature spectra

Low -temperature ABS, CD, and magnetic circular dichroism (MCD) spectra were recorded using a quartz sample cell of approximate path-length of 1 mm. The cell was attached to a sample rod and lowered into an Oxford Instruments Spectromag SM4 cryostat cooled with liquid helium. Samples were cooled from room temperature to sub-77 K temperatures over a period of 2 - 3 min by controlled perfusion of helium vapour into the sample chamber. This procedure allowed a high quality strain-free optical glass ¹⁴ to be formed. The ABS, CD and MCD spectra were recorded simultaneously on a spectrometer ¹⁵ designed and constructed in the laboratory at the Research School of Chemistry (The Australian National University), and used a Hamamatsu R669 photomultiplier tube for detection. A field of 5 T was introduced for the MCD measurements. Samples were prepared as for the high -temperature measurements, using 2-MeTHF as the solvent, redistilled and filtered through dried neutral alumina. This solvent provided good quality low temperature glasses. Sample concentrations were in the range of 4-80 mM. Variations in cell path- length was corrected for by matching the absorption integration over the energy range of 14286 cm ¹ to 19608 cm ¹ to the same value in the (quantitative) 298 K data.

Supplementary Figure 12 shows the observed low-temperature ABS, CD, and MCD spectra. The CD signal is very weak and hence shows considerable noise under the experimental conditions, i.e. conditions optimised to minimise any possibility of oligomerisation and to provide high reliability ABS and MCD data. The primary purpose of these low -temperature measurements is to be able to separate the observed ABS spectra into its orthogonally polarised components. Two independent and orthogonally polarised electronic transitions, usually named Q _x and Q _y , are expected in the Q-band region, whilst the related bands B _x and B _y are expected in the Soret-band region. However, the Soret bands will mix with charge- transfer states arising from combinations of the porphyrinic N bands with transitions that move charge between the macrocycle ring and the fused quinoxaline group ¹⁶ .

Supplementary Figure 12. Comparison of relative ABS, MCD, and CD spectra taken in 2-MeTHF at 55-68 K in the Q-band (60-80 mM) (left) and Soret band (4-40 mM) (right) regions for Frl-Fr4. Analytical data inversion methods are used to convert the ABS and MCD raw spectra (black) into two orthogonal spectral components (red and blue) on the assumption of maximal intensity in the weaker band (the band coloured red). Concentrations used:

37 mM for Frl, 43 mM for Fr2, 27 mM for Fr3, and 28 mM for Fr4.; maximum ABS coeff. always < 1.2.

In MCD experiments, component states with one polarisation appear with +ve sign whilst those of the orthogonal polarisation appear with a -ve sign. When combined with ABS data, this observation allows the ABS to be deconvolved into two its x and y polarisation components. This was achieved not by band fitting as is the usual practice, but instead using an analytical data inversion scheme recently introduced ¹⁷ . In principle, such an analytical data inversion does not appear to be feasible, as it requires two more parameters to be deduced than there are actual experimentally quantities observed. However, we have shown that one equation of constraint is already known so that only one unspecified parameter remains. Further, we have shown that this remaining variable can be expressed in a bounded form to which deconvoluted band shapes are insensitive . Spectral components deduced using the minimum-allowable value for this unknown variable are shown in the figure, coloured red for the weaker component and blue for the stronger one. The assumption used attributes the maximum possible intensity to the red components, with alternate values for the arbitrary parameter serving to downplay the absorption strength of the red bands without significantly altering the shapes of the red and blue components. As a result, the band centres of the extracted components are reliably determined and may be compared to computational predictions. The deduced properties of the absorption bands are listed in Supplementary Table 7 whilst Supplementary Table 8 Supplementary Table gives the ratios of the MCD to ABS susceptibilities BID. The ratios of—B _y /B _x for each band are also given, these are unity for a 4-fold symmetric porphyrin.

For each sample, the Q-band origin region of 15400-16200 cm decomposes into an intense lower- frequency band (blue) and a weak high-frequency shoulder (red) shifted by 250 cm ¹ for Frl and Fr2 and by 220 cm ¹ for Fr3 and Fr4. The analytical inversion analysis does not allow for comparisons between molecules, however, and it is uncertain as to whether the intense band coloured blue for Frl and Fr2 corresponds to the band coloured blue for Fr3 and Fr4.

Supplementary Table 7. Deconvoluted properties of observed absorption spectral bands. ^a

Frl Fr2 Average

Band Pol.

S I X 15600 16382 0.125 15600 16371 0.129 15600 16377 0.127 52 y 15850 16467 0.05 15850 16470 0.048 15850 16469 0.049

S2-S1 250 85 250 99 250 92

53 x 21210 0.25 21210 0.25 21210 0.250

54 y 21600 21906 0.93 21600 21906 0.93 21600 21906 0.930

55 x 22320 0.51 22320 0.62 22320 0.565

56 x -23600 0.5 -23600 0.5 -23600 0.500

Band Pol. Fr3 Fr4 Average

51 x 15670 16445 0.11 15670 16450 0.111 15670 16448 0.111

52 y 15890 16539 0.057 15890 16535 0.056 15890 16537 0.057

S2-S1 220 94 220 85 220 90

53 x 21160 0.18 21160 0.19 21160 0.185

54 y 21550 22050 1.05 21550 21950 1.003 21550 22000 1.027

55 x 22370 0.38 22370 0.43 22370 0.405

56 x -23000 0.38 -23000 0.43 -23000 0.405 a: Polarisation directions x and y are arbitrary and not correlated between Q and Soret bands. VQO i ^s band origin, v the average absorption energy, and/the deconvolution-assumption-dependent oscillator strength.

. Fraction Q band Soret Band

BJD B _y /D _y -BJB., BJD _X BJD _y —BJB _X

Frl 0.0287 -0.0755 1.03 0.00277 -0.00358 1.05

Fr2 0.0245 -0.0680 1.02 0.00214 -0.00280 0.94

Fr3 0.0056 -0.0114 1.04 0.00075 -0.00052 0.95

Fr4 0.0056 -0.0117 1.04 0.00061 -0.00054 0.92

In the Soret-band region, the observed ABS spectra for all fractions are deconvolved into four spectral components: one intense component of one polarisation (coloured blue) and three components of the alternate polarisation (coloured red). As the analyses of the Soret and Q-band regions are essentially independent of each other, there is no proscribed relationship between the state polarisations coloured the same way for each band.

The available (noisy) low -temperature CD spectra are also shown in Supplementary Figure 3.

Comparison of relative ABS, MCD, and CD spectra taken in 2-MeTHF at 55-68 K in the Q-band (60-80 mM) (left) and Soret band (4-40 mM) (right) regions for Frl-Fr4. Analytical data inversion methods are used to convert the ABS and MCD raw spectra (black) into two orthogonal spectral components (red and blue) on the assumption of maximal intensity in the weaker band (the band coloured red). The peaks in the CD spectra correlate with the maxima of the deconvolved spectral components, indicating again that they relate to molecular features rather than to properties of aggregates. The qualitative shapes of the CD correspond to those observed at room temperatures (Supplementary Figures 9 to 11), indicating that these much-better-resolved features can be attributed to the peaks in the deconvolved low-temperature ABS/MCD spectra, for the purposes of spectral assignment.

S6. DFT Calculations

All geometry optimisations, vibrational frequency, NMR, electronic absorption and electronic circular dichroism calculations were carried out using Gaussian-09 18. All structures are characterised using vibrational frequency analyses.

a, DFT Geometries

Structural models for 2a and 3a were optimised at the B3LYP-D3/6-31G(d,p) level ^{19 21} , with diffuse functions on the boron, oxygen and fluorine atoms and the inner four porphyrin nitrogens added. In this method, empirical dispersion is included using Grimme’s original D3 damping function 21. Solvent effects were included using the polarisable continuum model ²² using the standard parameters for chloroform and the solute- solvent dispersion interaction ²³ included. Integrals were calculated using an “ultrafme” grid and tight convergence criteria for the SCF. Coordinates for b enantiomers were generated from the related a species by internal reflection.

b, OFT ffilr stc barriers to BAI In simple molecules

The calculated BAI barriers for some simple compounds made from combinations of first and second row elements are given in Supplementary Table 9. Processes like inversion of Si-O-Si bonds have very low barriers, with B O B bonds typically having a barrier that is far too low to facilitate isolable isomers at room temperature. In such cases, BAI can only be observed if the external environment compresses or tensions the bonds enough to create a sizeable barrier. Inversion of bonds involving S as the central atom can be very difficult, however, making isomers very stable and akamptisomerisation difficult to observe.

Supplementary Table 9. BAI inversion barriers in some simple compounds.

Bond Equilibrium D G / AG*/

Species

angle angle kJ mol ¹ kJ mol ^{1 b}

H-O-H 104.7° 127 132.51

C-O-C 112.5° 149 154.66

B-O-B 120.3° 38

Si-O-Si 137.9° 6

H-S-H 93.1° 284 289.67

C-S-C 99.5° 293 310.16

B-S-B 99.9° 116

Si-S-Si 101.1° 112

a: relative electronic energy of specie with bond angle = 180°, b: B3LYP-D3/6-311++G(2d,p) water solvation, c: B3LYP-D3/6-31+G(d) chloroform solvation, b: at the W2-F12 level of theory, from Lars Goerigk & Rahul Sharma The INV24 test set: how well do quantum-chemical methods describe inversion and racemization barriers? Can. J.

Chem. 2016 94:1133-1143

DPT Reaction Pathways, Transition States and Reaction Rates

I. OFT B-O-B Inversion (Aka p lso ertsat en) Transition State Energies

The BAI transition state linking 2a and 3a was optimised at the B3LYP-D3/6-3 lG(d) level. The transition state, called , is shown in detail in Supplementary Figure 13.

Supplementary Figure 13. Transition-state structures for various isomeric interconversions. Hydrogens omitted for clarity.

!L DFT E-Ό-1 Coupled Pair of Torsions Transit!®» State Energies

The linear nature of the B-O-B bond angle seen in the BAI transition states is a particular example of the more general case where the oxygen atom moves through the pseudoplane of the macrocycle and the B-O-B angle not necessarily linear. This is accomplished by the coupled rotation of bond torsions centred on each of the B-0 bonds (L—B— O-L)).

If we consider the simpler case of the higher symmetry system 6, then, due to symmetry considerations, any transition state structure that leads to BAI must meet the following geometric conditions;

1. meso carbons C-10 and C-20 and the oxygen atom must be collinear and lie on the C ₂ axis as shown in Supplementary Figure l4b,

2. the vector formed by joining C-5 and C-15 must intersect the C ₂ axis at right angles as shown in Supplementary Figure 14b, and

3. the oxygen atom is located at this point of intersection when and only when, the B-O-B bond is linear.

A scan of the potential energy surface at fixed B-O-B angles was carried out at the B3LYP-D3/6-3lG(d) level using the constraints above with frequency calculations used to determine the free energies and confirm the transition- state-like nature of structure, with the results plotted in Supplementary Figure l4a. The lowest energy transition state structure has a linear B-O-B angle and C _2h symmetry.

The older semi-empirical AM1 and PM3 methods each predict a double well potential showing little agreement between their key features. This reflects their poor treatment of B-0 bonds and unusual geometries. The newer and more sophisticated PM6 method closely reproduces the DFT single potential well as shown in Supplementary Figure l4c.

The relatively flat nature of the potential well for small deviations from linearity (a 20° deviation equating to 7 kJ mol ¹ ) reflects the fact that the normal vibrational mode corresponding to these transverse displacements (A" symmetry, 178.5 cm ¹ ) is of similar energy as that corresponding to the linear BAI mode (A' symmetry, 206.3 cm ¹ ), and hence both are expected to be similarly populated at ambient temperatures. Never-the-less, at the temperatures < 400 K we would not expect a deviation from linearity for the B-O-B angle of more than 25°. For interconversion between akamptisomers to proceed via a“bond rotation” mechanism analogous to that seen in some R ¹ R ² C=NR ³ type systems, the B-O-B angle would have to deviate from linearity by more than ~55° with the transition state energy increasing from ~l05 kJ mol l to at least 165 kJ mol ¹ as indicated in Supplementary Figure l4a Supplementary Table by the red and green vertical dashed lines.

Transition state B-O-B angle / Degrees

Supplementary Figure 14. a) Transition- state (TS) energies for 6 for BA1 arising through coupled torsion pairs with the central near-linear region detail shown inset. The left axis shows the TS energy relative to the ground state. The right axis shows the TS energy relative to that for the linear B O B transition state. The red dot-dashed vertical lines correspond to the B O B angles of 118° and 242° found in the ground state of 6. The green dashed vertical lines correspond to the less constrained B O B angles of 133° and 227° found in the ground state of 7. b) Plan and low-oblique views of a transition state structure. The oxygen and two meso carbons, C- 10 and C-20, lie on the Cf axis represented by the purple arrow. The second line joining meso carbons C-5 and C-15, intersects the C7 axis at right angles. Hydrogen atoms omitted for clarity c) Comparison of potential well as calculated by different methods. The older AMI and PM3 methods (dashed lines ) predict a double well indicative of a double torsional mechanism whereas the more accurate DFT (solid blue) and newer PM6 semi-empirical (solid red) methods predict a single well in good agreement. isi DFT ta-plasse (BF)O(BF) Rot.atfim (Strepstsomertsatfoo) Trao.sflioti State Eoe.rg.tes

Optimised geometries and free energies for solution phase structures of the mcwo-unsubstitutcd analogues of 2a, 2b, 3a, and 3b, as well as their interconnecting transition states obtained by rotating the (BF)O(BF) group inside the porphyrin macrocycle (strepsisomerisation, see Section 8.c for the formal definition), were calculated at the B3LYP-D3/6-3l+G(d) level with the diffuse functions necessary to accurately model the bond-breaking/making process. Solvent effects were included using the polarisable continuum model using the standard parameters for dichloromethane and the solute-solvent dispersion interaction included. For the 2,3 -porphyrin substitution pattern studied here, the resulting strepsisomerisation cycle gives rise to two rounds of akamptisomerisation (not by the BAI mechanism) and then enantiomerisation, interconverting all products 2a, 2b, 3a, and 3b. This is shown in Supplementary Figure 15, with results collected in Main Text Table 2. The strepsisomerisation process is illustrated in Supplementary Video 3, with the transition state TS _2a 3a connecting 2a and 3a also shown in Supplementary Figure 13.

Supplementary Figure 15. Concerted unimolecular isomerisation pathways affected through rotation of the (BF)O(BF) group in the plane of the macrocycle (strepsisomerisation). All isomers interconvert through successive 90° rotations with intervening transition structures indicated. Ar = 3, 5-di -tot-butyl phenyl for the real systems.

Calculated free energies for the Ar = H analogues are at the B3LYP-D3/6-31G+(d) level including implicit dichloromethane solvation. All indicated stereochemistry is relative to the porphyrin ligand. Atoms and bonds marked in red are above the pseudoplane of the porphyrin whilst those in blue are below it.

* The interconversion of akamptisomers is not through BAI nor is the interconversion of enantiomers through the dual inversion of the stereocenters; in each case these isomerisations are a feature specifically arising from the combined symmetries of both the ligand and the frare,sOk/-(BF)0(BF) group.

iv. OFT FMorkle Dissociation ami Cadonlc Species Transition State Energies

The free energies for fluoride ion dissociation from the meso-unsubstituted analogues of 2 - 4 under experimental conditions (conditions of synthesis or just simple solutions) were calculated at the B3LYP- D3/6-3l+G(d) level with the diffuse functions necessary to accurately model the anionic species. Solvent effects were included using the polarisable continuum model ²² using the standard parameters for dichloromethane and CHCI ₃ (representing CDCI ₃ ) and the solute-solvent dispersion interaction 23 included.

Whilst B-F bonds are particularly strong, dissociation in solution was predicted to be energetically accessible due to the highly delocalised nature of the resulting cationic porphyrin, with the nature of the resulting anion playing an equally critical role.

The special importance of these reactions arises from the ability of the cationic porphyrin to undergo akamptisomerisation processes analogous to those of the neutral species, but also to undergo a 1,3- fluoride shift from one boron to the other so as to facilitate enantiomerisation. Example transition structures for each of these are shown in Supplementary Figure 13. Supplementary Figure

Overall, the effect of these fluoride loss reactions is to enable a wide range of pathways interconverting all the isomers upon subsequent fluoride recombination. Interrelationships between 2a, 2b, 3a, 3b, 4a and 4b are sketched in Supplementary Figure 16, with key data collected in Main Text Table 2.

For the following reactions, the unionised starting compounds are generalised as“P-F” where“P” represents the isomers of B ₂ OFpqx. Reaction rates are calculated for the dissociation-promoted pseudo reaction:

where P ⁺ⁱ represents the six different transitions states named in colour in Supplementary Figure 16. Using the relationships for the activation of P ⁺ to a transition state

(values of AG _C shown in Supplementary Figure 16) is used to solve each concentration dependent reaction rate. As the Gaussian package calculates free energies with respect to a gaseous standard state, the molar volume being 22.4 L, whilst in solution the standard concentration is 1 M, a correction to AG" of RT In (22.4 L/l L) = 8.0 kj mol ¹ must be added. The method for different reactions is then:

Uncatalysed simple dissociation: P-F(solv) ^ P (solv) + F (solv)

The barriers are simply calculated as AG _prodUcts - AG _{rai lim} ^ + AG _C

HNEh ⁺ catalysed dissociation:

P F(solv) + H-NEt ₃ ⁺ ( _SO iv) P ⁺ (soiv) + F-H-NEt ₃ ( _SOiV )

As HNEt ₃ ⁺ is a by-product of synthesis then [HNEt ₃ ⁺ ] = 2[PF]. With [FHNEt ₃ ] = [P ⁺ ], the rate for this reaction becomes

K _F = [P ⁺ ] ² / 2[PF] ²

Combining this with (2) gives

KF = ([P ⁺ⁱ ]/ K _c ) ² / 2[PF] ²

and combining with (1) and simplifying gives

K = K _C (2 K _F = _e ^AGtlRT

so that

AG ¹ = AG _c + D G _F - ¼RT ln 2

BF - NEt catalysed dissociation:

P F(solv) + BF ₃ - NEt ₃ ( _SO iv) -A P ⁺ (sotv) + BF ₄ (solv) + NEt ₃ ( _SO iv)

With NEt ₃ modelled as NMe ₃ ,

e _~ AG _P /kT _ _K [Me ₃ N][BF ₄ ][P ⁺ ] [Me ₃ N] _{+ 2}

F [Me ₃ N-Bf¾][FP] [Me ₃ N-Bf¾][FP] ^L

From the reaction conditions, [Me^N-BF^ ]— 0.16 M and can be treated as a constant, [Me ₃ N] - 0.011 M as this was added in slight excess and is taken as a constant, [FP] = 0.0042 M is also taken as a constant (this assumes that only a small fraction of it is actually dissociated). Combining with (1) and (2) gives

Uncatalysed F ^~ S _N? reactions on 4a and 4b:

P-F(solv) F (solv) ^ [F-P-F] (solv) ^ Ao-P-F(solv) + F (solv)

The cisoid (BF)O(BF) motif present in 4a and 4b exposes the two boron atoms to the attack from the opposite face of the macrocycle to give 2a, 2b, 3a, and 3b. The reaction was modelled by optimising the stepwise approach and withdrawal of F and fitting an exponential function to the AG data points to estimate the energy of each P-F _(SOiV) + F _(SOiV) at infinite separation and the maximum energy of the bound complex [F-P-F] _(soiv) .

Uncatalysed F ^~ loss with counter-facial addition reactions on 4a and 4b:

This uncatalysed reaction converting 4a and 4b to 2a, 2b, 3a, and 3b provides an estimated upper limit for the barrier to this depletion mechanism. OFT Potential Energy Seriate scans

Optimised geometries and enthalpies for the gas-phase structures of the H/eso-un substituted analogues of 2a and 3a were calculated at the B3LYP-D3/6-3 lG(d) level under the constraint of fixed B-O-B bond angles ranging from 95 to 180° in 27 equal angle increments in order to generate the two halves of the potential energy surface along the B-O-B inversion reaction coordinate. A similar scan was performed for the interconversion of 4a and 5a. The produced surfaces are shown in the main text Figure 2. How the molecular structures evolve from 2a and 3a is show in Supplementary Video 2. b DFT Ή-f nd ⁵⁹ F MR spectra

NMR calculations using the optimised 2a and 3a geometries were carried out under the Gauge- Independent Atomic Orbital method ²⁴ using the B3LYP functional ¹⁹ with the 6-311++G(2d,p) basis set applied to all atoms of the extended macrocycle and the 6-3 l+G(d,p) basis set to all e.so-aryl atoms. Empirical dispersion was included using Grimme’s original D3 damping function ²¹ . Solvent effects were included using the polarisable continuum model with the standard parameters for chloroform and the solute-solvent dispersion interaction included. Isotropic chemical shifts for protons are reported relative to the calculated ¹ H shift of tetramethylsilane (TMS) and those for fluorine relative to the calculated ¹⁹ F shift of trifluorochloromethane (CF3CI). The TMS and CF ₃ Cl geometries were optimised at the B3LYP- D3/6-3l l++G(2d,p) level. Integrals were calculated using an“ultrafme” grid and tight convergence criteria for the SCF. The TMS and CF ₃ C1 NMR calculations were conducted at the same level of theory as for the porphyrins using identical settings. f, DFT Absorption and Circular Dichro!sm spectra

Electronic absorption and circular dichroism spectra were modelled using the optimised geometries for 2a and 2b only as their enantiomers give identical results except for the opposite sign of the calculated rotatory strengths. At least 8 electronic transitions were determined, the first two occurring in the Q-band region while the remainder are the Soret and nearby bands. Two different asymptotically corrected density functionals, CAM-B3EYP ²⁵ ’ ²⁶ and wB97XD ²⁷ were used as well as the configuration-interaction singles (CIS) method, and three different basis sets were used. The wB97XD results include corrections for intramolecular dispersion interactions, while for the largest basis set used, 6-31++G(2d,p), the D3 dispersion correction ²¹ was added to CAM-B3EYP calculations. Solvent corrections were also sometimes applied using the polarisable continuum model with the“noneq=read/write” commands to properly treat charge-transfer bands. The implicit solvent was set to either CHC1 ₃ or else to 2-MeTHF parametrised as THF with the dielectric constant changed to e = 6.97. Calculations were also performed both for the full molecule with tetra-nic.wG, 5-di-/ _{<? /} 7-butyl phenyl substituents and for simplified molecules without them.

Results are given in Supplementary Table 10 for 2a and Supplementary Table 11 for 3a, featuring calculated excitation energies, electric-dipole oscillator strengths, rotatory strengths, the angle between the transition electric dipole vector and the direction made by projecting the B-B vector onto the plane best representing the four pyrrolic rings, and the“E-M” angle between the electric dipole moment and the magnetic dipole moment. The most noticeable common feature is that the E-M angles are all near 90°. Rotatory strengths are proportional to the cosine of this angle and hence are expected to be small and to be dominated by subtle effects that manipulate the perceived angle. This result reflects the geometrical property that chirality in these molecules is a subtle effect arising through the interplay of the distortions and asymmetries introduced by the (BF)O(BF) group combined with the asymmetry introduced by mono quinoxalino ring fusion. Supplementary Table ectral properties of 2a.

CAM- CAM- CAM- method B3LYP B3LYP wB97XD wB97XD B3LYP wB97XD CIS basis 6-31G* 6-31+G 6-31G* 6-31+G* 6-31+G* 6-31+G* 6-31+G* solvent none none none none none none none

H

0®1 Energy / cm ¹ 16440 16250 16470 16120 16090 16930 16620 18370

Osc. Str. 0.059 0.057 0.062 0.078 0.058 0.035 0.029 0.080 Rot. Str. ^a 9 10 12 14 9 -9 -10 -40 TM angle ^h / 29 31 30 28 96 96 120 E-M angle ⁶ / 86 85 86 87 94 95 84

0®2 Energy / cm ¹ 16740 16570 16790 16480 16460 17490 17140 19880

Osc. Str. 0.009 0.011 0.012 0.024 0.009 0.009 0.010 0.085 Rot. Str. ^a 0 1 1 2 1 -5 -4 -11 TM angle ⁶ / ⁰ 7 6 13 10 63 109 57 E-M angle ⁶ / ⁰ 87 88 87 86 100 98 105

0®3 Energy / cm ¹ 24480 24110 24510 23380 24740 26100 26410 33050

1.050 1.064 1.059 1.654 1.129 0.410 1.298 2.874

27 39 47 255 106 1 225 114

86 93 83 73 97 35 16 86 85 83 70 90 29 92

0®4 Energy / cm ¹ 24700 24320 23450 24950 26280 26660 34110

1.255 1.314 1.635 1.241 1.399 0.707 0.886

-24 -20 -229 -99 110 -139 56

10 10 162 34 30 48 91 91 96 81 100 73

0®5 Energy / cm ¹ 26360 26270 26250 28540 28140 36310

Osc. Str. 0.641 0.530 0.675 0.041 0.033 1.833 Rot. Str. ^a 8 8 -6 -1 -6 -147 TM angle ⁶ / ⁰ 138 137 38 142 144 62 E-M angle ⁶ / ⁰ 88 87 93 94 102 91

0->6 Energy / cm ¹ 28450 28210 28000 28920 28690 37640

0.013 0.191 0.005 0.465 0.010 0.057

2 -13 3 -88 13 -17

53 41 37 119 150 96 82 93 73 98 55 135

0®7 Energy / cm ¹ 28710 29470 29260 29550 38340

Osc. Str. 0.043 0.112 0.025 0.339 0.125 Rot. Str. ^a 25 11 -6 -64 49 TM angle ⁶ / 145 135 47 61 57 E-M angle ⁶ / 47 88 92 98 94

0®8 Energy / cm ¹ 29280 30060 30670 31030 40050

Osc. Str. 0.004 0.036 0.058 0.017 0.109 Rot. Str. ^a 2 25 53 34 -8 TM angle ⁶ / ⁰ 140 139 35 50 79 E-M angle ⁶ / 77 65 73 78 122 a: in units of 10 ⁴⁽ ^ erg esu cm Gauss ¹ b: angle between electronic transition moment and the projection of the B-B vector onto the macrocyclic plane c: angle between the electric dipole and magnetic dipole transition moments d: dtp = 3,5-di-½ri-butylphenyl. Supplementary Table ectral properties of 3a.

CAM- CAM- CAM- method B3LYP B3LYP wB97XD wB97XD B3LYP wB97XD CIS basis 6-31G* 6-31+G 6-31G* 6-31+G* 6-31+G* 6-31+G* 6-31+G* solvent none none none none none none none

H

0®1 Energy / cm ¹ 16880 16690 16560 16620 17150 16900 18530

Osc. Str. 0.006 0.008 0.017 0.005 0.042 0.039 0.113 Rot. Str. ^a 9 10 14 9 14 13 -7 TM angle ^h / 83 95 82 51 51 49 E-M angle ⁶ / 85 84 85 87 87 89

0®2 Energy / cm ¹ 17180 17030 16960 17040 18120 17960 22620

Osc. Str. 0.064 0.063 0.098 0.065 0.001 0.001 0.050 Rot. Str. ^a -6 -7 -13 -6 1 1 -3 TM angle ⁶ / ⁰ 24 25 25 27 45 45 E-M angle ⁶ / ⁰ 99 101 100 77 71 48

0®3 Energy / cm ¹ 24620 24240 23530 24870 26130 26350 32970

1.143 1.164 1.701 1.226 1.147 1.252 3.032

-32 -34 -129 -60 -116 -141 -165

76 74 107 13 14 19 98 98 105 105 107 117

0®4 Energy / cm ¹ 25240 24840 24040 25600 26660 27270 35430

1.413 1.392 1.727 1.505 0.609 0.775 0.982

58 52 122 94 13 59 -26

9 9 169 106 99 88 85 85 83 88 85 70

0®5 Energy / cm ¹ 26720 26700 26580 28960 28690 38100

Osc. Str. 0.266 0.238 0.259 0.132 0.009 0.007 Rot. Str. ^a -54 -61 -56 72 7 153 TM angle ⁶ / ⁰ 125 124 52 92 46 86 E-M angle ⁶ / ⁰ 105 109 107 75 60 62

0®6 Energy / cm ¹ 28480 28260 28240 29100 28780 37640

0.044 0.199 0.001 0.009 0.004 0.057

25 29 1 20 23 -1 14 12 121 35 97 104 79 84 76 29 5 88

0®7 Energy / cm ¹ 29350 29650 29800 38760

Osc. Str. 0.047 0.288 0.066 0.050 Rot. Str. ^a 11 -54 -4 2 TM angle ⁶ / 150 102 86 126 E-M angle ⁶ / 89 99 94 79

0®8 Energy / cm ¹ 29890 30260 30630 38900

Osc. Str. 0.065 0.096 0.219 0.326 Rot. Str. ^a -40 -11 -39 -93 TM angle ⁶ / ⁰ 139 154 114 113 E-M angle ⁶ / 110 96 127 92 a: in units of 10 ⁴⁰ erg esu cm Gauss ¹ b: angle between electronic transition moment and the projection of the B-B vector onto the macrocyclic plane c: angle between the electric dipole and magnetic dipole transition moments d: dtp = 3,5-di-½ri-butylphenyl. S7. Isomer Structure Assignments

Unfortunately, X-ray crystallographic and vibrational CD investigations proved problematic, and hence assignment of the four observed fractions Frl, Fr2, Fr3 and Fr4 to the four expected products 2a, 2b, 3a, and 3b is performed by comparison of the results of NMR, UV-Vis absorption, CD, and MCD

spectroscopies with those predicted using DFT, also utilising the observed and calculated thermal isomerisation pathway. A summary of the results is presented in Supplementary Table 12. Frl is assigned to 2b, Fr2 to 2a, Fr3 to 3a, and Fr4 to 3b.

Supplementary Table 12. Assignment of structures to HPLC fractions by comparison of measured and calculated ¹ H and ¹⁹ F NMR, observed thermal isomerisation processes, and CD Spectra.

Thermal isomerisation Q-band intense peak~15600 cm ^'1 Soret shoulder at -22500

Fraction NMR ciiT^ possibility 1 possibility 2 CD sign CD strength Ass. CD sign CD strength Ass.

Frl 2 a b s 2b + w 2b?

Fr2 2 b a + s 2a w 2a?

Fr3 3 b a - w 3a s 3a

Fr4 3 a b + w 3b + s 3b

Isomer Assignments; NM

Due to the conformational landscapes and complex nature of the induced magnetic environments inherent in the EFOF -pqx systems, DFT calculations of isotropic chemical shifts were of utility in the

interpretation of experimental isotropic chemical shifts with the view of assigning structures to the isolated fractions Frl - Fr4.

We focussed on the b-pyrrolic H and aromatic C centres that chemical intuition, supported by the DFT NMR calculations, were predicted to be strongly structurally diagnostic (since enantiomers show the same NMR spectra and this method is not able to discriminate between a and b, but quite different spectra are predicted for 2 - 5). The DFT-calculated isotropic b-pyrrolic ¹ H, ¹⁹ F and ¹³ C chemical shifts for 2 and 3 corresponding to all experimentally assigned aromatic peaks of (Frl + Fr2) and (Frl + Fr2) are listed in Supplementary Table 13 and shown correlated with in Supplementary Figure 17. Good agreement is found only when Frl and Fr2 are assigned to racemate 2 and Fr3 and Fr4 are assigned to racemate 3. This NMR result, combined with the observed thermal isomerisation process, means that of the 24 different ways in which Frl, Fr2, Fr3 and Fr4 could be assigned to the molecules 2a, 2b, 3a, and 3b, only four possibilities remain feasible. Identification of any single fraction is then sufficient to determine the identity of all other fractions.

Supplementary Table 13. DFT calculated b-pyrrolic ¹ H. ¹⁹ F and ¹³ C isotropic chemical shifts corresponding to all experimentally assigned aromatic peaks for racemates 2 and 3.

Racemate 2 (as 2a) Racemate 3 (as 3a)

Position ³ H d / ppm Position ' H 6 / ppm

H7 9.12 H7 9.61

H8 9.06 H8 9.68

H12 9.06 H12 8.70

H13 9.54 H13 8.89

H17 9.82 H17 8.89

H18 10.03 H18 9.29

Position ¹⁹ F d / ppm Position ¹⁹ F d / ppm

F ^a -175.0 F ^a -177.1

F ^p -203.9 _F P -202.4

Position ¹³ C d / ppm Position ¹³ C d / ppm

C5 134.43 C5 124.01 C6 154.84 C6 149.89

C7 127.04 C7 130.24

C8 142.43 C8 146.06

C9 154.97 C9 146.97

CIO 135.26 CIO 137.08

Cl l 133.25 Cl l 155.17

C12 146.00 C12 141.49

C13 133.25 C13 129.12

C14 147.69 C14 156.30

C15 129.63 C15 139.65

C16 145.53 C16 151.65

C17 131.94 C17 129.47

C18 144.82 C18 139.93

C19 152.33 C19 159.59

C20 129.95 C20 129.46

C26 138.29 C26 138.50

C27 135.53 C27 135.63

C28 136.01 C28 135.78

C29 137.48 C29 137.17

C25a 148.38 C25a 147.73

C29a 148.98 C29a 148.73 p-Ar5 109.00 p-Ar5 109.29 p-ArlO 110.50 p-ArlO 106.39 p-Arl5 108.64 p-Arl5 109.20 p-Ar20 105.22 p-Ar20 110.18 o-Ar5 118.05 o-Ar5 122.00 o-Ar5 119.68 o-Ar5 123.27 o-ArlO 126.64 o-ArlO 120.84 o-ArlO 127.92 o-ArlO 121.22 o-Arl5 117.92 o-Arl5 118.55 o-Arl5 122.55 o-Arl5 121.19 o-Ar20 125.29 o-Ar20 120.22 o-Ar20 128.38 o-Ar20 123.09

¹ H ~ p-pyrro!ics ¹ H - 0-pyrrofics

³ C - Extended macrocycle C - Extended macroeycle

Supplementary Figure 17. Comparison of experimental and DFT calculated b- pyrrolic ¹ H, ¹⁹ F and aromatic ¹³ C NMR isotropic chemical shifts, based on the possible alternative assignments of: Left- Frl and Fr2 to racemate 2, and Right- Frl and Fr2 to racemate 3. Red- data for molecules 2a and 2b, blue- data for molecules 3a and 3b; tie lines in (a) indicate vicinal /hpyrrolic proton pairs, (c) adjacent /7-pyrrolic carbons and (d) the para- and two ortho carbons of individual meso-aryl groups. b. Isomer Assignments, ABS,€0, and CD

It is relatively straightforward to interpret the calculated spectra in Supplementary Tables 10

Supplementary Table and 11 for the two Q-bands in terms the observed spectra in Supplementary Figures 9 to 12 Supplementary Figure . Invariably a medium- strength Q-band is predicted with a polarisation direction aligned in the B-O-B plane along with a weak to very weak Q-band. The weak band has a somewhat unpredictable electronic polarisation, arising from subtle mixing of weak absorption effects. The prediction of a strong component and a weak component is in agreement with the experimental observations. The intensity of the strong component is not greatly different for 2a and 3a, also in agreement with observation. A feature of the calculations in poor agreement with observation, is the splitting between the two Q bands (the difference between the weak band and the strong band), which is observed to be 220-250 cm ¹ but calculated by the DFT methods to be ca. 500 cm ¹ for 2a and 1000 cm ¹ for 3a for porphyrins without meso substituents and to be ca. 350 cm ¹ for 2a and -350 cm ¹ for 3a for the full molecules. Such errors are expected, however, as random errors of ca. 1000 cm ¹ are generally found when these DFT methods are applied to predict the Q-band splitting in porphyrin and chlorophylls ’ . However, these same methods usually predict the electric -dipole oscillator strengths and transition moment directions to useful accuracy , and the relative insensitivity of these properties to calculation method indicates the robustness of the stereochemistry assignments made from this data in

Supplementary Table 12.

The calculated spectra in the Soret-band region for molecules without meso substituents also closely parallel the observed spectra. A Soret component of one polarisation is predicted to give rise to the most intense peak whilst the Soret band of orthogonal polarisation is split into two components at lower and higher frequency, as is observed. Examination of the wavefunctions involved in the excitations indicates that it is a porphyrin to quinoxaline charge-transfer band that interacts with the Soret band to produce this effect. However, the magnitudes of the rotatory strengths are not predicted robustly enough to allow for assignment of the akamptisomers but they do allow the R and S stereochemistry to be determined, producing an assignment in agreement with the others presented in Supplementary Table 12. However, the analogous results obtained including the 3.5 - d i - c rt - b ut y 1 p h c n y I substituents see the charge-transfer band moving to high energies and the two Soret bands presenting as single peaks. This result is inconsistent with the experimental observations. Hence the predictions made using calculations of the unsubstituted molecules are unreliable and are not used in assigning the chiral structures. It would seem that the calculations are not capable of dealing with the meso substituents, the inversion in energy of the predicted Q-bands noted earlier being another consequence.

A summary of the data presented in Supplementary Table 12 is that all spectral interpretations suggest the same assignment, this being one of the four assignments consistent with the unambiguous NMR and kinetics data from out of a set of 24 possible assignments. This evidence is sufficient to assign the chemical identity of each resolved reaction product.

S8. Nomenclature

a. Fallings and weaknesses of existing nomenclature

The unusual nature, recent discovery, and (currently small) number of examples of compounds in this class has highlighted weaknesses and indeed failings of existing nomenclature. The nomenclature used in Chemical Abstracts (CAS) listings is ambiguous as it does not fully address the stereochemistry of these compounds. For example, the (BF)O(BF) porphyrins are currently listed in CAS using additive systematic IUPAC nomenclature, i.e., for the compound with CAS Registry Number 1022915-61-2, the name is difluoro-p-oxo[p-[tctraphcnyl-21 f/,23//-porphinato(2- )-KA ^{,2 l} ,K/V ²² :KA ^/2 \K/V ²⁴ JJdi boron. In a similar fashion, the (BF)O(BF) corrole complex CAS Registry Number 1013965-93-9 is named [m-[ 1 ,2,3, 7,8,12,13,17,18,19-decadehydro-21,22-dihydro-5,10,15-triphen ylcorrinato(3-)-K/V ²¹ ,KiV ²⁴ :K/V ²² ,K/V ²³ ]] difluoro-p-oxodiborate(l-). However, the first is a transoid compound and the second a cisoid compound, and the alternate forms of each are, in principle, feasible and would be assigned the same name: CAS

C

The most obvious difference between the two ligation modes demonstrated are the positions of the boron atoms relative to the macrocycle. There does exist a system of a/b stereodescriptors for defining the different faces of a macrocycle ³¹ which could, in principle, be used to indicate the single protmding BF in the transoid case, or the two co-facially protruding BF groups in the cisoid case. This usage, however, is somewhat lacking in that it introduces a new source of ambiguity in the case of porphyrinoid macrocycles as“/ is frequently used in a non-systematic way to indicate the //-pyrrolic positions.

Porphyrin complexes featuring the unsymmetrical bridge group B(OH)OB(Ph) prepared by Belcher el al . demonstrate another shortcoming of existing nomenclature. Under the assumption of the bridge group adopting a transoid configuration, there is the question as to which of the now distinct borons occupies the position that is in-plane to the macrocycle. This is demonstrated below for CAS Registry Number 1022915-75-8, which has been assigned the name hydroxy-p-oxophenyl[p-[5, 10, 15,20- tetrakis(4-methylphenyl)-21//,23//-porphinato(2-)-K/V ²¹ ,KiV ² : K/V ² \K/V ²⁴ J J di boro

Ar = 4-methylphenyl Ar = 4-methylphenyl Ar = 4-methylphenyl

CAS number: 1022915-75-8 ( parvo,amplo ) ( amplo,parvo )

The low-symmetry (BF)O(BF) porphyrin isomers studied in this work further exemplify the shortcomings of existing nomenclature, especially when discussing the phenomenon of akamptisomerism. An ideal amendment to the systematic nomenclature would not only be to provide clear and concise unambiguous names but also make the relationships between stereoisomers clear and preferably obvious.

Is. Akamptisomers and autoakamptlsomer

Akamptisomers are isolable pairs of bond angle inversion (BAI) stereoisomers. As the bond angle inversion process does not involve bond breaking or making, all other absolute stereo-configuration assignments such as (R/S) remain unchanged. In order for the BAI mechanism to operate without being masked by the more familiar bond-torsional processes, the inverting group must be constrained by its local chemical environment by, for example, being embedded within a macrocycle or polymeric matrix. Whilst barriers to inversion can vary widely (see Supplementary Table 9), in an analogous way to atropisomerism, practical isolability at near ambient conditions demands that the barrier be > 90 kJ mol ¹ . An autoakamptisomer is where the product of BAI is indistinguishable from the starting species, i.e. a “degenerate rearrangement”.

Akamptisomerisation is the thermally activated process or interconversion between akamptisomers, for example, 2a ^ 3a and 4a ^ 5a.

c Strepsisomerlsatloo and the strepsisomerisation cycle

Strepsisomerisation refers specifically to the in-plane rotation of the whole binucleating bridge group about the axis normal to the pseudoplane of the macrocycle and centred on the ligand cavity. As it applies to a transoid (BF)O(BF) porphyrins, each successive 90° rotation potentially gives rise to a new isomer, depending upon the porphyrin-ligand’s symmetry. For porphyrins, a strepsisomerisation cycle constitutes the four isomers resulting from each successive rotation. Whilst the energetic barriers involved may make the actual experimental demonstration of this mechanism difficult (see e.g.

Supplementary Figure 15), it does provide powerful conceptual utility in the study of ligation isomerism for these systems.

ii parvo / amplo stereodescriptors, determination and meaning

In order to define stereodescriptors for BAI isomers that can be applied in the most general of cases, five points within the plane of inversion must be defined; the three centres M _I ^~ X-M ₂ that constitute the bond angle undergoing inversion, and two additional points Ei and E ₂ that represent the anchoring of Mi and M ₂ , respectively, to their constraining environment. Each E, is calculated by taking the mean of all extensively connected atomic centres bonded to M, and projecting this onto the plane of inversion. In the case of (BF)O(BF) porphyrins, these are each of the two nitrogens bonded to each boron, and their mean positions are highlighted in Main Text Figure 3. The fluorines are not“extensively connected”, i.e. they are not part of the anchoring environment, and are thus omitted in the definitions of E;. From these points, two angles are calculated 0 _! = M _l- E _l- E ₂ and 0 ₂ = M _2- E ₂ -E _I .

These angles are calculated for the stmcture to be named (0i and 0 ₂ ) and its corresponding reference BAI isomer (qί and 0 ₂ ). Subsequently, if

0, / 0' < 2/3: M, is assigned the stereodescriptor parvo (from Latin meaning“small”),

2/3 < 0, / 0 < 3/2: no stereodescriptor applies,

0, / 0 > 3/2: M, is assigned the stereodescriptor amplo (from Latin meaning“large”).

parvo: Latin; ablative, neuter, singular of parvus, meaning“small”.

amplo: Latin; ablative, neuter, singular of amplus, meaning“large, spacious”.

Whilst this numerical criterion is arbitrary, testing against all known B-O-B complexed macrocycles proved it to be robust even against the more challenging cases of cisoid (BF)O(BF) corroles.

These terms should always be italicised and placed in parentheses with any other stereodescriptors. If the ligated centre is chiral then the (parvolamplo ) stereodescriptor appears as an italic right subscript“p” or “a” to the R/Sl other stereodescriptor. If there is a choice regarding the numbering, then the parvo position is given priority for naming. One, both or neither ligated centres may be assigned a (parvolamplo) stereodescriptor.

In the case where a macrocycle ligates the bridging group and both stereodescriptors are assigned amplo then the oc/b prefix convention can be applied as for example, ( -amplo, -amplo ) or (b-//„. -A,).

The BAI process has the effect of interchanging any and all (parvolamplo) stereodescriptors, thus facilitating the easy recognition of akamptisomers, for example, (//,„//., )-B ₂ OF ₂ pqx and (A _; „// ,)-B ₂ OF ₂ pqx only differ by their (parvolamplo) assignments and are thus akamptisomers.

Also in the case where a macrocycle ligates the bridging group, parvo generally corresponds to the ligated centre being effectively co-planar (“piano ") with its ligated half of the macrocycle, with amplo centres being distinctly out-of-plane (“a piano”) with their ligated half of the macrocycle, thus the mnemonic; parvo « piano and amplo « aplano can provide a more structure-intuitive guide.

The situation in which the Mc-C-M ₂ angle is nearly linear is worthy of note. In this case, optimisation of the structure produced by BAI inversion usually results in a return to the original structure, making both 0, / 0,'= 1 and so no stereodescriptor is assigned. This result is both general and intuitive. Akamptisomerisation transition states, being midway between ground state structures, are thus autoakamptisomers .

In the unusual cases of the 1, 3-fluoride shift enantiomerisation transition states, both the fluorine and the oxygen atoms occupy positions on opposite sides of the macrocycle and each is bicoordinate with a bent geometry. Whilst it is physically impossible for both the B— O— B and B— F-B bond angles to invert, this simultaneous-dual inversion process can occur, at least conceptually. The outcome is that TS^ ⁺ and TS ⁺ constitute a pair of akamptisomers. The dual BAI in this case also interchanges the ( R ) and (S) stereodescriptors; something not seen in the single BAI cases.

e. No enclature for transitio structures

With the increasing ability to accurately model transition structures for chemical reactions, a natural consequence is the increasing need to unambiguously name such structures. In this work we introduce a system for doing so by simply adding the double dagger (£) symbol to the end of a name constructed using normal systematic nomenclature with careful attention to any stmctural idiosyncrasies not found in ground state geometries. For example, the B-O-B BAI transition stmctures we encounter here are characterised by a linear or near-linear bicoordinate oxygen, hence necessitating the use of the ( -2) symbol (See IR-9.3.2.1 ³³ ).

For abbreviated names, the double dagger symbol can be used as is or superscripted as desired.

i, Listing of all species and proposed systematic names

In Supplementary Table 14, names are given to all neutral molecules and anionic corroles considered in this work, accompanied by its numerical designation from the Main Text when available, its abbreviated name, and a proposed full systematic substitutive IUPAC name modified with our introduced parvo and ample stereodescriptors. Additionally, an alternative systematic additive IUPAC name is shown in blue for some species. For all structures, all indicated stereochemistry is relative to the porphyrin ligand with atoms and bonds marked in red being above the pseudoplane of the porphyrin whilst those in blue are below it. Supplementary Table 15 provides the same information for all defluorinated cationic species considered. The geometric angles leading to the specified values of the parvo and amplo

stereodescriptors in both tables are listed in Supplementary Table 16.

Supplementary Table 14. Names for all neutral porphyrins and anionic corroles considered. References listed as, for example IR-9.3.2.1, refer to specific sections in the“IUPAC Red Book” ³³ .

Structure Names

Supplementary Table 15. Names for all defluorinated cations considered. References listed as, for example IR-9.3.2.1, refer to specific sections in the“IUPAC Red Book” ³³ .

a: alternate ring numbering giving priority to parvo leads to TS3 _b 2 _b being named ( 1 /^Aom / j-B OF pqx and not ( 1 amplo , 34 - B ₂ 0 F ₂ pq x , b: BAI of a F transfer transition states requires the conceptual BAI of both the F and O atoms.

Supplementary References

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2 Muller, P. Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994). Pure Appl. Chem. 66, 1077-1184 (1994).

3 Moss, G. P. Basic terminology of stereochemistry. Pure Appl. Chem. 68, 2193-2222 (1996).

4 Muetterties, E. L. Topological representation of stereoisomerism. I. Polytopal rearrangements. J.

Am. Chem. Soc. 91, 1636-1643 (1969).

5 Muetterties, E. L. & Storr, A. T. Topological analysis of polytopal rearrangements. Sufficient conditions for closure. J. Am. Chem. Soc. 91, 3098-3099 (1969).

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