This application claims priority to Australian Provisional Application No. 2019903735 entitled “Dyes and Methods of Use” filed 4 October 2019, the contents of which are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

[0001] The present invention relates to novel red organic dye compounds suitable for use as laser dyes.

BACKGROUND OF THE INVENTION

[0002] Organic semiconductors based optoelectronic devices such as organic light-emitting diodes (OLEDs), organic field-effects transistors (OFETs) and organic photovoltaics (OPVs) have shown considerable advancement in areas of full colour displays, lighting, and energy conversion over the last few decades.

[0003] Use of organic semiconductors as the active gain medium for light amplification in organic solid-state lasers (OSSLs) is also of increased interest in the fields of organic optoelectronics. Apart from providing coherent light emission, OSSLs offer several other advantageous features such as wavelength tunability, mechanical flexibility and low cost with easy solution processing techniques when compared to inorganic counterparts. As a result, OSSLs have potential as a new light source for applications such as spectroscopy, chemical/bio-sensing and optical data communications .

[0004] With recent advances in OSSLs development, many organic semiconductor lasers have been demonstrated to exhibit extremely low amplified spontaneous emission (ASE) thresholds (£*) and high optical gains. This includes families of bis-styrylbenzenes, oligofluorenes and spiro derivatives with neat-film ASE thresholds as low as 0.6, 0.43 and 0.09 pJ cm ² for BSB-Cz, spiro-SBCz and octafluorene, respectively. Furthermore, Sandanayaka el al. (Appl. Phys. Express. 2019, 12, 061010) recently showed evidence of lasing action under current injection with BSB-Cz.

[0005] However, the emission colour of most of these materials essentially lies in the high energy range of the visible spectrum and only scarce materials have been found to exhibit low ASE thresholds in the red region (625-740 nm). For example, 4- di(4'-/£7 -butylbiphcnyl-4-yl)amino-4'-dicyano vinyl benzene was reported to exhibit the lowest neat- film threshold of 22 pj cm ² with an emission peak at ~650 nm (H. Rabbani- Haghighi et al., Appl. Phys. Lett. 2009, 95, 033305). Red and other longer wavelength laser dyes are of great interest with respect to numerous applications such as optical amplifiers for polymethylmethacrylate (PMMA) based polymer optical fibres (POFs) for short haul data transfer and metal-organic plasmonic devices.

[0006] Dye chromophores for longer wavelength applications typically require extended p-conjugation. This can results in strong p-p stacking in the solid state and can result in low photoluminescence quantum yields (PLQYs) due to aggregate induced luminescence quenching. Use of a host where the host absorbs high pump energy and then transfers to the guest may assist in addressing this problem.

[0007] Commonly used organic semiconducting hosts are usually wide bandgap semiconductor materials that require an ultraviolet light source for the excitation. This adversely leads to photo -degradation of the laser dyes and also limits the choice of pump source for these OSSLs. An inert polymer matrix such as polystyrene (PS) or poly(methyl methacrylate) (PMMA) that enables dispersion of the dye at low doping concentration is useful to overcome the issues of concentration quenching and photo degradation. However, this approach is not practical for charge injection and charge transport because PMMA is not a semiconductor, and restricts in optoelectronic devices.

[0008] Another reason leading to the rarity of high performance red organic laser dyes, especially in the deep-red region, is their high non-radiative decay rates due to the "energy gap law" (see, J. V. Caspar, T. J. Meyer, J. Phys. Chem. 1983, 87, 952), competing with their radiative decay rates (k _r ). It is noted that ASE thresholds are inversely proportional to the Einstein’s coefficient B, which itself is directly related to radiative decay rate by the equation:

B oc (c/8Tihv ³ ) k _r where c and v are the speed and frequency of light respectively, and h is Planck’ s constant. This means that low radiative decay rates of organic red emitting semiconductors consequently result in high ASE thresholds and in many cases, no ASE at all.

[0009] Indigo is one of the oldest natural dyes and has been produced worldwide on an industrial scale. Indigo derivatives are known for their excellent air stability, strong electron accepting capability and ambipolar charge carrier property in thermally evaporated films. Due to these attractive properties, indigo and its derivatives have received considerable attention as electroactive semiconducting materials for OFETs, OPVs and organic photodetectors (OPDs). However, energy loss due to single/double proton transfer as well as rotation around the central carbon-carbon bond of indigo leads to poor PLQYs, thus limiting their light-emitting applications.

[0010] A bay-annulated indigo derivative known as "Cibalackrot", on the other hand, has a highly rigid chemical structure, where the trans-cis isomerisation and proton transfer routes are prohibited due to the annulation of the amine and carbonyl groups to give strong covalent bonds. Hence, Cibalackrot derivatives, including polymeric derivatives, show strong luminescence with high PLQYs in diluted solution, and ambipolar charge transport in solid state. However, simple Cibalackrots have poor solubility in common organic solvents due to strong intermolecular interaction (e.g. P-P stacking). Moreover, Cibalackrot polymers require tedious chemical synthesis and also have poor batch to batch reproduction in molecular weight and polydispersity, obstructing their investigation in solid-state laser applications.

[0011] There is a need for improved red dyes for solid-state laser applications.

SUMMARY OF THE INVENTION

[0012] The present inventors have discovered novel red organic dyes that address one or more of the disadvantages of known dyes. Furthermore, the inventors have discovered advantageous dye:host combinations for use in solid state laser applications.

[0013] Accordingly, in a first aspect there is provided a dye compound of Formula (I):

Formula (I) wherein: aryl or heteroaryl;

R ¹ may be the same or different and is independently selected from the group consisting of optionally substituted alkyl, optionally substituted alkoxy, optionally substituted alkylenearyl, halogen and a group having the structure: integer from 1 to 5;

R ² may be the same or different and is independently selected from the group consisting of halogen and optionally substituted aryl; x is an integer from 1 to 3; and y is an integer from 0 to 4; or Formula (II), which are dimers of the compounds of Formula (I) connected by a linker:

Formula (II) wherein:

L is a linker group and , R ¹ , R ² , x and y are defined as above.

[0014] In some embodiments, is phenyl, furanyl, thiophenyl, pyrrolyl, carbazolyl, pyridyl or imidazolyl. In some embodiments, is phenyl or furanyl.

[0015] In one embodiment, the moieties of a compound of Formula (I) or Formula (II) are each phenyl and the compound is a compound of Formula (G):

Formula (G) wherein:

R ¹ may be the same or different and is independently selected from the group consisting of optionally substituted alkyl, optionally substituted alkoxy, optionally substituted alkylenearyl, halogen and a group having the structure: integer from 1 to 5; R ² may be the same or different and is independently selected from the group consisting of halogen and optionally substituted aryl; x is an integer from 1 to 3; and y is an integer from 0 to 4; or the compound of Formula (II) is a compound of Formula (IF), which are dimers of the compounds of Formula (G) connected by a linker:

Formula (IG) wherein:

L is a linker group and R ¹ , R ² , x and y are defined as above.

[0016] In some embodiments, the compound of Formula (I) is a compound of Formula (la):

Formula (la) wherein , R ¹ and x are as defined above for a compound of Formula (I). In some embodiments, is phenyl.

[0017] In some embodiments, the compound of Formula (I) is:

7,14-bis(4-dodecylphenyl)diindolo[3,2,l-de:3',2',l'-ij][l ,5]naphthyridine-6,13- dione, Cibalackrot A; 7, 14-bis(4-((2-ethylhexyl)oxy)phenyl)diindolo[3,2, 1 -de:3',2', G- ijj[ 1 ,5Jnaphthyridinc-6, 13-dionc, Cibalackrot B; or

7-(furan-2-yl)-14-(4-((2-octyldodecyl)oxy)phenyl)diindolo [3,2,l-de:3',2',r- ijj[ 1 ,5Jnaphthyridinc-6, 13-dionc, Cibalackrot I.

[0018] In some embodiments, the compound has the Formula (Ila):

[0019] In some embodiments, the compound of Formula (II) is:

14,14'-((9,9-dihexyl-9H-fluorene-2,7-diyl)bis(4,l-phenyle ne))bis(7-(4-((2- ethylhexyl)oxy)phenyl)diindolo[3 ,2, 1 -de:3',2', 1 '-ij] [ 1 ,5]naphthyridine-6, 13- dione), Cibalackrot- Fluorene Dimer C;

14,14'-([l,r:3',l"-terphenyl]-4,4"-diyl)bis(7-(4-((2- ethylhexyl)oxy)phenyl)diindolo[3,2,l-de:3',2',l'-ij][l,5]nap hthyridine-6,13- dione), Cibalackrot-m-phenyl Dimer D;

14,14'-((9,9-dihexyl-9H-fluorene-2,7-diyl)bis(4,l-phenyle ne))bis(7-(4-(2- octyldodecyl)oxy)phenyl)diindolo[3,2,l-de:3',2',r-ij][l,5]na phthyridine-6,13- dione), Cibalackrot Dimer E;

14,14'-([l,r:3',l"-terphenyl]-4,4"-diyl)bis(7-(4-(2- octyldodecyl)oxy)phenyl)diindolo[3,2,l-de:3',2',r-ij][l,5]na phthyridine-6,13- dione), Cibalackrot Dimer F; 14,14'-([1,G:4',1 "-terphenyl] -4,4"-diyl)bis(7-(4-(2- octyldodecyl)oxy)phenyl)diindolo[3,2,l-de:3',2',r-ij][l,5]na phthyridine-6,13- dione), Cibalackrot Dimer G;

14,14'-((9,9,9',9',9",9"-hexahexyl-9H,9'H,9"H-[2,2':7',2" -terfluorene]-7,7"- diyl)bis(4, 1 -phenylene))bis(7 -(4-(2-octyldodecyl)oxy)phenyl)diindolo[3 ,2,1- de:3',2',r-ij][l,5]naphthyridine-6,13-dione), Cibalackrot Dimer H; or

14,14'-((9,9-dihexyl-9H-fluorene-2,7-diyl)bis(furan-5,2-d iyl))bis(7-(4-((2- octyldodecyl)oxy)phenyl)diindolo[3,2,l-de:3',2',r-ij][l,5]na phthyridine-6,13- dione), Cibalackrot Dimer J.

[0020] In another aspect, there is provided a composition comprising a dye compound of Formula (I) or Formula (II) and a host matrix. In some embodiments, the host matrix comprises, consists of, or consists essentially of one or more excited-state intramolecular transfer (ESIPT) host materials. In some embodiments, the host matrix comprises one or more host compounds selected from l,3-bis(/V-carbazolyl)benzene (mCP), 4,· 4'-bis(/V-carbazolyl)- 1,1 '-biphenyl (CBP), 2-hydroxyphenylbenzothiazole (HBT), benzo[d]thiazol-2-yl)-5-(97/-carbazol-9-yl)phenol (HBT-Cz), flavone, benzotriazole, poly(9-vinylcarbazole) (PVK) or 2-( l -(aryl)- 1 //-phcnanthro[9, 10- d]imidazol-2-yl)phenol. Preferably, the host matrix comprises, consists of, or consists essentially of one or more ESIPT materials selected from HBT , HBT-Cz, and mCP, more preferably, HBT. In some embodiments the host is F8BT [poly(9,9-dioctylfluorene-alt- benzothiadiazole)] .

[0021] In some embodiments, the host matrix comprises, consists of, or consists essentially of a combination of mCP and HBT. In some embodiments, the ratio of mCP to HBT is about 4:1 by weight.

[0022] In some embodiments, a composition is provided as a coating or a thin film, optionally the coating or thin film is provided on a substrate.

[0023] In some embodiments, a composition of the invention comprises a dye compound as defined herein. In some embodiments, the dye compound is present in a composition in an amount of 1-5% by weight, preferably about 2% by weight.

[0024] In some embodiments, a film or coating according to the invention has a thickness of about 120 nm to about 260 nm. [0025] In yet another aspect, the present invention provides a use of a dye compound or composition as described herein as an active gain medium, preferably for light amplification. In some embodiments, the active gain medium is for light amplification in organic solid-state lasers. In some embodiments, the active gain medium is for use in at least one of: organic solid-state lasers; opto-electronic applications; laser diodes; light-emitting diodes; solar cells; sensors; and photorefractive devices.

[0026] In a further aspect, there is provided a composition for use as an active gain medium for light amplification, the composition comprising a mixed host matrix including one or more host compounds and an organic dye emitter, wherein the one or more host compounds are configured to absorb pump energy at a pump wavelength, and transfer energy to the dye using a cascade energy transfer process so that the dye emits energy at an emission wavelength longer than the pump wavelength. In some embodiments, the cascade energy transfer process reduces a gap between energy transferred to the dye and energy emitted by the dye. In some embodiments, the cascade energy transfer process uses a Stokes shift in at least one host compound of the host matrix.

[0027] In some embodiments, at least one host compound is selected from the group consisting of excited-state intramolecular transfer (ESIPT) host materials. In some embodiments, the ESIPT material is selected from l,3-bis(/V-carbazolyl)benzene (mCP), 4,4'-bis(7V-carbazolyl)-l,r-biphenyl (CBP), 2-hydroxyphenylbenzothiazole (HBT), bcnzo[d]thiazol-2-yl)-5-(9//-carbazol-9-yl)phcnol (HBT-Cz), flavone, benzotriazole, poly(9-vinylcarbazole) (PVK) and 2-( 1 -(aryl)- 1 //-phcnanthro[9, 1 O-dJimidazol-2- yl)phenol. In some embodiments, the host compounds are a combination comprising 1,3- bis(7V-carbazolyl)bcnzcnc (mCP) and 2-hydroxyphenylbenzothiazole (HBT); or a combination comprising l,3-bis(/V-carbazolyl)benzene (mCP) and benzo[d]thiazol-2-yl)- 5-(9/ -carbazol-9-yl)phenol (HBT-Cz).

[0028] In some embodiments, the Stokes shift results from excited-state intramolecular proton transfer (ESIPT) in HBT. In some embodiments, the Stokes shift facilitates efficient cascade energy transfer from mCP to HBT. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1: (a) Absorption (dashed) and PL spectra (solid) of Cibalackrot A (black) and B (red) in toluene solution, (b) Solid state absorption and normalised PL spectra of 5wt% Cibalackrot A blended in different hosts [mCP, CBP and mCP:HBT (4: 1 by weight)] .

[0030] Figure 2: Normalised absorption (dashed lines) and PL (solid lines) spectra of neat-film Cibalackrot A and B overlapped with PL of neat-film mCP, CBP and mixed host (mCP:HBT).

[0031] Figure 3: TCSPC fluorescence decay for (a) Cibalackrot A and (b) Cibalackrot B blend films 1-5 wt% in mCP:HBT (4:1 by weight)]. Emission was monitored at 592 nm for Cibalackrot A and 605 nm for Cibalackrot B.

[0032] Figure 4: Normalised solution absorption and PL spectra of

Cibalackrot I in toluene.

[0033] Figure 5: Normalised solution absorption and PL spectra of

Cibalackrot Dimer E, F, G and H in toluene.

[0034] Figure 6: Normalised absorption and PL spectra of neat and blend films (0.5-8.0wt% in F8BT) of Cibalackrot Dimer E.

[0035] Figure 7 : Normalised absorption and PL spectra of neat and blend films

(0.5-8.0wt% in F8BT) of Cibalackrot Dimer F.

[0036] Figure 8: Transient absorption spectrum of Cibalackrot B in bromobenzene recorded at different time delays for pump intensity of 1.3 mw with triplet absorption spectra magnified in the inset.

[0037] Figure 9a: Evolution of emission intensity from ASE peak of 5wt% of Cibalackrot A blended in different host under optical pump intensity just below E _th (open circles, top) and 2 x Z¾ _i (solid lines, bottom).

[0038] Figure 9b: Spectral evolution for 5wt% Cibalackrot A doped in different hosts under pump intensity 2 x E*. Spectra post 1 and 100 seconds show retention of ASE in case of mixed host. Mixed host [mCP:HBT (4:1 by weight)].

[0039] Figure 10: (a) Input-output-FWHM and (b) spectral narrowing for 237 nm thick films of 3wt% of Cibalackrot A in mCP:HBT (4:1 by weight), (c) Input-output- FWHM and (d) spectral narrowing for 226 nm thick films of 2wt% Cibalackrot B in mCP:HBT (4:1 by weight).

[0040] Figure 11: Evolution of ASE peak wavelength intensity in 230 nm thick films of 2wt% Cibalackrot B doped in mCP:HBT (4:1 by weight) under pump intensity of 2 x Eth (~20 pj cm ² ). Inset: ASE spectrum post 10 and 9,000 pump pulses.

[0041] Figure 12: (a) Input-output-FWHM and (b) spectral narrowing for films of lwt% of Cibalackrot Dimer E in F8BT.

[0042] Figure 13: (a) Input-output-FWHM and (b) spectral narrowing for films of lwt% of Cibalackrot Dimer F in F8BT.

[0043] Figure 14: (a) Output intensity of DFB laser device plotted as a function of input pump excitation (inset: optical image of the output beam obtained on screen at pump excitation of 100 pj cm ² ) (b) Evolution of emission spectra of dfb laser with input pump excitation for 260 nm thick films of 2wt% Cibalackrot derivative in the mixed host.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

[0044] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, preferred methods and materials are described. For the purposes of the present invention, the following terms are defined below.

[0045] The articles "a" and "an" are used herein to refer to one or to more than one (i.e. to at least one) of the grammatical object of the article. By way of example, "an element" means one element or more than one element.

[0046] By "about" is meant a quantity, level, value, number, frequency, percentage, dimension, size, amount, weight or length that varies by as much as 10, 9, 8, 7, 6, 5, 4, 3, 2 or 1 % to a reference quantity, level, value, number, frequency, percentage, dimension, size, amount, weight or length. The term "approximately" is construed similarly. [0047] When used herein the terms "w/w%", "w/v%" and "v/v%" mean, respectively, weight to weight, weight to volume, and volume to volume percentages.

[0048] As used herein, the term "and/or" refers to and encompasses any and all possible combinations of one or more of the associated listed items, as well as the lack of combinations when interpreted in the alternative (or).

[0049] Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. Thus, the use of the term "comprising" and the like indicates that the listed integers are required or mandatory, but that other integers are optional and may or may not be present. By "consisting of" is meant including, and limited to, whatever follows the phrase "consisting of". Thus, the phrase "consisting of" indicates that the listed elements are required or mandatory, and that no other elements may be present. By "consisting essentially of" is meant including any elements listed after the phrase, and limited to other elements that do not interfere with or contribute to the activity or action specified in the disclosure for the listed elements. Thus, the phrase "consisting essentially of" indicates that the listed elements are required or mandatory, but that other elements are optional and may or may not be present depending upon whether or not they affect the activity or action of the listed elements.

[0050] Each embodiment described herein is to be applied mutatis mutandis to each and every embodiment unless specifically stated otherwise.

Abbreviations

[0051] As used herein the symbols and conventions used in these processes, schemes and examples are consistent with those used in the contemporary scientific literature, for example, the Journal of the American Chemical Society. Specifically the following abbreviations may be used in the specification:

[0052] ASE (amplified spontaneous emission); DFB (distributed feedback); ESIPT (excited-state intramolecular proton transfer); FRET (Forster resonance energy transfer); FWHM (full-width-at-half-maximum); HOMO (highest occupied molecular orbital); LUMO (lowest unoccupied molecular orbital); OSSL (organic solid-state laser); PL (photoluminescence); PLQY (photoluminescence quantum yields); TAS (transient absorption spectroscopy); TCSPC (time correlated single photon counting); CBP (4,4'- bis(7V-carbazolyl)-l , 1 '-biphenyl); DCM (dichloromethane); DMF (N,N'- dimethylformamide); HBT (2-hydroxyphenylbenzothiazole); HBT-Cz (benzo[d]thiazol- 2-yl)-5-(9H-carbazol-9-yl)phenol); IPA (isopropanol, 2-propanol); mCP (l,3-bis(/V- carbazolyl)benzene); MIBK (methyl isobutyl ketone, 4-methyl-2-pentanone); PVK (poly(9-vinylcarbazole); THF (tetrahydrofuran).

Compounds of the Invention

[0053] The compounds of the invention are organic semiconductor laser dyes with deep-red emission in the region of approximately 570 - 700 nm of the electromagnetic spectrum. In accordance with characterisation according to CIEs (1931 Commission Internationale de l'Eclairage coordinates), the dye coordinates place them in the deep-red region of the 1931 CIE RGB colour space chart. These laser dyes have improved solubility by virtue of the presence of solubilising groups and are thus solution processable. This facilitates solution deposition of the dyes, making them amenable to conventional techniques for coating and film formation. In at least some examples, the dyes have been found to demonstrate excellent PLQYs, with high solution PLQYs close to unity. Low ASE thresholds have also been demonstrated. In use, the dyes have been shown to have high photo stability and thermal stability and reversible redox profiles.

[0054] According to a first aspect, the present invention provides a compound of Formula (I): wherein: represents an aryl or heteroaryl moiety; each R ¹ may be the same or different and is independently selected from the group consisting of optionally substituted alkyl, optionally substituted alkoxy, optionally substituted alkylenearyl, halogen and a group having the structure: integer from 1 to 5; each R ² may be the same or different and is independently selected from the group consisting of halogen and optionally substituted aryl; x is an integer from 1 to 3; and y is an integer from 0 to 4.

[0055] Hereinafter, the [¾ ring may , for convenience, be referred to as "A" or the "A ring".

[0056] In some embodiments, A is aryl, preferably phenyl. In some embodiments, A is furanyl, thiophenyl, pyrrolyl, carbazolyl, pyridyl or imidazolyl.

[0057] R ¹ is a substituent on the A ring in the compound of Formula (I). Where there are two or more R ¹ groups present, each instance of R ¹ in the compounds of Formula (I) may be the same or different and may be an optionally substituted alkyl group or optionally substituted alkoxy group. When the A ring is phenyl, the R ¹ may be located at the ortho , meta or para positions of the phenyl ring in the compound of Formula (I), with respect to the carbon atom by which the phenyl ring is attached.

[0058] In some embodiments, R ¹ is an optionally substituted alkyl group. The alkyl group may be a C3-C30 alkyl group. In an embodiment, R ¹ is a C3-C24 alkyl group. In an embodiment, R ¹ is a C6-C24 alkyl group. In another embodiment, R ¹ is a C6-C20 alkyl group. In another embodiment, R ¹ is a C ₆ -Cis alkyl group. In another embodiment, R ¹ is a C6-C16 alkyl group. In another embodiment, R ¹ is a C6-C14 alkyl group. In another embodiment, R ¹ is a C6-C12 alkyl group. In another embodiment, R ¹ is a C8-C12 alkyl group. In another embodiment, R ¹ is a C10-C12 alkyl group. In a preferred embodiment, R ¹ is a C12 alkyl group.

[0059] In some embodiments, R ¹ is a C3-C30 alkyl group that may be straight chain or branched. In an embodiment, R ¹ is a straight chain alkyl group. In an embodiment, R ¹ is a straight chain C6-C30 alkyl group. In an embodiment, R ¹ is a straight chain C ₆ -C ₂₀ alkyl group. In another embodiment, R ¹ is a straight chain C6-Cis alkyl group. In another embodiment, R ¹ is a straight chain C ₆ -C ₁₆ alkyl group. In another embodiment, R ¹ is a straight chain C ₆ -C ₁₄ alkyl group. In another embodiment, R ¹ is a straight chain C ₆ -C ₁₂ alkyl group. In another embodiment, R ¹ is a straight chain C ₈ -C ₁₂ alkyl group. In another embodiment, R ¹ is a straight chain C ₁₀ -C ₁₂ alkyl group. In a preferred embodiment, R ¹ is a straight chain C ₁₂ alkyl group. In an embodiment, R ¹ is branched chain alkyl group. In an embodiment, R ¹ is a branched chain C ₆ -C ₂₀ alkyl group. In another embodiment, R ¹ is a branched chain C ₆ -C ₁₈ alkyl group. In another embodiment, R ¹ is a branched chain C ₆ -C ₁₆ alkyl group. In another embodiment, R ¹ is a branched chain C ₆ -C ₁₄ alkyl group. In another embodiment, R ¹ is a branched chain Ce- C ₁₂ alkyl group. In another embodiment, R ¹ is a branched chain C ₈ -C ₁₂ alkyl group. In another embodiment, R ¹ is a branched chain C ₁₀ -C ₁₂ alkyl group.

[0060] In some embodiments, R ¹ is an optionally substituted alkoxy group. The alkoxy group may be a C ₃ -C ₃₀ alkoxy group. In an embodiment, R ¹ is a C ₃ -C ₂₀ alkoxy group. In another embodiment, R ¹ is a C ₆ -C ₂₀ alkoxy group. In another embodiment, R ¹ is a C ₆ -C ₁₈ alkoxy group. In another embodiment, R ¹ is a C ₆ -C ₁₆ alkoxy group. In another embodiment, R ¹ is a C ₆ -C ₁₄ alkoxy group. In another embodiment, R ¹ is a C ₆ -C ₁₂ alkoxy group. In another embodiment, R ¹ is a C ₈ -C ₁₂ alkoxy group. In another embodiment, R ¹ is a C ₁₀ -C ₁₂ alkoxy group. In a preferred embodiment, R ¹ is a Cs alkoxy group. In a preferred embodiment, R ¹ is a C ₁₀ alkoxy group. In preferred embodiment, R ¹ is a C ₁₂ alkoxy group. In a preferred embodiment, R ¹ is C ₂₀ alkoxy group.

[0061] In some embodiments, R ¹ is a C ₃ -C ₃₀ alkoxy group that may be straight chain or branched. In an embodiment, R ¹ is a straight chain alkoxy group. In an embodiment, R ¹ is a straight chain C ₆ -C ₃₀ alkoxy group. In another embodiment, R ¹ is a straight chain C ₆ -C ₁₈ alkoxy group. In another embodiment, R ¹ is a straight chain C ₆ -C ₁₆ alkoxy group. In another embodiment, R ¹ is a straight chain C ₆ -C ₁₄ alkoxy group. In another embodiment, R ¹ is a straight chain C ₆ -C ₁₂ alkoxy group. In another embodiment,

R ¹ is a straight chain C ₈ -C ₁₂ alkoxy group. In another embodiment, R ¹ is a straight chain

C ₁₀ -C ₁₂ alkoxy group. In a preferred embodiment, R ¹ is a straight chain C ₁₀ alkoxy group.

In a preferred embodiment, R ¹ is a straight chain C ₁₂ alkoxy group. In an embodiment,

R ¹ is branched chain alkoxy group. In an embodiment, R ¹ is a branched chain C ₆ -C ₂₀ alkoxy group. In another embodiment, R ¹ is a branched chain C ₆ -C ₁₈ alkoxy group. In another embodiment, R ¹ is a branched chain C ₆ -C ₁₆ alkoxy group. In another embodiment, R ¹ is a branched chain C ₆ -C ₁₄ alkoxy group. In another embodiment, R ¹ is a branched chain C ₆ -C ₁₂ alkoxy group. In another embodiment, R ¹ is a branched chain C ₈ -C ₁₂ alkoxy group. In another embodiment, R ¹ is a branched chain C ₁₀ -C ₁₂ alkoxy group. In a preferred embodiment, R ¹ is branched chain Cs alkoxy group. In a preferred embodiment, R ¹ is a branched chain C ₂₀ alkoxy group.

[0062] In some embodiments, R ¹ is an alkyenearyl group. In an embodiment, R ¹ is an alkylenearyl group, where the alkylene group is straight chain or branched. In an embodiment, R ¹ is an alkylenearyl group where the alkylene group is a straight chain group. In an embodiment, R ¹ is an alkylenearyl group where the alkylene group is a branched chain group. In an embodiment, R ¹ is a (Ci-C ₃ o)alkylenearyl group. In another embodiment, R ¹ is a (C ₃ -C ₃ o)alkylenearyl group In another embodiment, R ¹ is a (C ₆ - C ₂₄ )alkylenearyl group. In another embodiment, R ¹ is a (C ₈ -Ci ₂ )alkylenearyl group. In an embodiment, R ¹ is an alkylene(C ₆ -Ci ₄ )aryl group. In another embodiment, R ¹ is an alky lene(C6) aryl group. In an embodiment, R ¹ is a (C ₃ -C ₃ o)alkylene(C ₆ -Ci ₄ )aryl group. In an embodiment, R ¹ is a (C ₆ -C ₂₄ )alkylene(C ₆ -Ci ₄ )aryl group. In an embodiment, R ¹ is a (C ₃ -C ₃ o)alkylene(C ₆ )aryl group.

[0063] In some embodiments, R ¹ is a halogen group. In an embodiment, R ¹ is fluorine. In an embodiment, R ¹ is chlorine. In an embodiment, R ¹ is bromine. In an embodiment, R ¹ is iodine. In some embodiments, when A is phenyl, R ¹ is a halogen group at the para position of the phenyl ring. In an embodiment, when A is phenyl, R ¹ is a chlorine group at the para position. In an embodiment, when A is phenyl, R ¹ is bromine group at the para position. In a preferred embodiment, when A is phenyl, R ¹ is an iodine group at the para position of the phenyl ring. In some embodiments, R ¹ is not a halogen group. In some embodiments, a compound of Formula (I) has one substituent where R ¹ is halogen.

[0064] In some embodiments, R ¹ is a group having the structure , which is a polyethoxy group, where z is an integer from 1 to 5. Groups having this structure may also be known as polyethoxylene groups, when more than one ethoxy group is present. In an embodiment, z is 1. In another embodiment, z is 2. In another embodiment, z is 3. In another embodiment, z is 4. In another embodiment, z is 5. [0065] In some embodiments, x is an integer from 1 to 3. For example, x may be 1, 2 or 3. Each instance of x in the compound of Formula (I) may be the same or different. Where each instance of x in the compound of Formula (I) is the same, the compound may have a plane of symmetry. In an embodiment, x is 1. In an embodiment, when A is phenyl, x is 1 and the group R ¹ is at the para position of the ring on which R ¹ is located. In an embodiment, when A is phenyl, x is 1 and the group R ¹ is at the meta position of the ring on which R ¹ is located. In a preferred embodiment, x is 1 in both instances in the compound of Formula (I). In a preferred embodiment, when A is phenyl, x is 1 and the group R ¹ is at the para position of the ring on which R ¹ is located in each instance of x and R ¹ in the compound of Formula (I).

[0066] R ² is a substituent on the fused phenyl ring in the compound of Formula (I). Where there are more than one R ² groups present, each R ² may be the same or different and may be halogen or optionally substituted aryl.

[0067] In some embodiments, R ² is a halogen group. In an embodiment, R ² is fluorine. In an embodiment, R ² is chlorine. In an embodiment, R ² is bromine. In an embodiment, R ² is iodine.

[0068] In some embodiments, R ² is an optionally substituted aryl group. In an embodiment, R ² is a phenyl group.

[0069] In some embodiments, y is an integer from 0 to 4. For example, y may be 0, 1, 2, 3 or 4. Each instance of y in the compound of Formula (I) may be the same or different. Where each instance of y in the compound of Formula (I) is the same, the compound may have a plane of symmetry. In an embodiment, y is 0. Where y is 0, the fused phenyl ring on which the group R ² is located in the compound of Formula (I) is unsubstituted. In an embodiment, each instance of y is 1.

[0070] In some embodiments, n is 0 in each instance such that the fused phenyl ring in the compound of Formula (I) is unsubstituted and the compound of Formula (I) has the structure of Formula (la):

Formula (la) wherein , R ¹ and x have the definitions as defined above.

In some embodiments, each is phenyl.

[0071] In some embodiments, A is phenyl and x is 1 in each instance and each substituent R ¹ is at the para position of the phenyl ring in the compound of Formula (la) such that the compound has the structure of Formula (lb):

Formula (lb) wherein R ¹ has the definitions as defined above.

[0072] In a preferred embodiment of the compound of Formula (I) or (G), R ¹ is a linear C3-C20 alkyl group. In a preferred embodiment, R ¹ is a Cs-Cn alkyl group. In another preferred embodiment, R ¹ is a C12 alkyl group.

[0073] In a preferred embodiment, the compound of Formula (I) or (G) has the following structure:

[0074] In another preferred embodiment of the compound of Formula (I) or (G), R ¹ is a linear C ₃ -C ₂₀ alkoxy group. In a preferred embodiment, R ¹ is a linear C ₁₀ -C ₁₂ alkoxy group. In a preferred embodiment, R ¹ is a linear C10 alkoxy group.

[0075] In a preferred embodiment, the compound of Formula (I) has the following structure:

[0076] The above compound structure has the systematic name of 7,14-bis(4- dodecylphenyl)diindolo[3,2,l-de:3',2',r-ij][l,5]naphthyridin e-6,13-dione.

[0077] In another preferred embodiment of the compound of Formula (I) or (G), R ¹ is branched C3-C30 alkoxy group. In a preferred embodiment, R ¹ is a branched C20 alkoxy group. In another preferred embodiment, R ¹ is a branched Cs alkoxy group.

[0078] In a preferred embodiment, the compound of Formula (I) or (G) has the following structure:

[0079] In another preferred embodiment, the compound of Formula (I) or (G) has the following structure:

[0080] The above compound structure has the systematic name of 7,14-bis(4- ((2-ethylhexyl)oxy) phenyl)diindolo[3,2,l-de:3',2',r-ij][l,5]naphthyridine-6,13- dione

[0081] In another preferred embodiment, R ¹ is a polyethoxy group. In a preferred embodiment, R has the structure , where z is 3.

[0082] In another preferred embodiment, the compound of Formula (I) has the following structure:

[0083] The present inventors have found that the compounds of the present invention are useful as deep-red organic dyes owing to the extended conjugation throughout the compounds. Without wishing to be bound by theory, the present inventors believe that compounds that are dimers of the compounds of Formula (I) bound together by a linker, for example an aromatic linker, have the same or enhanced physical properties as those observed for compounds of Formula (I).

[0084] According to a second aspect, the present invention provides compounds of Formula (II), which are dimers of the compounds of Formula (I) connected by a linker: compounds of Formula (I) above.

[0085] In some embodiments, each (¾ (A) moiety is phenyl. In some embodiments, two of the A moieties attached to the L group are each furanyl.

[0086] Definitions of R ¹ , R ² , x and y for compounds of Formula (I) provided herein apply mutatis mutandis to compounds of Formula (II). [0087] L is a linker that joins two monomers having the structure of Formula (I) in order to provide compounds of Formula (II). As the compounds of Formula (II) are also useful as organic dyes, maintaining the extended conjugation of the compounds requires that the linker is also conjugated.

[0088] In some embodiments, the linker L is an arylene group. In an embodiment, the linker L is a 5- to 14-membered arylene group. In an embodiment, the linker L is a monocyclic arylene group. In another embodiment, the linker L is a bicyclic arylene group. In an embodiment, the linker L is a carbocyclic arylene group. In an embodiment, the linker L is a Ce arylene group. In another embodiment, the linker L is a Ce arylene group that is bound at the 1- and 4-positions. In another embodiment, the linker L is a Ce arylene group that is bound at the 1- and 3-positions. In some embodiments, the linker L is a heteroarylene group.

[0089] In an embodiment, the linker L is a 5- to 14-membered heteroarylene group. In an embodiment, the linker L is a heteroarylene group containing 1 heteroatom. In another embodiment, the linker L is a heteroarylene group containing 2 heteroatoms. In another embodiment, the linker L is a heteroarylene group containing 3 heteroatoms. In another embodiment, the linker L is a heteroarylene group containing more than 3 heteroatoms. In an embodiment, the linker L is a monocyclic heteroarylene group. In an embodiment, the linker L is a bicyclic heteroarylene group. In an embodiment, the linker L is a benzofused bicyclic heteroarylene group. In an embodiment, the linker L is a benzofused bicyclic heteroarylene group that is bound to the monomers of Formula (I) through the benzofused portion of the linker.

[0090] In some embodiments, the linker L is an optionally substituted arylene group. In an embodiment, the linker L is a 5- to 14-membered arylene group. In an embodiment, the linker L is an optionally substituted Ce arylene group. In another embodiment, the linker L is a Ce arylene group that is substituted at the 2- and 3-positions. In another embodiment, the linker L is a Ce arylene group

[0091] In some embodiments, the linker L contains multiple arylene groups joined sequentially. In an embodiment, the linker L contains two arylene groups. In an embodiment, the linker L contains three arylene groups. In an embodiment, the linker L contains 4 arylene groups. In another embodiment, the linker contains 5 or more arylene groups. [0092] In an embodiment, the linker L contains two phenylene groups sequentially. In another embodiment, the linker L contains two phenylene groups joined to the monomers of Formula (I) and each at the 1- and 4-positions of the phenylene rings. In another embodiment, the linker L contains two phenylene groups that are each independently optionally substituted. In another embodiment, the linker L contains two phenylene groups that are independently substituted by an alkyl group, preferably a C3- C20 alkyl group. In another embodiment, the linker L contains two phenylene groups that are independently substituted by C7 alkyl groups. In another embodiment, the linker L contains two phenylene groups substituted by C7 alkyl groups, where the C7 alkyl groups are joined such that the phenylene groups and the alkyl groups form a fused polycyclic moiety.

[0093] In an embodiment, the linker L is a fused polycyclic moiety derived from alkyl-substituted phenylene groups. In another embodiment, the linker L contains multiple fused polycyclic moieties derived from alkyl-substituted phenylene groups. In an embodiment, the linker L that is a fused polycyclic moiety derived from alkyl- substituted phenylene-groups is derived from fluorene. In an embodiment, the linker L is a fluorenylene group. In another embodiment, the linker L contains multiple fluorenylene groups joined sequentially. In another embodiment, the linker L contains an optionally substituted fluorenylene group. In another embodiment, the linker L contains an alkyl- substituted fluorenylene group. In another embodiment, the linker L contains multiple alkyl-substituted fluorenylene groups.

[0094] In some embodiments of compounds of Formula (II), each y is 0.

[0095] In some embodiments, the compound of Formula (II) is a compound of

Formula (Ila):

Formula (Ila) wherein: L is an arylene group as defined above, and and R ¹ is as defined above for compounds of Formula (I) or Formula (II).

[0096] In some embodiments, two of the A rings are phenyl and the other two are furanyl, x is 1 in each instance and each substituent R ¹ is at the para position of the phenyl ring in the compound of Formula (II) such that the compound has the structure of Formula (lib): wherein:

L is an arylene group as defined above, and R ¹ is as defined above for compounds of Formula (1) or Formula (II).

[0097] In some embodiments, each A ring is phenyl, x is 1 in each instance and each substituent R ¹ is at the para position of the phenyl ring in the compound of Formula (II) such that the compound has the structure of Formula (lie):

Formula (lie) wherein:

L is an arylene group as defined above, and R ¹ is as defined above for compounds of Formula (I) or Formula (II). [0098] Preferred embodiments of the linker L include:

[0099] As used herein, the term "alkyl" is taken to include straight chain or branched chain monovalent saturated hydrocarbon groups, preferably having 3 to 20 carbon atoms. Examples of a straight chain alkyl group includes propyl, butyl, pentyl, hexyl, heptyl, octyl, dodecyl, and the like. Examples of a branched chain alkyl group includes isopropyl, isobutyl, sec-butyl, tert-butyl, iso-pentyl, neo-pentyl, and the like. [00100] As used herein, the term "alkylene" refers to bivalent group derived from the removal of a hydrogen atom from two different carbon atoms of an alkyl group. The bivalent alkylene group has two points of attachments to other groups. As used herein, the term "alkylenearyl" refers to a bivalent alkylene group having one point of attachment to an aryl group and the other point of attachment to the remainder of the compound.

[00101] As used herein, the term "alkoxy group" is taken to include -O-alkyl groups, i.e. alkyl groups bound to an oxygen atom, preferably where the alkyl group has 3 to 20 carbon atoms. The alkoxy group may be straight chain or branched chain alkoxy groups. Examples of a straight chain alkoxy group includes propoxy, butoxy, pentoxy, hexyloxy, heptyloxy, octyloxy, dodecoxy and the like. Examples of a branched chain alkoxy group include (2-ethylhexyl)oxy.

[00102] As used herein, the term "aryl" refers to a monovalent unsaturated aromatic carbocyclic group having a single ring (e.g. phenyl) or multiple condensed rings (e.g. naphthyl, anthracenyl), preferably having from 6 to 14 carbon atoms. Examples of aryl groups include phenyl, naphthyl, anthracenyl and the like. Where one or more carbon atoms of the aryl group is replaced with one or more heteroatoms, the group is a heteroaryl group. The heteroatoms may be selected from nitrogen, oxygen and sulphur. Examples of heteroaryl groups include furanyl, quinazolinyl, quinolinyl, isoquinolinyl, indolyl, isoindolyl, benzopyranyl, benzooxazolyl, benzimidazolyl, pyrazolyl, tetrazolyl, oxazolyl, oxadiazolyl, isoxazolyl, thiadiazolyl, quinolizinyl, pyranyl, isothiazolyl, thiazolyl, thienyl (thiophenyl), imidazolyl, pyrazinyl, pyridazinyl, pyrimidinyl, isothiazolyl, pyridyl, triazolyl, benzothienyl, pyrrolyl, benzothiazolyl, quinoxalinyl, naphthyridinyl, pteridinyl, carbazolyl, azepinyl, acridinyl, benzisothiazolyl, benzoxazolyl, benzisoxazolyl, benzofuryl, purinyl, benzimidazolyl, triazinyl, carbazolyl, and the like.

[00103] As used herein, the term "arylene" generally refers to a bivalent group derived from the removal of a hydrogen atom from two ring carbon atoms from an aromatic group. An example of an arylene group includes a phenylene ring, which is a divalent group having 6 carbon atoms in an aromatic ring, in which two hydrogen atoms are removed. Accordingly, the term "heteroarylene" refers to a divalent arylene group where one or more carbon atoms is replaced with one or more heteroatoms. [00104] As used herein, the term "halogen" refers to a fluorine, chlorine, bromine or iodine group.

[00105] As used herein, the term "optionally substituted" as used throughout the specification denotes that the group may or may not be further substituted or fused (so as to form a condensed polycyclic system), with one or more non-hydrogen substituent groups. In certain embodiments the substituent groups are one or more groups independently selected from the group consisting of halogen, =0, =S, -CN, -NO ₂ , -CF ₃ , -OCF ₃ , alkyl, alkenyl, alkynyl, alkoxy, haloalkyl, haloalkenyl, haloalkynyl, haloalkoxy, heteroalkyl, cycloalkyl, cycloalkenyl, heterocycloalkyl, heterocycloalkenyl, aryl, heteroaryl, cycloalkylalkyl, heterocycloalkylalkyl, heteroarylalkyl, arylalkyl, cycloalkylalkenyl, heterocycloalkylalkenyl, arylalkenyl, heteroarylalkenyl, cycloalkylheteroalkyl, heterocycloalkylheteroalkyl, arylheteroalkyl, heteroarylheteroalkyl, hydroxy, hydroxyalkyl, alkyloxy, alkyloxyalkyl, alkyloxycycloalkyl, alkyloxyheterocycloalkyl, alkyloxyaryl, alkyloxyheteroaryl, alkyloxycarbonyl, alkylaminocarbonyl, alkenyloxy, alkynyloxy, cycloalkyloxy, cycloalkenyloxy, heterocycloalkyloxy, heterocycloalkenyloxy, aryloxy, phenoxy, benzyloxy, heteroaryloxy, arylalkyloxy, amino, alkylamino, acylamino, aminoalkyl, arylamino, sulfonylamino, sulfinylamino, sulfonyl, alkylsulfonyl, arylsulfonyl, aminosulfonyl, sulfinyl, alkylsulfinyl, arylsulfinyl, aminosulfinylaminoalkyl and carbonyl.

[00106] In some embodiments each optional substituent is independently selected from the group consisting of: halogen, =0, =S, -CN, -NO ₂ , -CF ₃ , -OCF ₃ , alkyl, alkenyl, alkynyl, haloalkyl, haloalkenyl, haloalkynyl, heteroalkyl, cycloalkyl, cycloalkenyl, heterocycloalkyl, heterocycloalkenyl, aryl, heteroaryl, hydroxy, hydroxyalkyl, alkyloxy, alkyloxyalkyl, alkyloxyaryl, alkyloxyheteroaryl, alkenyloxy, alkynyloxy, cycloalkyloxy, cycloalkenyloxy, heterocycloalkyloxy, heterocycloalkenyloxy, aryloxy, heteroaryloxy, arylalkyl, heteroarylalkyl, arylalkyloxy, amino, alkylamino, acylamino, aminoalkyl, arylamino, sulfonyl, alkylsulfonyl, arylsulfonyl, aminosulfonyl, aminoalkyl, COOH, SH, and acyl.

[00107] Examples of particularly suitable optional substituents include F, Cl, Br, I, CH , CH ₂ CH ₃ , w-dodecyl, (2-ethylhexyl)oxy, phenyl, OH, OCH , CF , OCF , N0 ₂ , NH2 and CN. Other optional substituents include aryl, including phenyl, and alkyaryl, including alkylphenyl, and alkoxyaryl, including alkoxy phenyl.

[00108] As used herein, the term "alkenyl" refers to a monovalent aliphatic carbocyclic group having at least one carbon-carbon double bond and which may be straight chained or branched, preferably having from 2 to 10 carbon atoms. Examples of such groups include a vinyl or ethenyl group (-CH=CH2), n-propenyl (-CH2CH=CH2), iso-propenyl (-0(ϋ¾)=OH ₂ ), but-2-enyl (-CH2CH=CHCH3), and the like.

[00109] As used herein, the term "alkynyl" refers to a monovalent aliphatic carbocyclic group having at least one carbon-carbon triple bond and which may be straight chained or branched, preferably having from 2 to 10 carbon atoms. Examples of such groups include an acetylene or ethynyl group (-CºCH), propargyl (-CH2CºCH), and the like.

[00110] As used herein, the term "cycloalkyl" refers to a saturated monocyclic or fused or spiro polycyclic carbocycle preferably containing from 3 to 12 carbons per ring, such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl and the link, unless otherwise specified. Monocyclic cycloalkyl groups include cyclopentyl and cyclohexyl, bicyclic cycloalkyl groups include decalin and polycyclic cycloalkyl groups include adamantane. Preferred cycloalkyl groups are C ₃ to C ₉ cycloalkyl groups.

[00111] In some embodiments, preferably the dye compound is: wherein:

R ¹ = 77-dodccyl (Cibalackrot A); or R ¹ = 2-ethylhexyloxy (Cibalackrot B).

[00112] Cibalackrot A is systematically named as 7,14-bis(4-dodecyl- phenyl)diindolo[3,2,l-de:3',2',r-ij][l,5]naphthyridine-6,13- dione. Cibalackrot B is systematically named as 7,14-bis(4-((2-ethylhexyl)oxy) phenyl)diindolo[3,2,l-de:3',2',r- ijj[ 1 ,5Jnaphthyridinc-6, 13-dionc.

[00113] In use, it will be appreciated that the dyes can be used as part of a mixture of dyes. In some embodiments, a compound of Formula (I) or Formula (II) may be used in the form of a mixture comprising two or more dye compounds, such as red or deep-red dye compounds. The one or more dyes may be in any ratio in accordance with the physical and chemical properties required. Those skilled in the art will readily be able to determine the identity and ratios of the dye compounds depending on the circumstances. In some embodiments, the dye compounds in such a mixture are selected from compounds of Formula (I) or Formula (II). In some examples, the dye mixture comprises a combination of Cibalackrot A and Cibalackrot B.

[00114] It will be appreciated that, with regard to the compounds of Formula (G) and Formula (IF) as defined herein, the ring moiety to which each of the R ¹ substituents is attached is a phenyl ring. It will be understood that compounds of Formula (I) or compounds of Formula (II) where at least one of these phenyl rings is replaced by an aryl ring, and in particular a heteroaryl ring, may also have utility as a dye in accordance with the present invention. Examples of alternative aryl rings include furanyl, thiophenyl, pyrrolyl, carbazolyl, pyridyl or imidazolyl.

Compositions of the Invention

[00115] For use as a dye for laser technology, Those skilled in the art will understand that a dye compound of Formula (I) or Formula (II) may be used on its own. Thus, the dye may be processed or formulated in accordance with the requirements of its intended use in the absence of any other material such as substrate, binders, plasticisers, polymeric matrices, host matrices, and the like.

[00116] The compounds of Formula (I) and Formula (II) are soluble in one or more solvents, and thus may be formulated in solution. In some embodiments, the dye compound may be cast or deposited from solution and the solvent allowed to evaporate to provide a film or coating, such as a thin film. In some examples, the compound of Formula (I) or Formula (II) is suitably provided as a coating on a substrate. Examples of suitable substrates are well known in the art and will depend on the application. In some embodiments, a substrate is fused silica. [00117] Determination of a suitable solvent (or solvent combination) to form a coating solution comprising a dye compound of the invention is well within the skill and knowledge in the art. In some examples, the film or coating is deposited from chloroform solution. Methods of coating are well known in the art and may be selected in accordance with the particular application and circumstances. Examples of methods of coating or casting films include, for example, spin-coating, blade coating or hand coating using, for example, a K bar. Other examples include ink-jet printing or spray deposition.

[00118] In another aspect, the present invention thus provides a coating or film comprising a compound of Formula (I) or Formula (II). In some embodiments, the compound of Formula (I) is Cibalackrot A or Cibalackrot B.

[00119] The required thickness of a coating or film will depend on its intended application. It will be appreciated that the thickness of a coating or film can be controlled by modification of factors during its preparation. In some embodiments, the film thickness can be controlled by altering the speed of rotation during spin coating, or by altering the concentration of the coating solution. Examples of coating solution concentrations include from about 20 mg mF ¹ to about 30 mg mF ¹ of a dye compound of Formula (I) or (II) in chloroform. In some embodiments, the film or coating is a thin film with a thickness of about 100 nm to about 300 nm; for example from about 120 nm to about 260 nm, or about 140-150 nm. In some examples, a thin film comprising a compound of Formula (I) or (II) may be spin coated from a 20 mg mF ¹ chloroform solution at 1,500 rpm on a fused silica substrate to obtain film thickness of about 140- 150 nm.

[00120] In some embodiments, the film or coating is flexible. It will be appreciated that, if required, the coating solution may additionally comprise additives such as plasticisers to improve or modify the physical properties of the film. The selection of any additives will be well within the knowledge of those skilled in the art.

[00121] In some preferred embodiments a dye compound of Formula (I) or Formula (II) is suitably formulated with one or more additional components. In some embodiments, the dye compound and additional components are combined in a matrix, suitably in a solution, prior to depositing as a film or coating. [00122] It has been discovered that the properties of a dye compound of Formula (I) or Formula (II) when used as an active gain medium for lasers may be enhanced when combined with a host substance to form a guest (dye):host matrix.

[00123] A host, host substance, host compound or host matrix as referred to herein means a material that, in use, can absorb high pump energy at the pump wavelength and then can transfer energy to the dye through Forster resonance energy transfer (FRET).

[00124] Accordingly, in a further aspect, the present invention advantageously provides a composition comprising: a compound of Formula (I) or Formula (II) as defined herein; and a host matrix.

[00125] Examples of host substances typically used in host matrices in the field of laser technology are known in the art. In some preferred embodiments, the host matrix comprises one or more excited-state intramolecular transfer (ESIPT) host substances. Examples of ESIPT materials are known in the art. In some embodiments, a host substance is an EISPT material selected from, but not limited to, l,3-bis(/V- carbazolyl)benzene (mCP), 4,4'-bis(/V-carbazolyl)-l,l'-biphenyl (CBP), 2- hydroxyphenylbenzothiazole (HBT), bcnzo[d]thiazol-2-yl)-5-(9/7-carbazol-9-yl)phcnol (HBT-Cz), flavone, benzotriazole, and 2-(l-(aryl)-l//-phenanthro[9,10-d]imidazol-2- yl)phenol. A further example of a host substance is poly(9-vinylcarbazole) (PVK).

[00126] Dyes emitting in the longer red or deep-red wavelengths typically have long chromophores. The p-orbitals of the extended dye chromophore can result in strong p-p stacking in the solid state resulting in low photoluminescence quantum yields (PLQYs). This is due to aggregate induced luminescence quenching. It is known in the art that use of dye-matrix compositions can function as a guest-host combination that may, at least in part, address this issue. Guest-host combinations are beneficial for allowing advantageous energy transfer processes where the host (matrix) absorbs high pump energy and then transfers to the guest through Forster resonance energy transfer (FRET) to promote high stability of the laser dyes.

[00127] The present inventors have discovered that certain guest-host combinations comprising a dye compound (guest) and a host are particularly advantageous. In some embodiments, certain host materials facilitate improvement in the photostability or thermal stability of the dye molecule. In some embodiments, the host material comprises one or more excited-state intramolecular transfer (ESIPT) host materials.

[00128] An exemplary host substance is 2-hydroxyphenylbenzothiazole (HBT). The present inventors have discovered that the use of HBT as a host can result in energy transfer at a longer wavelength (lower energy region) from HBT to dyes such as those of Formulae (I) or (II). This is believed to be due, at least in part, to the large Stokes shift of HBT, i.e., a large difference in wavelength between the band maxima of the absorption and emission spectra. The large Stokes shift of HBT is believed to arise from excited- state intramolecular proton transfer (ESIPT) which results in conversion of the HBT from its enol form to a keto tautomer. This can facilitate efficient cascade energy transfer from the pump to the dye (emitter).

[00129] The present inventors have also discovered that the use of a mixed host comprising two or more host substances, particularly a mixed host comprising HBT, to be a preferred embodiment. In particular, a combination of the host substances mCP and HBT has been found to be particularly advantageous. This host combination has been identified as being particularly efficient with respect to cascade energy transfer from the pump to the dye.

[00130] Use of the mixed host leads to sufficient absorption at the pump wavelength with efficient energy transfer to the emitter, as well as a reduced gap between energy transferred and energy emitted by the dye. Hence, leading to lower heat dissipation in the emitter via non-radiative processes.

[00131] Accordingly, in another aspect, the present invention provides a composition for use as an active gain medium for light amplification, the composition comprising a mixed host matrix including one or more host compounds and an organic dye emitter, wherein the one or more host compounds are configured to absorb pump energy at a pump wavelength, and transfer energy to the dye using a cascade energy transfer process so that the dye emits energy at an emission wavelength longer than the pump wavelength.

[00132] In some embodiments, the cascade energy transfer process reduces a gap between energy transferred to the dye and energy emitted by the dye. In some embodiments, the cascade energy transfer process uses a Stokes shift in at least one host compound of the host matrix. Preferably a host compound is HBT. [00133] In some embodiments, the dye is a deep-red emitter, such as a compound of Formula (I) or Formula (II). A combination of mCP and HBT is a preferred mixed host for dye compounds, such as deep-red dye compounds. In some preferred embodiments, the dye is a compound of Formula (I) or Formula (II). It has been identified that the use of a mixed host, for example, mCP:HBT enables efficient cascade energy transfer and suppresses competitive aggregate induced fluorescence quenching.

[00134] Without being bound by theory or mode of operation, it is believed that the use of a mixed host can facilitate efficient cascading energy transfer from the pump to the dye emitter. The cascade transfer from mCP HBT emitter (dye) leads to high photostability of the dyes both below and above the amplified spontaneous emission (ASE) threshold pumping. Both of the single component hosts showed broadening of the spectrum as a signature of transition from ASE to spontaneous emission after 100-200 pump pulses. Improved photostability in mCP:HBT mixed host can be attributed to energy transfer at a longer wavelength (lower energy region) from HBT to a compound of Formula (I). The large Stokes shift of HBT, resulting from excited-state intramolecular proton transfer (ESIPT), allows efficient cascade energy transfer from mCP to HBT and then to the dye. It is believed that this contributes to high photo stability of the laser thin films when compared to single host systems of mCP or CBP. TAS measurements showed exceptionally low triplet yield and hence low triplet excited-state absorption in the gain window. It is believed that use of the mixed host leads to sufficient absorption at the pump wavelength with efficient energy transfer to the emitter, as well as a reduced gap between energy transferred and energy emitted by the dye. Hence, leading to lower heat dissipation in the dye via non-radiative processes.

[00135] In some embodiments, for compositions, coatings and films comprising dye compounds of Formulae (I) or (II), a preferred host matrix comprises HBT-Cz, HBT or mCP, preferably HBT or mCP. In some preferred embodiments, the host matrix comprises, consists of, or consists essentially of, a combination of HBT and mCP. In some embodiments, the host matrix comprises, consists of, or consists essentially of, a combination of HBT-Cz and mCP. In some embodiments, the ratio of mCP:HBT or mCP:HBT-Cz is from about 10:1 to about 1:1 by weight, for example 7:1 to about 2:1; 5:1 to about 3:1; or about 4:1 by weight. In some embodiments, the host is F8BT [poly(9,9-dioctylfluorene-alt-benzothiadiazole)]. [00136] The amount of dye present in the host matrix will depend on the identity of the dye and the requirements of the application. Those skilled in the art will be able to determine suitable amounts of dye depending on the circumstances without inventive input. For example, a dye, such as a compound of Formula (I) or Formula (II), may comprise about 1% to about 15% by weight of the dye/host composition, for example from about 1% to about 10%; about 1% to about 7.5%; about 1% to about 5%; about 1% to about 3%; about 3% to about 7%; about 2.5% to about 5%; about 4% to about 6%; or about 1%, 2%, 3%, 4% or 5% by weight.

[00137] In some examples, a dye/host composition, particularly as a coating or thin film, comprises l-5wt% Cibalackrot A or Cibalackrot B in mCP:HBT mixed host (4:1 by weight). In a particular example, the composition comprises about 2wt% Cibalackrot B in mCP:HBT mixed host (4:1 by weight). In some examples the host is F8BT [poly(9,9-dioctylfluorene-alt-benzothiadiazole)]. The dye:host composition is suitably formulated in a solvent to enable formation of a film or coating by deposition from the solvent. Those skilled in the art will readily be able to determine a suitable solvent or solvent system depending on the selection of the particular dye, host and application. In some embodiments, a solvent is chloroform.

Methods of Synthesis

[00138] The dye compounds of the present invention are bay-annulated derivatives of indigo and are commonly known as Cibalackrots. Compounds of Formula (I) and the dimers of Formula (II) may be prepared by conventional multistep synthetic routes known in the art. General synthetic routes are described below. Unless otherwise indicated, variables have the meanings as previously defined above. These general synthetic routes can be adapted to prepare compounds of the invention. The preparation of specific compounds is described in the Examples below.

[00139] The compounds of the present invention are synthesised through a series of annulation reactions. The core tetracycle of the compounds can be synthesized through a series of annulation reactions using indigo, or derivatives thereof, and the appropriate reagent

[00140] The present inventors have found that the compounds of Formula (I) may be synthesized by reacting an acid chloride (a phenylacetic acid chloride) with a derivative of indigo. The synthetic route may be a stepwise route, or a "one-pot" synthesis as illustrated below. Route A is a one-pot reaction, while route B is a stepwise synthesis. wherein , R ¹ , R ² , x and y are as herein defined for compounds of Formula (I) and

(II).

[00141] This double annulation reaction of the acid chloride with indigo can be achieved by heating the reactants at reflux in xylene for about three days. Yields of 5- 20% after purification are typical.

[00142] The present invention also provides a process for preparing a compound of Formula (I) comprising reacting an acid chloride with indigo or an indigo derivative.

[00143] The identity of the substituents R ¹ and their location are determined by the substitution on the acid chloride used in the annulation reaction. The identity of the substituents R ² and their location are determined by the substitution on the indigo used in the coupling reaction. One skilled in the art would understand that a wide variety of substitution patterns around the compound of Formula (I) can be accessed by judicious choice of the acid chloride and the indigo derivative under appropriate conditions.

[00144] The choice of acid chloride will depend on the desired R ¹ substituent(s). Acid chlorides, also known as acyl chlorides, may be available from commercial sources, or may be synthesized using routes well known to those skilled in the art. Preferably, the acyl chloride is generated in situ. For example, an acid chloride may be prepared by reacting the corresponding carboxylic acid with thionyl chloride, phosphorus trichloride or phosphorus pentachloride under suitable reaction conditions. In some examples, the carboxylic acid is converted to the acyl chloride by heating at about 85 °C in an inert atmosphere for about 16 hours.

[00145] Carboxylic acids, such as the substituted phenyl acetic acids used herein as precursors to acyl chlorides, may be obtained from commercial sources. Alternatively, the required phenyl acetic acid may be synthesized using known methodology from the appropriate commercially available starting materials. Synthetic routes for the preparation of ring-substituted phenyl acetic acids are well known in the art.. Phenyl acetic acids wherein R ¹ is an alkyl group may be prepared from an appropriate bromophenylacetic acid using known methods of functional group transformations. For example, 4-bromophenylacetic acid may be protected as an ester by reacting the acid with an alcohol, e.g. methanol, under acidic conditions. A subsequent palladium catalyzed Suzuki coupling of the resulting ester with the appropriate 9-alkyl-9- borabicyclo[3.3. l]nonane under mild conditions followed by deprotection of the resulting ester using LiOH provides the phenylacetic acid. 9-Alkyl substituted 9-BBN reagents, such as 9-dodecyl-9-borabicyclo[3.3.1]nonane, may be prepared according to well- known methods from the corresponding alkene (e.g., 1-dodecene) and 9- borabicyclo[3.3.1]nonane (9-BBN) (N. Miyamura, et al., J. Am. Chem. Soc., 1989, 111, 314).

[00146] Alkoxy-substituted phenylacetic acids (i.e., R ¹ is alkoxy) may be commercially available, or can be synthesized using known methodology, such as described in the Examples herein. For example, the required alkoxyphenylacetic acid may be synthesized using a Williamson ether synthesis from the appropriate alkyl bromide and hydroxyphenyl acetic acid, e.g. 2-(4-hydroxyphenyl)acetic, in the presence of potassium hydroxide. [00147] Indigo and indigo derivatives where R ² is halogen or aryl may be available commercially, or can be prepared using known literature methods or methods analogous to known methods.

[00148] For example, 5,5'-dihaloindigo and 5,5'-diphenyl indigo compounds are known (V. Klimovich, et al, J. Mater. Chem. C, 2014, 2, 7621,; O. Pitayatanakul et ah, Engineering Journal, 2015, 19(3).

[00149] 6,6'-Dibromoindigo 6,6-Dibromoindigo may be prepared using the route described in J. L. Wolk, et al, Molecules, 2010, 15 5561.

[00150] Substituted indigo compounds may also be prepared using well known methodology as illustrated below. Indigo derivatives may be prepared from appropriately substituted indoxyls or indoxyl-2-carboxylic acids. Alternatively, indigo compounds may be prepared from the corresponding nitrobenzaldehyde or acetylindolyl acetate starting material.

[00151] Indoxy-2-carboxylic acids and indoxyls may be prepared from the respective phenylglycine-o-carboxylic acid or phenyl glycine, respectively. Nitrobenzaldehydes and acetylindolyl acetates are commercially available, or may be prepared using known methodology.

[00152] The compounds of Formula (II) are dimers of compounds of Formula

(I) joined together by a linker. Preparation of compounds of Formula (II) is achieved by the coupling of compounds of Formula (I) bearing the appropriate functional groups with the desired linker under appropriate conditions.

[00153] The present inventors have found that compounds of Formula (I) where at least one instance of R ¹ is a halogen, preferably one instance of halogen, allows for the compound of Formula (I) to be dimerised with an appropriate coupling partner. Examples of suitable compounds of Formula (I) have the structure of Formula (Ic): where one instance of R ¹ represents chlorine, bromine or iodine (i.e. a halogen), and the other instance of R ¹ and x are as defined above.

[00154] Accordingly, in some embodiments of the compound of Formula (I), each instance of R ¹ is different, such as in compounds of Formula (Ic). In some embodiments of the compound of Formula (Ic), one instance of R ¹ is a halogen and the other instance of R ¹ is a C3-C30 alkyl group. In another embodiment, of the compound of Formula (Ic), one instance of R ¹ is iodine and the other instance of R ¹ is a C3-C30 alkyl group.

[00155] One skilled in the art would understand that preparation of compounds of Formula (Ic) differ from the synthesis described above, since each instance of R ¹ is different. Accordingly, two different acid chlorides are required for the annulation reaction with the indigo derivative. The nature of the substituents on the acid chloride are determined by the substituents intended for the compound of Formula (Ic).

[00156] The compound of Formula (Ic) bearing a halogen functional group contains an aryl or heteroaryl halide functionality, which may be coupled with a linker bearing two instances of an appropriate functional group. The present inventors have found that the aryl or heteroaryl halide of Formula (Ic) can undergo a palladium-catalysed cross -coupling reaction with a linker bearing an appropriate boron-containing functional group. Examples of boron-containing functional groups that may be appropriate include boronic acids and boronate esters, such as pinacol boronic esters.

[00157] In producing a compound of Formula (II), two equivalents of the compound of Formula (Ic) is required for every equivalent of the linker.

[00158] Certain substituents in any of the reaction intermediates or compounds of Formula (I) or (II) may be converted to other substituents by conventional methods known to those skilled in the art. For example a substituent R ¹ may be converted to another substituent R ¹ ; or a substituent R ² may be converted to a different R ² substituent. Such transformations are well known in the art and are described in, for example, Richard Larock, Comprehensive Organic Transformations, 2 ^nd Edition, Wiley, ISBN 0-417- 19031-4.

[00159] It will be appreciated that it may be necessary to protect certain substituents during one or more of the above procedures. Those skilled in the art will recognize when a protecting group is required. Standard protection and deprotection techniques, such as those described in Peter G.M. Wuts, Greene's Protective Groups in Organic Synthesis, Wiley, New York, 2014 ISBN 9781118057483, may be used. It will be appreciated that protecting groups may be interconverted using conventional means.

[00160] The reactions and processes described herein may employ conventional laboratory techniques for heating and cooling, such as thermostatically controlled oil baths or heating blocks and ice baths or solid C0 ₂ /acetone baths. Use of inert atmospheric conditions such as nitrogen or argon may be employed. Conventional methods of isolation of the desired compound, such as extraction or precipitation techniques, and the like, may be used. Organic solvents or solutions may be dried where required using standard, well-known techniques. Purification of compounds or intermediates may be effected using conventional techniques such as chromatography and/or crystallisation.

Methods of Use

[00161] The dye compounds of Formula (I) and Formula (II) find application as deep-red organic dyes. They are solution processable, facilitating preparation of coatings and films, such as thin films. In use, dyes of Formula (I) or (II) have been shown to exhibit good PFQYs and low ASE thresholds (for example, 9.6 pJ cm ² ). Deep-red emission peaked at 650 nm when blended in a mixed host matrix of, for example, 1,3- bis(7V-carbazolyl (benzene (mCP) and 2-hydroxyphenylbenzothiazole (HBT) or mCP and bcnzo[d]thiazol-2-yl)-5-(9//-carbazol-9-yl (phenol (HBT-Cz),. In contrast to a single blend in mCP host, the co-blend films were found to significantly enhance the photostability by retaining 90% of initial ASE intensity even after continuous pumping with over 9,000 pulses at a pump input energy twice that of the ASE threshold. Low lasing threshold of 6 pJ cm ² was further achieved at 641 nmby using distributed feedback gratings. Transient absorption spectroscopy measurements indicated that the dye compounds have extremely low yield of triplet excited-state under optical excitation. [00162] In particular, the deep-red dye compounds of Formula (I) or Formula (II) as defined herein find potential utility in organic solid-state lasers; opto-electronic applications; laser diodes; light-emitting diodes; solar cells; sensors; and photorefracdve devices.

[00163] These dye compounds can be used to amplify in the deep-red region of the spectrum. This property finds utility in fields such as data communication and metal- organic plasmonic devices and, potentially, electrically pumped organic lasers. In particular, the dyes find application as an active gain medium for light amplification in organic solid-state lasers.

[00164] In some embodiment, the dye compounds are useful in laser technology as semiconductor laser dyes and may be used in accordance with methods and apparatus well known to those in the art.

[00165] In some embodiments, a dye compound of Formula (I) or Formula (II) can be used as an active gain medium for light amplification. In particular, the dyes may find application as an organic semiconductor active gain medium for light amplification in organic solid-state lasers (OSSLs) (see, P. P. Sorokin etal., IBM J. Res. Dev. 1966, 10, 162; M. D. McGehee, etal., Adv. Mater. 2000, 12, 1655; A. J. Kuehne, etal., Chem. Rev. 2016, 116, 12823).

[00166] OSSLs have potential as a new light source for applications in fields such as spectroscopy (see, e.g. X. Liu, etal. Opt. Express, 2013, 21, 28941), chemical/bio sensing (see, e.g. Y. Wang, et ah, Laser Photononics Rev. 2013, 7, L71 and optical data communications (see, e.g. J. Clark, et al., Nat. Photonics 2010, 4, 438).

[00167] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications which fall within the spirit and scope.

[00168] In order that the invention may be readily understood and put into practical effect, particular preferred embodiments will now be described by way of the following non-limiting examples. EXAMPLES

General

[00169] All commercial reagents and starting materials were used as received unless otherwise stated.

Synthesis and Characterisation

[00170] Tetrahydrofuran (THF) and dimethylformamide (DMF) were dried using a solvent purification system (LC SPBT-1 Bench Top) before use. Anhydrous xylene and 1,4-dioxane were prepared by drying over activated 4 A molecular sieves. Petroleum with boiling points in the range of 40-60 °C, and dichloromethane (DCM) were distilled prior to use for column chromatography, using Merck LC60A 40-30 silica gel. Solvent ratio used for column chromatography is reported by volume.

[00171] Microwave reactions were performed in crimp-capped, sealed glass vials in a CEM Discover ^® S Microwave Synthesizer. The wattage was automatically adjusted to maintain the desired temperature for the desired period of time.

[00172] All NMR spectra were recorded using Bruker Avance 300 or 500 MHz spectrometers in CDCb. All chemical shifts (d) were reported in parts per million (ppm) and referenced to the residual CDCI3 solvent peak at d 7.26 ppm and 77 ppm for ¹ H and ¹³ C NMR, respectively. Multiplicities were reported as singlet (s), doublet (d), triplet (t), multiplet (m), doublet of doublets (dd) and doublet of triplets (dt); and dtd (doublet triplet doublet); Ph-H = phenyl H, Fur-H = furanyl H, Cbk-H = Cibalackrot H and Ind-H Indigo H. All coupling constants (J) were quoted in Hertz (Hz) and rounded to the nearest 0.5 Hz.

[00173] Melting point (m.p.) was measured in a glass capillary on a Buchi Melting Point B-545 and was uncorrected. Infrared spectra were recorded on a Perkin Elmer Spectrum 1000 FT-IR spectrometer with ATR attachment as solid state. Mass spectrometry was performed on either an Applied Biosystems Voyager MALDI-TOF MS using a 2,5-dihydroxy benzoic acid (TA) matrix or a Bruker Esquire HCT (High Capacity 3D ion trap) electrospray ionization (ESI) MS or a Bruker MicrOTof-Q for the accurate mass in ESI mode. Absorption spectra were recorded on a Varian Cary 5000 UV-Vis- NIR spectrophotometer in 10 x 10 mm quartz cuvettes and k _a|1 values are quoted in nm with shoulders denoted as "sh". [00174] The thermal gravimetric analysis (TGA) measurement was performed on a Perkin Elmer STA 6000 under 20 °C min ¹ under an inert atmosphere, the TGA temperature was quoted at 5% weight loss as the decomposition temperature. Differential scanning calorimetry (DSC) was used to investigate thermal properties with heating and cooling rates of 200 °C min ¹ under a nitrogen atmosphere. Infrared spectra were collected on a Perkin Elmer Spectrum 1000 FT-IR in neat form. Mass spectra were obtained on either the BRUKER MicrOTof-Q with the DIONEX UltiMate 3000 LC, or the Thermo Orbitrap Elite with ETD with Dionex UltiMate 3000 RSLCnano.

Electrochemical measurements

[00175] Electrochemistry was conducted using an Epsilon C3 BAS electrochemistry station using glassy carbon working, 0.1 M AgN0 ₃ in acetonitrile reference, and platinum counter electrodes. All measurements were conducted at room temperature with the sample concentration of 1 mM in dichloromethane (distilled from calcium hydride) and 0.1 M tctra-n-butyl am moni um perchlorate as the electrolyte. The solution was deoxygenated with argon and a ferricenium/ferrocene (Fc ⁺ /Fc) couple was used as standard. The scan rate was 100 mV s ¹ .

Photophysical measurements

[00176] UV-visible absorption spectra were measured using a Cary-5000 UV- Vis spectrophotometer for thin films and solutions. PL spectra were obtained using Horiba Jobin Yvon Fluoromax. Solution PLQYs were determined using Rhodamine 6G (PLQY = 98%) in ethanol as the standard (D. Magde et ah, Photochem. Photobiol. 2002, 75, 327). Optical density of sample and standard were fixed at -0.1 at excitation wavelength of 500 nm. Solid-state PLQY measurements were performed using a calibrated integrating sphere (N. C. Greenham et al., Chem. Phys. Lett. 1995, 241 , 89). Nano-second transient absorption spectroscopy (TAS) were performed with an EOS transient absorption spectrometer (ultrafast system, LLC). Amplified laser system (spitfire ACE, spectra physics) delivering -100 fs laser pulses at 800 nm with repetition rate of 1 kHz was coupled to optical parametric amplifier (TOPAS) to generate 'pump' beam excitation at 525 nm. A pulsed Nd:YAG based Leukos-STM super continuum light source was used to generate white light continuum ‘probe’ (ca. 380-900 nm). The timing of the probe pulse was controlled electronically using the sync out of the amplified laser system. Solid-state TCSPC measurements were performed using Halcyone fluorescence spectrometer with instrument response of 150 picoseconds (ps); samples were excited at 337 nm using amplified laser system as described for TAS measurements. Emission was monitored at 592 nm for Cibalackrot A and 605 nm for Cibalackrot B. Solution TCSPC measurements were performed on a Jobin-Yvon Fluorolog 3 with excitation at 372 nm from pulsed NanoLED source (Horiba).

Thin film preparation

[00177] Thin films for photophysical and ASE measurements were prepared using same procedure. Thin films were spin coated from 20 mg mL ¹ chloroform solutions at 1,500 rpm on fused silica substrates to obtain thickness of 140-150 nm. The substrates were cleaned with acetone and isopropanol followed by UV-ozone to remove organic impurity before spin coating. For thickness dependence of ASE, chloroform solutions with concentrations of 25-30 mg mL ¹ were used and spin speeds were varied to obtain thickness variation. Freshly distilled chloroform was used in all the measurements.

ASE measurements

[00178] ASE properties were determined by optically exciting the samples at excitation wavelength of 337 nm with a 3.5 ns pulse using randomly polarised nitrogen- gas laser (Stanford Instruments, NL-100) operating at 20 Hz frequency. The laser beam was focused on a 0.5 x 0.01 cm ² area using cylindrical lens and the edge of the laser beam was cut using slit to obtain uniform spot size. Excitation intensity was controlled using neutral density filters. To prevent degradation, samples were kept in a quartz chamber under vacuum (10 ⁶ torr). Output from the edge of the sample was collected using an optical fibre and spectrometer (Hamamatsu, Mini-spectrometer TM series, C10083CA) with optical resolution of 5 nm.

DFB fabrication and measurements

[00179] The DFB gratings used for optically pumped laser studies were manufactured on 0.5 mm thick Si wafers with 2 pm layer Si0 ₂ (SWI). The substrates were first cleaned with ultrasonic bath in IPA and acetone (10 minutes each), followed by oxygen plasma cleaning (5 minutes at 50 W). The resist used was PMMA 950K A4 (MicroChem), which was spin-coated at 4,000 rpm for 60 s, followed by 10 minutes soft bake on a hotplate at 185 °C. 200 nm period gratings were patterned using EBPG5150 system (Raith) with the operating voltage of 100 kV and dose of 1200 uC cm ² on area of 2 x 2 mm ² . After patterning, the substrates were developed in 1:3 MIBK:IPA mixture for 60 s, rinsed with IPA and dried with nitrogen. Obtained gratings were imaged using E- Line SEM (Raith) in SE mode with 10 kV accelerating voltage and 30 pm aperture. Refractive index and extinction coefficients were determined using variable angle spectroscopic ellipsometry (VASE) (J.A. Wollam, VUV) on 150 nm thick film of 2wt% Cibalackrot derivative blended in the mixed host. Analytical software (WVASE) was then used to analyse the ellipsometry data. DFB laser studies were performed using similar setup as discussed above for ASE studies, though the length of the excitation beam was reduced to 2 mm so as to excite just the DFB pattered area of the substrate. Emission from the samples were collected from the edge of the sample using an optical fibre and spectrometer (Thor labs, CCS 100) with optical resolution of 0.5-1 nm. Reproducibility and error in all measurements was confirmed by testing at least three different samples.

General Synthetic Procedure for Compounds of Formula (I):

Synthesis of acid chloride

[00180] A mixture of the desired carboxylic acid (1 e.q.) and thionyl chloride (4 e.q.) was heated in an 85 °C oil bath under argon for 2 h. The reaction was then allowed to cool to room temperature ,and the excess thionyl chloride was removed in vacuum to give the desired acid chloride (-100%) which was used without further purification.

Synthesis of Cibalackrot Compound of Formula (I): Cibalackrots

[00181] Indigo (1 e.q.) was added to a solution of acid chloride (24 e.q.) in xylene (0.15 M). The mixture was heated in an 160 °C oil bath under argon for 3 days. The reaction mixture was allowed to cool to room temperature and diluted with diethyl ether (30 mL). The resulting precipitate was collected by filtration. The red solid mixture was purified by column chromatography over silica using dichloromethane/petroleum (0:1 to 1:1) as eluent to give the desired Cibalackrot.

General Synthetic Procedure for Compounds of Formula (II): Cibalackrot Dimers

[00182] A mixture of phenylacetic acid (1 e.q.) and the thionyl chloride (4 e.q.) was heated in an 80 °C oil bath under a flow of N2 for 3 h. The reaction was then allowed to cool to room temperature. The excess thionyl chloride was removed in vacuum to give the desired phenylacetyl chloride (-100%) which was used without further purification. [00183] A mixture of indigo (1 e.q.), and magnesium sulphate (12 e.q.) in dry 1,4-dioxane (0.03M) is heated to reflux in a 115 °C oil bath under argon phenylacetyl chloride (3 e.q.) was then added dropwise, followed by slow portion-wise addition of potassium ieri-butoxide (4 e.q.). The resulting mixture was allowed to stir for 30 minutes. The mixture was then cooled to room temperature and quenched with water (30 mL), and the resulting precipitate was collected by filtration and washed with methanol until the filtrate is clear. The dark pink solid is purified by trituration with methanol, and n-hcxanc then taken up in a dichloromethane/ ethyl acetate solvent mixture and pulled through a short plug of celite. The solvent is the removed to give the desired mono-Cibalackrot precursor.

[00184] A mixture of 4-iodophenylacetic acid (1 e.q.) and thionyl chloride (4.5 e.q.) was heated in an 80 °C oil bath under argon for 2 h. The reaction is then allowed to cool to room temperature. The excess thionyl chloride is removed in vacuum to give 4- iodophenylacetyl chloride (-100%) which is used without further purification.

[00185] A mixture of mono-Cibalackrot (1 e.q.), and 4-iodophenylacetyl chloride (11 e.q.) in -xylcnc (0.1 M) was heated in an 145 °C oil bath under a flow of N2 for 18 h. The reaction was allowed to cool and diluted with n-hexane (-30 mL) and the resulting precipitate was collected by filtration and washed with methanol, n-hexane, and diethyl ether until filtrate was clear. The red solid was taken up in chloroform and pulled through a short plug of silica, followed by further trituration with methanol, and n-hexane to give a bright red powder of cibalckrot monomer.

[00186] A mixture of boronic ester (1 e.q.), Cibalackrot monomer (2.4 e.q.), tetrabutylammonium bromide [TBAB] (2 e.q.), and 2 M K2CO3 (5 e.q.), in toluene (0.04M) was sparged with N2 for 20 mins while stirring. Pd(PPh3)4 (0.15 e.q.) was then added under argon, and the mixture was sparged with N2 for 10 mins. The reaction was then heated in a 110 °C oil bath for 16h. The mixture was then allowed to cool to room temperature and diluted with chloroform (15 mL) and washed with water (20 mL), saturated sodium carbonate solution (20 mL), brine (20 mL), dried over anhydrous MgSCL and filtered through a short plug of celite. The solvent is removed to give a red solid which was purified by column chromatography over silica neutralised with triethylamine (2%). Example 1

Preparation of 7,14-bis(4-dodecylphenyl)diindolo[3,2,l-de:3',2',r- ij][l,5]naphthyridine-6,13-dione, Cibalackrot A

Preparation of methyl (4-bromophenyl) acetate, 1:

[00187] A mixture of 4-bromophenylacetic acid (2.08 g, 9.66 mmol), sulphuric acid (-0.5 mL) in methanol (15 mL) was reacted in a microwave reactor for 1 minute irradiated to 80 °C at 150 W using the PowerMAX setting. The reaction was allowed to cool, then quenched with saturated sodium carbonate solution until neutral. The white mixture was extracted with diethyl ether (3 x 50 mL) and the combined extracts were washed with water (100 mL), saturated sodium carbonate solution (100 mL), brine (100 mL), then dried over anhydrous sodium sulphate and filtered. The filtrate was then collected and solvent was removed to give 1 as a clear oil (2.19 g, 99%); ^X H NMR (300 MHz, CDCb): d 3.58 (2 H, s, COCH ₂ ), 3.70 (3 H, s, OCH ), 7.16 & 7.46 (4 H, AA’XX’, Ph-H); ¹³ C NMR (75 MHz, CDCb): d 40.5, 52.1, 121.2, 131.0, 131.7, 132.9, 171.4; which were identical to reported results.

Preparation of methyl 2-(4-dodecylphenyl) acetate, 2:

R = n-dodecyl

[00188] A solution of 9-borabicyclo[3.3.1]nonane (9-BBN, 0.5 M in THF, 75 mL, 37.5 mmol) was added slowly to a stirring solution of 1-decene (6.07 g, 36.1 mmol) in dry THF (7 ml) at 0-2 °C (in an ice bath). The reaction mixture was deoxygenated by placement under vacuum and back filling with argon three times, warmed to room temperature, and stirred under argon for 5 h. [1,1'-

Bis(diphenylphosphino)ferrocene]dichloropalladium(II) (845 mg, 1.15 mmol), potassium carbonate (11.5 g, 83.2 mmol) and 1 (7.08 g, 30.9 mmol) in dry DMF (100 mL) were added to the mixture. The reaction was deoxygenated once again and heated in a 50 °C oil bath under argon for 22 h. The reaction mixture was allowed to cool to room temperature and water was added (100 mL). The mixture was extracted with diethyl ether (4 x 100 mL). The ether extracts were combined and washed with water (100 mL) and brine (100 mL). The organic layer was dried over anhydrous sodium sulphate and filtered. The filtrate was collected and the solvent removed. The mixture was purified by column chromatography over silica using dichloromethane and ethyl acetate-light petroleum (0: 1 to 1:3) as eluent to give 2 as a colourless oil (9.07 g, 92%); „, _ax (CH ₂ Cl ₂ )/nm: 225 (e/dm ³ mol ¹ cm ¹ 24,816); V _max ineatVcrn ¹ 1741 (vs, C=0); NMR (500 MHz, CDCh): d 0.89 (3 H, t, / = 7.0, CH ), 1.23-1.36 (18 H, m, CH ₂ ), 1.60 (2 H, q, / = 7.5, CH ₂ ), 2.59 (2 H, t, /= 8.0, CH ₂ ), 3.60 (2 H, s, COCH ₂ ), 3.69 (3 H, s, OCH ₃ ), 7.13-7.20 (4 H, AA'XX', Ph- H); ¹³ C NMR (125 MHz, CDC1 ): d 14.1, 22.7, 29.3, 29.5, 29.6, 29.6, 29.7, 31.4, 31.9, 35.6, 40.8, 51.9, 128.6, 129.0, 131.1, 141.8, 172.2; m/z [ES ⁺ ] 319.3 [M+H] ⁺ ; 341.2 [M+Na] ⁺ .

Preparation of 2-(4-dodecylphenyl) acetic acid, 3:

R = n-dodecyl

[00189] A mixture of 2 (1.92 g, 6.04 mmol), lithium hydroxide (840 mg, 35 mmol), methanol (8 mL), deionised water (8 mL) and tetrahydrofuran (28 mL) was heated in a 65 °C oil bath under argon for 18 h. The mixture was allowed to cool to room temperature, and the solvent was removed under reduced pressure. Aqueous hydrochloric acid (3 M, 20 mL) was added to the residue and the mixture was extracted with diethyl ether (3 x 75 mL). The combined ether extracts were washed with water (100 ml), brine (100 mL), and dried over anhydrous sodium sulphate and filtered. The filtrate was collected and solvent removed. The crude was recrystallised from petroleum spirits to give 3 as a white crystal (1.81 g, 99 %); m.p. 91.3-92.5 °C; _max (CH ₂ Cl ₂ )/nrn: 224 (e/dm ³ mol ¹ cm ¹ 24,397); V _max ineatycrn ¹ 3023 (br; OH), 1680 (vs, C=0); ^l U NMR (300 MHz, CDC1 ): d 0.90 (3 H, t, J = 7.0, CH ), 1.22-1.38 (18 H, m, CH ₂ ), 1.60 (2 H, q, J = 8.0, CH ₂ ), 2.59 d(2 H, t, /= 8.0, PhCH ₂ ), 3.62 (2 H, s, COCH ₂ ), 7.13-7.21(4 H, AA'XX', Ph- H); ¹³ C NMR (75 MHz, CDC1 ): d 14.1, 22.7, 29.3, 29.5, 29.6, 29.6, 29.7, 31.4, 31.9, 35.6, 40.6, 128.7, 129.2, 130.4, 142.1, 178.0; m/z [ES ⁺ ] 327.2 [M+Na] ⁺ ; 341.2 [M+K] ⁺ . 7,14-Bis(4-dodecylphenyl)diindolo[3,2,l-de:3',2',l'-ij][l,5] naphthyridine-6,13- dione, Cibalackrot A:

[00190] A mixture of 3 (1.12 g, 3.68 mmol) and thionyl chloride (3.0 mL, 41.1 mmol) was heated in an 85 °C oil bath under argon for 16 h. The reaction was allowed to cool to room temperature. The excess thionyl chloride was removed in vacuum to leave brown/orange oil, which solidified at room temperature as 5 (-1.10 g, -93%), which was used without further purification. Indigo (161 mg, 0.62 mmol) was added to a solution of 5 (~ 1.10 g, -3.41 mmol) in xylene (10 mL). The mixture was heated in at 160 °C in an oil bath under argon for 3 days. The reaction mixture was allowed to cool to room temperature and diluted with diethyl ether (30 mL). The resulting precipitate was collected by filtration. The red solid mixture was purified by column chromatography over silica using dichloromethane/light petroleum (0:1 to 1:3 to 1:1) as eluent to give Cibalackrot A as an orange solid (35.2 mg, 7%); m.p. -306.2-309.6 °C; k _max (CH ₂ Cl ₂ )/nm: 277 (e/dm ³ mol ¹ cm 55,142), 508 sh (26,761), 544 (37,340); v _max (neat)/cm ^_1 1627 (vs, C=0); ^l U NMR (500 MHz, CDCh): d 0.88 (6 H, t, / = 7.0, CH ), 1.21-1.45 (36 H, m, CH ₂ ), 1.70 (4 H, q, / = 7.5, CH ₂ ), 2.73 (4 H, t, /= 8.0, PhCH ₂ ), 7.22 (2 H, td, J = 1.5 & 1.0, Cbk-H), 7.39 (4 H, 1/2AA'XX', Ph-H), 7.55 (2 H, td, / =1.0 & 8.5, Cbk-H), 1.63-1.61 (6 H, m, Ph-H & Cbk-H), 8.51 (2 H, d, /= 8.0, Cbk-H); ¹³ C NMR (75 MHz, CDCls): d 14.1, 22.7, 29.4, 29.4, 29.6, 29.6, 29.7, 29.7, 31.4, 31.9, 36.0, 117.6, 122.1, 125.5, 125.8, 125.9, 127.0, 128.6, 130.0, 130.7, 131.3, 131.8, 132.0, 144.3, 144.6, 159.6; m/z [ES ⁺ ] 799.5 [M+H] ⁺ . C ₅₆ H ₆₆ N ₂ 0 ₄ requires: C, 84.2; H, 8.3; N, 3.5; found: C, 83.8; H, 8.3; N, 3.5.

EXAMPLE 2

Preparation of 7,14-bis(4-((2-ethylhexyl)oxy)phenyl)diindolo[3,2,l-de:3',2' ,l'- ij][l,5]naphthyridine-6,13-dione, Cibalackrot B: Preparation of 2-(4-((2-ethylhexyl)oxy)phenyl)acetic acid, 4:

R = 2-ethylhexyloxy

[00191] A mixture of 2-(4-hydroxyphenyl)acetic acid (10.0 g, 65.9 mmol), 2- ethylhexyl bromide (13.0 mL, 80.8 mmol), potassium hydroxide (14.8 g, 264 mmol) and dimethyl sulfoxide (150 mL) was heated in a 70 °C oil bath under argon for 17 h. The mixture was allowed to cool to room temperature before being added with aqueous HC1 (3 M, 100 mL). The mixture was extracted with dichloromethane (3 x 250 mL). The dichloromethane extracts were combined, washed with brine (2 x 100 mL), dried over anhydrous sodium sulfate and filtered. The filtrate was collected and the solvent was removed. The residual was purified by column chromatography over silica using ethyl acetate/light petroleum (1:4) as eluent to give 4 as colourless oil (11.7 g, 67%); ¹ H NMR (300 MHz, CDCb): d 0.88-0.95 (6 H, m, CH ), 1.25-1.55 (8 H, m, CH ₂ ), 1.65-1.75 (1 H, m, CH), 3.59 (1 H, s, CH), 3.82 (2 H, d, / = 5.5, OCH ₂ ), 6.87 (2 H, 1/2AA'XX', Ph- H), 7.19 (2 H, 1/2AA'XX', Ph-H); ¹³ C NMR (75 MHz, CDCb): d 11.2, 14.2, 23.2, 24.0, 29.2, 30.6, 39.5, 40.2, 70.6, 114.8, 125.1, 130.5, 158.9, 177.4.

7,14-Bis(4-((2-ethylhexyl)oxy)phenyl)diindolo[3,2,l-de:3' ,2',r- ij][l,5]naphthyridine-6,13-dione, Cibalackrot B:

[00192] A mixture of 4 (9.50 g, 35.9 mmol) and thionyl chloride (26 mL, 358 mmol) was heated in a 78 °C oil bath under argon for 15 h. The mixture was allowed to cool to room temperature, and excess thionyl chloride was removed in vacuo to give brown oil. This was directly used for next step (~90%). A mixture of the brown oil (9.10 g), indigo (400 mg, 1.53 mmol) and xylene (100 mL) was heated in a 160 °C oil bath under argon for 3 days. The mixture was allowed to cool to room temperature, and diethyl ether (300 mL) was added and red precipitates were formed. The mixture was filtered, and the red precipitates were collected and washed with diethyl ether (100 mL). The red solid was purified by column chromatography over silica using dichloromethane as eluent to give Cibalackrot B as a red solid (198 mg, 18%); m.p. >385 °C; k _max (CH ₂ Cl ₂ )/nm 280 (e/dm ³ mol ¹ cm ¹ 51,286), 518 (29,512), 554 (39,811); V _max ineatycm ¹ : 1625 (s, C=0); 1.00 (12 H, m, CH ), 1.35-1.54 (16 H, m, CH ₂ ), 1.76-1.85 (2 H, m, CH), 3.96-3.98 (4 H, m, OCH ₂ ), 7.09 (4 H, 1/2AA'XX', Ph-H), 7.20- 7.25 (2 H, m, Cbk-H), 7.52-7.56 (2 H, m, Cbk-H), 7.66-7.70 (6 H, m, Cbk-H, Ph-H), 8.50 (2 H, d, /= 8.0, Cbk-H). ¹³ C NMR (100 MHz, CDCb): d 11.2, 14.1, 23.1, 23.9, 29.1, 30.6, 39.4, 70.6, 114.5, 117.6, 121.9, 125.4, 125.4, 125.9, 130.8, 131.6, 131.8, 144.5, 159.7, 160.2; m/z [MALDI-TOF, AT]: Anal. Cal. for C ₄₈ H ₅ oN ₂ 0 ₄ : 718.4 (100%), 719.4 (32%), 720.4 (3%). Found [M+H]: 719.3 (100%), 720.3 (40%), 721.3 (8%). C ₄₈ H ₅₀ N ₂ O ₄ requires: C, 80.2; H, 7.0; N, 3.9; found: C, 80.0; H, 7.0; N, 3.9.

Example 3

Preparation of 14,14'-((9,9-dihexyl-9H-fluorene-2,7-diyl)bis(4,l-phenylene) )bis(7- (4-((2-ethylhexyl)oxy)phenyl)diindolo[3,2,l-de:3',2',r-ij][l ,5]naphthyridine-6,13- dione), Cibalackrot Dimer C:

Preparation of 7-(4-((2-ethylhexyl)oxy)phenyl)-6H-pyrido[l,2-a:3,4-b']diind ole- 6,13(12H)-dione, 5:

[00193] A mixture of indigo (152 mg, 0.58 mmol, 1 e.q.), and magnesium sulphate (1 g, 7.2 mmol, 12 e.q.) in dry 1,4-dioxane (19 mL, 0.01M) is heated to reflux in a 115 °C oil bath under argon. 2-(4-((2-ethylhexyl)oxy)phenyl)acetyl chloride, (520 mg, 1.84 mmol, 3 e.q.) was then added dropwise, followed by slow portion-wise addition of potassium tert-butoxide (270 mg, 2.4 mmol, 4 e.q.). The resulting mixture was allowed to stir for 30 minutes. The mixture was then cooled to room temperature and quenched with water (30 mL), and the resulting precipitate was collected by filtration and washed with methanol until the filtrate is clear. The dark pink solid is purified by trituration with methanol, then taken up in a dichloromethane/ ethyl acetate solvent mixture and pulled through a short plug of celite. The solvent is the removed to give 5 as a purple solid (130 mg, 46%). Ή NMR (300 MHz, CDCh) d 0.94-1.02 (6 H, m, CH ), 1.36-1.55 (4 H, m, CH ₂ ), 1.82 (1 H, q, CH), 3.98 (2 H, d, / = 6.0, OCH ₂ ), 6.96 (1 H, dtd, J = 7.0, 2.0, Ind- H), 7.11 & 7.56 (4 H, AA'XX', Ph-H), 7.25 (1 H, dt, /= 8.0, 1.0, Ind-H), 7.31-7.37 (2 H, m, Ind-H), 7.45 (1 H, dtd, / = 7.0, 2.0, Ind-H), 7.65 (1 H, dtd, /= 8.0, 2.0, Ind-H), 8.50 (2 H, dddd, / = 8.0, 1.0, Ind-H), 8.92 (1 H, s, Ind-NH).

Preparation of 4-iodophenylacetyl chloride, 6:

[00194] A mixture of 4-iodophenylacetic acid (3 g, 11.5 mmol, 1 e.q.) and thionyl chloride (5 mL, 49 mmol, 4.5 e.q.) was heated in an 80 °C oil bath under argon for 2 h. The reaction is then allowed to cool to room temperature. The excess thionyl chloride is removed in vacuum to give 6 as a dark yellow oil (3.2 g, 100%) which is used without further purification. NMR (300 MHz, CDCb) d 4.11 (2 H, s, CH ₂ ), 7.03 & 7.73(4 H, AA'XX', Ph-H).

Preparation of 7-(4-((2-ethylhexyl)oxy)phenyl)-14-(4-iodophenyl)-diindolo[3 ,2,l- de:3',2',r-ij][l,5]naphthyridine-6,13-dione, 7:

[00195] A mixture of 5 (503 mg, 1 mmol, 1 e.q.), and 6 (3.2 g, 11.4 mmol, 11 e.q.) in p-xylene (10 mL, 0.1 M) was heated in an 145 °C oil bath under a flow of N ₂ for 18h. The reaction was allowed to cool and diluted with «-hexane (~30 mL) and the resulting precipitate was collected by filtration and washed with methanol, n-hexane, and diethyl ether until filtrate was clear. The red solid was taken up in chloroform and pulled through a short plug of silica, followed by further trituration with methanol, and n-hcxanc to give a bright red powder of 7 (633 mg, 86%). ^X H NMR (300 MHz, CDCb) d 0.94-1.02 (6 H, m, CH3), 1.36-1.54 (4 H, m, CH ₂ ), 1.82 (1 H, q, CH), 3.99 (2 H, d, OCH ₂ ), 7.13 (2 H, 1/2AA'XX', Ph-H), 7.24-7.28 (2 H, m, Cbk-H), 7.55-7.756 H, m, Cbk-H, Ph-H), 7.95 (2 H, 1/2AA'XX', Ph-H), 8.50 (2 H, d, / = 8.0, 2.0, Cbk-H).

Preparation of 14,14'-((9,9-dihexyl-9H-fluorene-2,7-diyl)bis(4,l-phenylene) )bis(7- (4-((2-ethylhexyl)oxy)phenyl)diindolo[3,2,l-de:3',2',r-ij][l ,5]naphthyridine-6,13- dione), Cibalackrot Dimer C:

[00196] A mixture of 9,9’-dihexylfluorene-2,7-bis(boronic acid pinacol ester (20 mg, 0.034 mmol), 7 (58.5 mg, 0.082 mmol), tetrabutylammonium bromide [TBAB] (22.5 mg, 0.070), 2 M K2CO3 (0.1 mL, 0.2 mmol), in toluene (0.9 mL) was sparged with N2 for 20 mins while stirring. Pd(PPh ₃ )4 (6.2 mg, 0.005 mmol) was then added under argon, and the mixture was sparged with N2 for 10 mins. The reaction was then heated in a 110 °C oil bath for 3 d. The mixture was then allowed to cool to room temperature, diluted with chloroform (15 mL), washed with water (20 mL), saturated sodium carbonate solution (20 mL), brine (20 mL), dried over anhydrous MgSCL and filtered through a short plug of celite. The solvent is removed to give a red solid which was purified by column chromatography over silica neutralised with triethylamine (2%) using DCM/Hex/EtOAc (3:1:2), to give the Cibalackrot Dimer C as a red solid (37.3 mg, 0.80 (6 H, t, CH ₃ ), 0.92-1.02 (12 H, m), 1.06- 1.18(2 H, m), 1.25-1.60 (6 H, m), 1.81 (4 H, m), 2.10-2.15(2 H, m), 3.98 (4 H, d, / = 6.0), 7.10-7.13 (4 H, m), 7.56-7.61 (6 H, m), 7.66-7.80 (14 H, m), 7.86-7.93 (10 H, m), 8.50 (4 H, dd, 7 = 8.0, 3.0). EXAMPLE 4

Preparation of 14,14'-([l,l':3',l"-terphenyl]-4,4"-diyl)bis(7-(4-((2- ethylhexyl)oxy)phenyl)diindolo[3,2,l-de:3',2',l'-ij][l,5]nap hthyridine-6,13-dione), Cibalackrot phenyl Dimer D:

A mixture of 1,3-phenyldiboronic acid bis(pinacol) ester (10.4 mg, 0.032 mmol), 7 (53.9 mg, 0.075 mmol), TBAB (20.1 mg, 0.062), 2 M K ₂ CO ₃ (0.1 mL, 0.2 mmol), in toluene (0.8 mL, 0.04M) was sparged with N2 for 20 mins while stirring. Pd(PPh3)4 (5 mg, 0.004 mmol) was then added under argon, and the mixture was sparged with N2 for 10 min. The reaction was then heated in a 110 °C oil bath for 16h. The mixture was then allowed to cool to room temperature and diluted with dichloromethane (20 mL) the precipitate was collected by filtration through a short plug of celite, then dissolved in hot chloroform (50 mL). The solvent was then removed to give the Cibalackrot Dimer D as a dark red solid (29.2 mg, 0.96 (12 H, m, CH ), 1.35-1.49 (12 H, m), 1.78-1.83 (2 H, m), 3.98 (4 H, d, / = 6.0), 7.10-7.12 (4 H, m), 7.55-7.60 (5 H, m), 7.63-7.78 (13 H, m), 7.90 (8 H, AA'XX'), 8.07 (1 H, s), 8.52-8.55 (5 H, m).

EXAMPLE 5

Preparation of 14,14'-((9,9-dihexyl-9H-fluorene-2,7-diyl)bis(4,l-phenylene) )bis(7- (4-(2-octyldodecyl)oxy)phenyl)diindolo[3,2,l-de:3',2',r-ij][ l,5]naphthyridine-6,13- dione), Cibalackrot Dimer E:

7-(4-((2-Octyldodecyl)oxy)phenyl)-6H-pyrido[l,2-a:3,4-b'] diindole-6,13(12H)- dione, 8:

[00197] A mixture of indigo (313 mg, 1.19 mmol), and magnesium sulphate (2.75 g, 19 mmol) in dry 1,4-dioxane (35 mL) is heated to reflux in a 115 °C oil bath under argon. 2-(4-((2-octyldodecyl)oxy)phenyl)acetyl chloride, (1.61 g, 3.56 mmol) was added dropwise, followed by slow portion- wise addition of potassium tert-butoxide (600 mg, 5.35 mmol). The mixture was allowed to stir for 30 minutes. The mixture was then cooled to room temperature and quenched with water (100 mL), and the resulting precipitate was collected by filtration and washed with methanol until the filtrate is clear. The dark pink solid was purified by trituration with methanol, then taken up in a dichloromethane/ethyl acetate solvent mixture, and pulled through a short plug of celite The filtrate was collected and the solvent was removed to give 8 as a purple solid (353 mg, 0.91 (6 H, m, CH ), 1.23-1.53 (32 H, m, CH ₂ ), 1.84 (1 H, p, / = 6.0, CH), 3.94 (2 H, d, / = 6.0, OCH ₂ ), 6.93 (1 H, dtd, / = 7.5, 1.0 & 1.0, Ind-H), 7.08 & 7.54 (4 H, AA'XX', Ph-H), 7.24 (1 H, ttt, /= 8.0 & 1.0, Ind-H), 7.29-7.34 (2 H, m, Ind-H), 7.42 (1 H, dtd, /= 8.0, 1.0 & 1.0, Ind-H), 7.62 (1 H, dqd, 7= 8.0, 1.5 & 1.0, Ind-H), 7.84 (1 H, dq, /= 8.0 & 1.0), 8.69 (1 H, tt, /= 8.0 & 1.0, Ind-H), 9.01 (1 H, s, Ind-NH).

[00198] A mixture of 8 (653 mg, 0.991 mmol), and 2-(4-iodophenyl)acetyl chloride (3.21 g, 11.44 mmol) in p-xylene (14 mL) was heated in a 145 °C oil bath under nitrogen flow for 23 h. The reaction was then allowed to cool, n-hcxanc (50 mL) was added, and the resulting red precipitate was collected on a pad of celite. This was washed with 77-hexane, ethanol, and then diethyl ether until clear, the red solid was then taken up in chloroform, and filtered through the celite. The solvent was removed to give a red residue, which was precipitated with n-hcxanc/dicthyl ether (1:1) from the chloroform solution to give 9 as a bright red solid (845.6 mg, 96.4%); ^X H NMR (300 MHz, CDCL): d 0.88-0.94 (6 H, m, CH ), 1.27-1.50 (32 H, m, CH ₂ ), 1.87 (1 H, p, J = 6.0, CH), 3.98 (2 H, d, J = 6.0, OCH2), 7.12 & 7.70 (4 H, AA’XX’, OPh-H), 7.24-7.26 (2 H, m, Ciba-H), 7.50 & 7.95 (4 H, AA'XX', IPh-H), 7.55-7.63 (4 H, m, Ciba-H), 7.69-7.75 (2 H, m, Ciba- H), 8.52 (2 H, dd, J = 8.0 & 2.5, Ciba-H).

14,14'-((9,9-dihexyl-9H-fluorene-2,7-diyl)bis(4,l-phenyle ne))bis(7-(4-(2- octyldodecyl)oxy)phenyl)diindolo[3,2,l-de:3',2',l'-ij][l,5]n aphthyridine-6,13- dione), Cibalackrot Dimer E::

[00199] A mixture of 9 (180 mg, 0.204 mmol), 2,2'-(9,9-dihexyl-9H-fluorene- 2,7-diyl)bis(4,4,5,5-tetramethyl-l,3,2-dioxaborolane) (52.7 mg, 0.09 mmol), potassium carbonate (250 mg, 1.8 mmol), tetrahydrofuran (4 mL), and water (1.2 mL) was deoxygenated by “freeze-pump-thaw”, and backfilled with argon. This was repeated for three times. PdCl2(dppf)DCM (11.2 mg, 0.014 mmol) was added to the mixture. The mixture was deoxygenated and backfilled with argon. This was repeated three times. The mixture was heated in a 68 °C oil bath for 20 h. This was then allowed to cool, before addition of water (30 mL), the resulting precipitate was extracted with chloroform (3 x 50 mL). The chloroform extracts were combined, washed with brine (100 mL), dried over anhydrous magnesium sulphate and filtered through a short plug of silica. The filtrate was collected and the solvent was removed to give a red/purple solid, which was purified by column chromatography over neutralised silica (0.5% triethylamine), using chloroform/toluene (1:1) and then dichloro methane as eluent. The product was precipitated from toluene to give the Cibalackrot Dimer E as a red solid (127.6 mg, 77%); NMR (500 MHz, CD ₂ C1 ₂ ): d 0.76-0.87 (10 H, m, CH ₂ & CH ), 0.87-0.90 (12 H, m, Ciba), 1.09-1.20 (12 H, m, L1-CH ₂ ), 1.26-1.47 (64 H, m, Ciba- CH ₂ ), 1.87 (2 H, p, J = 6.0, CH), 2.18 (4 H, t, / = 8.0, L1-CH ₂ ), 4.00 (4 H, d, / = 6.0, OCH ₂ ), 7.12 & 7.70 (8 H, AA'XX', Ph-H), 7.24-7.26 (4 H, m, Ciba-H), 7.60 (4 H, td, / = 6.0 & 3.0, Ciba-H), 7.70 (4 H, ½AA'XX', Ph-H), 7.73 (2 H, d, / = 8.0, Ciba-H), 7.78 (2 H, d, / = 8.0, Ciba- H), 7.80-7.82 (4 H, m, Ciba-H), 7.88 & 7.95 (8 H, AA'XX', Ll-H), 7.90 (1 H, s, Ll-H), 7.93 (1 H, s, Ll-H), 8.51 (4 H, t, / = 8.0, Ciba-H).

EXAMPLE 6

Preparation of 14,14'-([l,l':3',l"-terphenyl]-4,4"-diyl)bis(7-(4-(2- octyldodecyl)oxy)phenyl)diindolo[3,2,l-de:3',2',r-ij][l,5]na phthyridine-6,13- dione), Cibalackrot Dimer F:

[00200] A mixture of 9 (180.2 mg, 0.204 mmol), 1,3-phenyldiboronic acid, bis(pinacol) ester (29.5 mg, 0.09 mmol), potassium carbonate (250 mg, 1.8 mmol), tetrahydrofuran (4 mL), and water (1.2 mL) was deoxygenated by “freeze-pump-thaw”, and backfilled with argon. This was repeated for three times. PdCl2(dppf)DCM (11.2 mg, 0.014 mmol) was added to the mixture. The mixture was deoxygenated and backfilled with argon. This was repeated for three times. The mixture was heated in a 68 °C oil bath for 20 h. This was then allowed to cool, before addition of water (30 mL), the resulting precipitate collected by filtration, and the filtrate was further extracted with dichloromethane (3 x 20 mL). The combined solvent layers were washed with water (3 x 100 mL), brine (100 mL), then recombined with the collected solid, before filtering through a short plug of silica. The filtrate was collected and the solvent was removed to give a dark red solid, which was purified by column chromatography over neutralised silica (0.5% triethylamine) using dichlormethane/toluene (5:1), and chloroform as eluent, before precipitation from chloroform/toluene (1:1) to give the Cibalackrot Dimer F as a red solid (82.3 mg, 58%); (500 MHz, CHCls): d 0.87-0.91 (12 H, m, Ciba-CH ), 1.25-1.46 (64 H, m, Ciba-CH ₂ ), 1.85 (2 H, p, / = 6.0, CH), 3.97 (4 H, d, /= 6.0, OCH ₂ ), 7.11 & 7.70 (8 H, AA'XX', Ph-H), 7.16-7.26 (5 H, m, mPh-H & Ciba-H), 7.58 (4 H, td, / = 7.0 & 4.0, Ciba-H), 7.64 (1 H, t, / = 7.0, mPh-H), 7.72-7.78 (5 H, m, mPh-H & Ciba- H), 7.88 & 7.92 (8 H, AA'XX', Ph-H), 8.07 (1 H, t, / = 2.0, mPh-H), 8.54 (4 H, tt, / = 8.0 & 1.0, Ciba-H).

EXAMPLE 7

Preparation of 14,14'-([l,l':4',l"-terphenyl]-4,4"-diyl)bis(7-(4-(2- octyldodecyl)oxy)phenyl)diindolo[3,2,l-de:3',2',l'-ij][l,5]n aphthyridine-6,13- dione), Cibalackrot Dimer G:

[00201] A mixture of 9 (180 mg, 0.203 mmol), 1,4-phenyldiboronic acid (15 mg, 0.09 mmol), potassium carbonate (250 mg, 1.8 mmol), tetrahydrofuran (4 mL), and water (1.2 mL) was deoxygenated by “freeze-pump-thaw”, and backfilled with argon x 3. PdCl ₂ (dppf)DCM (9 mg, 0.01 mmol) was added to the mixture. The mixture was deoxygenated and backfilled with argon. This was repeated for three times. The mixture was heated in a 68 °C oil bath for 48 h. This was then allowed to cool, before addition of water (30 mL), the resulting precipitate collected by filtration, and further washed with water, then methanol to give a dark red solid, which was purified by column chromatography over neutralised silica (0.5% triethylamine), using chloroform/toluene (5:1), then chloroform, followed by precipitation from chloroform/toluene (3:1) to give the Cibalackrot Dimer G as a red solid (~30 mg, >20%); ¹ H NMR (300 MHz, CDCb/TFA): d 0.83-0.92 (12 H, m, Ciba-CHs), 1.25-1.57 (64 H, m, Ciba-CH ₂ ), 1.87 (2 H, p, /= 6.0, CH), 3.97 (4 H, d, /= 6.0, OCH ₂ ), 7.10 & 7.60 (8 H, AA'XX', Ph-H), 7.20- 7.26 (4 H, m, Ciba-H), 7.53 (4 H, tt, / = 8.0 & 2.0, Ciba-H), 7.67 (4 H, t, / = 8.0, Ciba- H), 7.77 & 7.88 (8 H, AA'XX', Ph-H), 7.85 (4 H, s, pPh-H), 8.46 (4 H, d, / = 8.0, Ciba- H).

EXAMPLE 8

Preparation of 14,14 ^, -((9,9,9 ^, ,9 ^, ,9 ,9 -hexahexyl-9H,9'H,9 H-[2,2 ^, :7 ^, ,2 - terfluorene]-7,7"-diyl)bis(4,l-phenylene))bis(7-(4-2- octyldodecyl)oxy)phenyl)diindolo[3,2,l-de:3',2',l'-ij][l,5]n aphthyridine-6,13- dione), Cibalackrot Dimer H:

[00202] A mixture of 9 (85 mg, 0.096 mmol), 2,2'-(9,9,9',9',9",9"-hexahexyl- 9H, 9Ή,9"H-[2,2':7', 2"-terfluorene]-7,7"-diyl)bis(4, 4,5, 5-tetramethyl- 1,3,2- dioxaborolane) (50.1 mg, 0.04 mmol), 2 M potassium carbonate solution (0.12 mL, 0.24 mmol), t c t ra - /7 - b u t y 1 a m m o n i u m bromide [TBAB] (45 mg, 0.139 mmol), and toluene (1 mL), deoxygenated under vacuum, and backfilled with argon x 3. Pd(PPh3)4 (10 mg, 0.009 mmol) was added to the mixture. The mixture was deoxygenated and backfilled with argon. This was repeated for three times. The mixture was heated in a 110 °C oil bath for 2 h. This was then allowed to cool, then taken up in chloroform (30 mL), and washed with water (3 x 50 mL), saturated sodium bicarbonate solution (50 mL), brine (50 mL), dried over anhydrous magnesium sulphate, and filtered. The filtrate was collected and the solvent was removed to give a red solid, which was purified by column chromatography over neutralised silica (2% triethylamine) using d i c h 1 o ro met h a n c/n- hexane/toluene (7:3:0.4) as eluent to give the Cibalackrot Dimer H as a red solid (12 mg, >11%); ^l U NMR (500 MHz, CD ₂ C1 ₂ ): d 0.79-0.87 (30 H, m, CH ₂ & CH -L1), 0.89- 0.93 (12 H, m, CH -Ciba), 1.11-1.21 (36 H, m, CH ₂ -L1), 1.28-1.49 (64 H, m, Ciba-CH ₂ ), 1.89 (2 H, p, / = 6.0, CH ₂ ), 2.17-2.20 (8 H, m, L1-CH ₂ ), 4.01 (4 H, d, / = 6.0, OCH ₂ ), 7.13 & 7.71 (8 H, AA'XX', Ph-H), 7.26-7.30 (4 H, m, Ciba-H), 7.60 (4 H, td, / = 8.0 & 3.0, Ciba-H), 7.72-7.82 (16 H, m, Ll-H & Ciba-H), 7.87-7.97 (14 H, m, Ph-H & Ll-H), 8.52 (4 H, t, 7 = 8.0, Ciba-H). EXAMPLE 9

Preparation of 7-(furan-2-yl)-14-(4-((2-octyldodecyl)oxy)phenyl)-diindolo[3 ,2,l- de:3',2',r-ij][l,5]naphthyridine-6,13-dione, Cibalackrot I:

Preparation of ethyl 2-iodoacetate, 10:

[00203] Ethyl 2-bromoacetate (4.6 mL, 41.5 mmol) was added to a solution of sodium iodide (6.9 g, 46.2 mmol) in dry acetone (70 mL, 0.6 M) under argon at r.t. Once addition was complete the mixture was left in the dark for 21 h. Brine (100 mL) was added to mixture. The mixture was extracted with diethyl ether (3 x 60 mL). The ether extracts were combined, washed with sodium metabisulphite solution (100 mL), water (2 x 100 mL), brine (2 x 100 mL), dried over anhydrous magnesium sulphate and filtered through a short plug of silica. The filtrate was collected and the solvent was removed to give 10 as a light orange oil (8.84 g, 95%); NMR (300 MHz, CDCL): d 1.28 (3H, t, / = 7.0, CH ₃ ), 3.68 (2 H, s, I-CH ₂ ), 4.20 (2 H, q, / = 7.0, O-CH2).

Preparation of ethyl 2-(furan-2-yl)acetate, 11:

[00204] 30% H2O2 (5.6 mL, 78 mmol) was added dropwise to a cooled (~10 °C; ice/water bath) solution of 10 (5.09 g, 23.8 mmol), furan (30 mL, 424 mmol), iron(II) sulphate heptahydrate (3.32 g, 11.9 mmol) in DMSO (100 mL). Once addition was complete the mixture was left at r.t. for 20 h under argon. Brine (150 mL) was added, and the resulting oil was extracted with diethyl ether (5 x 75 mL). The combined diethyl ether layers were then washed with water (3 x 100 mL), brine (2 x 100 mL), dried over anhydrous sodium sulphate, then filtered through a short plug of silica. The filtrate was collected and the solvent was removed to give 11 as a light yellow oil (3.6 g, 96%); ¹ H NMR (300 MHz, CDCL): d 1.27 (3 H, t, J = 7.0, CH ), 3.68 (2 H, s , Lur-CH ₂ ), 4.19 (2 H, q, / = 7.0, CH ₂ ), 6.22 (1 H, dq, / = 3.0 & 1.0, Lur-H), 6.33 (1 H, dd, / = 3.0 & 2.0, Lur-H), 7.36 (1 H, dd, / = 2.0 & 1.0, Lur-H).

Preparation of 2-(furan-2-yl)acetic add, 12:

[00205] 4 M sodium hydroxide solution (1.8 mL, 7.2 mmol) was added to a solution of 11 (1 g, 6.41 mmol) in ethanol (1 mL). Once addition was complete, the mixture was stirred under argon at r.t. for 18 h, then quenched with 3M hydrochloric acid (50 mL). The resulting mixture was extracted with diethyl ether (5 x 30 mL), then the combined diethyl ether layers were washed with brine (2 x 50 mL), then dried over anhydrous sodium sulphate and filtered. The filtrate was collected and the solvent was removed to give 12 as an off-white crystal (720 mg, 89%); ¹ H NMR (300 MHz, CDCL): d 3.74 (2 H, s, CH ₂ ), 6.26 (1 H, dq, / = 3.0 & 1.0, Fur-H), 3.65 (1 H, dd, / = 3.0 & 2.0 Fur-H), 7.38 (1 H, dd, / = 2.0 & 1.0, Fur-H).

Preparation of 2-(furan-2-yl)acetyl chloride, 13:

[00206] A solution of 12 (201 mg, 1.6 mmol) in thionyl chloride (0.8 mL, 7.8 mmol) was heated in a 55 °C oil bath under argon for 4 h. This was allowed to cool and the excess thionyl chloride was removed under vacuum to give 13 as a red oil (230 mg, -100%); ^l U NMR (300 MHz, CDCb): d 4.20 (2 H, s, CH ₂ ), 6.33(1 H, dq, / = 3.0 & 1.0, Fur-H), 6.37-6.39 (1 H, dd, /= 3.0 & 2.0, Fur-H), 7.41 (1 H, dd, / = 2.0 & 1.0, Fur-H).

Preparation of 7-(furan-2-yl)-14-(4-((2-octyldodecyl)oxy)phenyl)diindolo[3, 2,l- de:3',2',l'-ij][l,5]naphthyridine-6,13-dione, Cibalackrot I:

[00207] A mixture of 8 (101 mg, 0.154 mmol), and 12 (230 mg, 1.6 mmol) in p-xylene (1.7 mL) was heated in a 145 °C oil bath under a flow of nitrogen for 14 h. This was allowed to cool, and petroleum spirit (30 mL) was added and the resulted precipitate was collected on a pad of celite, and washed further with petroleum spirits, and ethanol until clear. The product was taken up in chloroform and filtered through a plug of celite. The filtrate was collected and the solvent was removed to give a dark solid, which was purified by column chromatography over silica using chloroform as eluent to give the Cibalackrot I as a dark purple solid (40 mg, 35%); ^X H NMR (300 MHz, CDCb): d 0.86- 0.91 (6 H, m, CH3), 1.26-1.41 (32 H, m, CH ₂ ), 1.80-1.87 (1 H, m, CH), 3.95 (2 H, d, / = 6.0, OCH2), 6.75 (1 H, dd, / = 3.5 & 2.0, Fur-H), 7.09 & 7.67 (4 H, AA'XX', Ph-H), 7.20- 7.25 (1 H, m, Cbk-H), 7.42 (1 H, td, /= 8.0 & 2.0, Cbk-H), 7.56 (1 H, td, / = 8.0 & 1.5, Cbk-H), 7.58-7.63 (1 H, m, Cbk-H), 7.66-7.71 (1 H, m, Cbk-H), 7.83 (1 H, d, / = 2.0, Fur-H), 7.87 (1 H, dd, / = 4.0 & 1.0, Fur-H), 8.59 (2H, t, J = 9.0, Cbk-H), 8.74 (1 H, d, / = 8.5, Cbk-H).

EXAMPLE 10

Preparation of 14,14'-((9,9-dihexyl-9H-fluorene-2,7-diyl)bis(furan-5,2-diyl ))bis(7- (4-((2-octyldodecyl)oxy)phenyl)diindolo[3,2,l-de:3',2',r-ij] [l,5]naphthyridine- 6,13-dione), Cibalackrot Dimer J:

Preparation of 7-(5-bromofuran-2-yl)-14-(4-((2-octyldodecyl)- oxy)phenyl)diindolo[3,2,l-de:3',2',r-ij][l,5]naphthyridine-6 ,13-dione, 14:

[00208] /V-bromosuccinimide (11.2 mg, 0.063 mmol) was added to a solution of the Cibalackrot I (40 mg, 0.053 mmol) in dry chloroform (1 ruL) under argon. The reaction was allowed to stir in the dark for 1 h, then diluted with chloroform (10 mL) and filtered through a short plug of silica, flushing with additional chloroform (10 mL). The filtrate was collected and the solvent was removed to give a dark purple solid, which was purified by column chromatography over silica using chloroform/petroleum spirits (9:1, with 0.2% triethylamine) as eluent to give 14 as a dark purple solid (25 mg, 57%); ¹ H NMR (300 MHz, CDCb): d 0.86-0.92 (6 H, m, CH ₃ ), 1.26-1.50 (32 H, m, CH ₂ ), 1.81— 1.89 (1 H, m, CH), 3.95 (2 H, d, / = 6.0, OCH ₂ ), 6.61 (1 H, d, / = 4.0, Fur-H), 7.09 & 7.67 (4 H, AA'CC', Ph-H), 7.20 (1 H, td, / = 8.0 & 1.5, Ciba-H), 7.40 (1 H, td, / = 8.0 & 1.5, Ciba-H), 7.48-7.59 (2 H, m, Ciba-H), 7.64-7.67 (1 H, m, Ciba-H), 7.76 (1 H, d, / = 4.0, Fur-H) , 8.47 (1 H, qd, /= 8.0 & 1.0, Ciba-H), 8.54 (1 H, qd, /= 8.0 & 1.0, Ciba-H), 8.70 (1 H, dq, / = 8.0 & 1.0, Ciba-H).

Preparation of 14,14'-((9,9-dihexyl-9H-fluorene-2,7-diyl)bis(furan-5,2-diyl ))bis(7- (4-((2-octyldodecyl)oxy)phenyl)diindolo-[3,2,l-de:3',2',r-ij ][l,5]naphthyridine- 6,13-dione), Cibalackrot Dimer J:

[00209] A mixture of 14 (25 mg, 0.03 mmol), 2,2'-(9,9-dihexyl-97/-fluorene- 2,7-diyl)bis(4,4,5,5-tetramethyl-l,3,2-dioxaborolane) (8.1 mg, 0.014 mmol), potassium carbonate (11.6 mg, 0.084 mmol), tetrahydrofuran (0.6 mL), and water (0.15 mL) was deoxygenated by “freeze-pump-thaw” under vacuum and backfilled with argon. This was repeated for three times. PdCl2(dppf)DCM (0.8 mg, 0.001 mmol) was added to the mixture. The mixture was deoxygenated and backfilled with argon. This was repeated for three times. The mixture was heated in a 65 °C oil bath for 14 h. This was then allowed to cool, before addition of water (20 mL), and extraction with chloroform (3 x 20 mL). The chloroform extracts were combined and washed with water (3 x 50 mL), brine (50 mL), dried over anhydrous sodium sulphate and filtered. The filtrate was collected and the solvent was removed to give a dark blue solid, which was purified by pulling through a short plug of silica using toluene/petroleum spirits (1:1, with 0.2% triethylamine), precipitating from ethyl acetate, and washing with diethyl ether, before column chromatography on neutral aluminum oxide using toluene as eluent to give the Cibalackrot Dimer J as a dark blue solid (6 mg, 30%); ^X H NMR (500 MHz, CD2CI2): d 0.74 (6 H, t, / = 7.0, FI-CH3), 0.77-0.86 (4 H, m, F1-CH ₂ ), 0.87-0.91 (12 H, m, Ciba- CH ), 1.05-1.20 (12 H, m, F1-CH ₂ ), 1.26-1.47 (64 H, m, Ciba-CH ₂ ), 1.87 (2H, p, / = 6.0, CH), 2.14 (4 H, t, / = 8.0, F1-CH ₂ ), 3.99 (4 H, d, / = 6.0, OCH ₂ ), 7.05 (2 H, d, / = 4.0, Fur-H), 7.09 & 7.66 (8 H, AA'XX', Ph-H), 7.18 (2 H, t, / = 8.0, Ciba-H), 7.31 (2 H, t, / = 8.0, Ciba-H), 7.51 (2H, t, /= 8.0, Ciba-H), 7.58-7.61 (4 H, m, Ciba-H), 7.77 (2 H, d, / = 8.0, Fl-H), 7.90-7.92 (6 H, m, Fl-H & Frn-H), 8.84 (2 H, d, / = 8.0, Ciba-H), 8.55 (2 H, d, / = 8.0, Ciba-H), 8.97 (2 H, d, / = 8.0, Ciba-H).

Thermal Properties

[00210] The thermal properties of Cibalackrot A and B were studied using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) both chromophores were found to have excellent thermal stability with 5% weight loss temperature, T _d( 5%), at 402 °C and 419 °C, for A and B, respectively, similar to those of conjugated bay-annulated indigo derivatives synthesized by He el al, J. Am. Chem. Soc. 2014, 136, 15093, indicating that the surface groups do not alter their thermal stability. DSC traces of A and B at a scan rate of 200 °C min ¹ were obtained. Three endothermic transitions were observed in the heating cycle of Cibalackrot A. Given that the melting point of Cibalackrot A (-306-309 °C) was higher than the upper limit of the DSC used, these endothermic processes indicate multiple crystal-crystal transitions/rearrangements upon heating. There were no thermal transitions found for Cibalackrot B, likely due to the more amorphous in nature of the material caused by attachment of the branched solubilising groups.

Electrochemical Properties

[00211] The electrochemical properties of Cibalackrot A and B were probed in solution by using cyclic voltammetry with a conventional three-electrode setup and ferrocenium/ferrocene (Fc ⁺ /Fc) redox couple as the reference. Both chromophores showed chemically reversible redox processes under repeated scans. With these reversible redox waves, their highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels from their 1 ^st redox potentials were estimated, using the work function of ferrocene as -4.8 eV versus vacuum level. This gave the estimated HOMO energy values of -5.63 and -5.57 eV for Cibalackrot A and B, respectively, and LUMO energy values of -3.45 and -3.43 eV, respectively. The slightly destabilised HOMO and LUMO energy levels of Cibalackrot B (relative to A) can be attributed to the slightly electron richness of the alkoxy surface groups attached (i.e. inductive effect to the central active core), which have a relatively stronger electron donating nature than the n-dodccyl substituents in Cibalackrot A. From the estimated HOMO and LUMO energy values, electrochemical bandgaps for Cibalackrot A and B were determined to be 2.18 and 2.14 eV, respectively, and is in agreement with the observed optical bandgap trend resulting from their solution absorption and emission spectra (below).

Photophysical Properties and Theoretical Calculations

[00212] Photophysical properties of Cibalackrot A and B were probed in solution, neat films (spin coated from 10 mg mL ¹ chloroform solution) and blend films [5wt% Cibalackrot A in mCP and CBP; l-5wt% Cibalackrot A and B in mCP:HBT (4:1 by weight) mixed host]. Figure la shows their steady state solution absorption in dichloromethane and photoluminescence (PL) spectra in toluene. In dichloromethane, Cibalackrot A and B have absorption peaks at 544 and 554 nm, respectively, corresponding to 0-0 vibronic transition. Both Cibalackrot A and B also showed other vibronic transitions, 0-1 transition at 508 and 518 nm, respectively, and S0-S2 transition at 372 and 383 nm, respectively. Similarly, the solution PL spectra of Cibalackrot A and B showed vibronic features with respective maxima at 582 and 592 nm corresponding to their 0-0 transitions, and at 626 and 637 nm, respectively, corresponding to their 0-1 transitions. The transitions for Cibalackrot B are slightly red-shifted relative to those for Cibalackrot A due to slightly destabilised HOMO.

[00213] Figure 2 shows the normalised absorption and PL spectra of neat Cibalackrot A and Cibalackrot B films overlapped with PL spectra of mCP, CBP and mCP:HBT mixed host. Neat-film PL spectra of Cibalackrot A and B were found to be red-shifted as compared to those in solution due to strong intermolecular interaction between the chromophores in the solid state. This also leads to significantly reduced PLQYs (~7%) in the neat films (Table 1). Hence, in order to suppress the aggregate induced luminescence quenching, a molecular doping approach was used, in which the dyes were blended into suitable hosts to allow energy transfer from the host to the emitter. The efficiency of FRET crucially depends on the spectral overlap between the absorption of the guest molecule and emission of the host. The emission spectra of mCP:HBT mixed host showed large overlap with the S0-S1 absorption band of Cibalackrot A and B, while on the other hand, the PL of mCP and CBP showed dominant overlap with their S0-S2 absorption bands.

[00214] Figure lb shows the absorption and normalised PL spectra of 5wt% Cibalackrot A in different hosts. The absorption spectrum of the blend is dominated by mCP absorption with a peak at 342 nm and a shoulder at 356 nm, which can be attributed to HBT absorption. Broadening of the PL spectrum was observed with the increase of dopant concentration. Along with the slight red shift in PL, this indicates aggregate induced quenching at higher dye loadings.

[00215] Solution and solid state PLQYs and excited-state lifetimes of Cibalackrot A and B were measured at various blend ratios as summarised in Table 1. The excited-state lifetimes were estimated from TCSPC fluorescence decay in toluene solution, as shown in Figure 3a and 3b, for blend films and for solution (in toluene), respectively. While the photophysical properties of Cibalackrot A and B were comparable in toluene solutions, Cibalackrot B showed slightly higher radiative rates (k,-) in the mixed host films than those of Cibalackrot A. This can be in part attributed to relatively inefficient energy transfer from HBT to Cibalackrot A at lower doping concentration as can be seen from the higher rise times (-480 ps for lwt% doping of Cibalackrot A) of TCSPC plot which drops down to -180 ps for 5wt% doping, close to the instrument response function (-150 ps) of the measurement setup. The reduction in PLQYs for 4 and 5wt% blend films of Cibalackrot A and B is due to aggregation induced quenching becoming more dominant than the improved FRET at higher doping concentrations. Further evidence of this quenching effect was observed in the reduced excited-state lifetimes, estimated from TCSPC decay with increasing doping concentrations.

[00216] Table 1. Photophysical properties of Cibalackrots A and B in toluene solution and l-5wt% blended in the mixed host [mCP:HBT (4:1 by weight)] as well as neat films.

Cibalackrot A Cibalackrot B

PLQY Lifetime k _r PLQY Lifetime kr

(%) (ns) (xlO ⁸ s ¹ ) (%) (ns) (xlO ⁸ s ¹ ) in toluene 99+1 6.30 1.58 96+1 6.19 1.56 lwt% blend film 60+6 7.39 0.81 70+7 5.94 1.17 2wt% blend film 69+7 7.01 0.98 78+8 5.61 1.38 3wt% blend film 75+7 6.80 1.11 71+7 5.32 1.34 4wt% blend film 69+7 6.58 1.05 61+6 5.08 1.19 5wt% blend film 55+6 5.88 0.94 55+6 4.87 1.13 neat film 8+2 6+2

[00217] Photophysical properties of Cibalackrot I were probed in toluene solution and the steady state solution absorption and PF spectra are shown in Figure 4. High PFQY (87%) and short excited-state lifetime (5.16 ns) were found for Cibalackrot I, as summarised in Table 2.

[00218] Table 2. Photophysical properties of Cibalackrot I in toluene solution.

Cibalackrot I

PLQY Lifetime k _r

(%) (ns) (xlO ⁸ s ¹ ) in toluene 87 5.16 1.69

[00219] Photophysical properties of Cibalackrot Dimers E-G and J were probed in solution, neat (spin coated from 10 mg mF ¹ chloroform solution) and blend films (0.5- 8.0wt% Cibalackrot Dimers E & F in F8BT). Figure 5 shows the normalised steady state solution absorption and PF spectra of Cibalackrot Dimers E-G and J in toluene. Figures 6 and 7 show their steady state neat and blend films (0.5-8.0wt% in F8BT) absorption and PF spectra of Cibalackrot Dimers E and F, respectively. The solution PFQYs and excited-state lifetimes of Cibalackrot Dimers E and F in toluene and films are summarised in Table 3. The solution PFQYs and excited- state lifetimes of Cibalackrot Dimers G and J in toluene are summarised in Table 4.

[00220] Table 3. Photophysical properties of the Cibalackrot Dimers E and F in toluene solution and l-8wt% blended in F8BT as well as neat films. Cibalackrot Dimer E Cibalackrot Dimer F

PLQY Lifetime h PLQY Lifetime h

(%) (ns) (xlO ⁸ s ¹ ) (%) (ns) (xlO ⁸ s ¹ ) in toluene 96 4.17 2.31 97 4.92 1.98 0.5wt% blend film 100+3 3.77 2.66 92+4 5.24 1.76 lwt% blend film 98+2 4.55 2.16 91+3 4.98 1.82 2wt% blend film 85+2 3.93 2.17 90+3 5.10 1.77 4wt% blend film 69+1 3.62 1.90 79+2 5.51 1.44 8wt% blend film 50+1 3.58 1.40 36+1 6.30 0.58 neat film 13+2 3.82 0.33 4+2

[00221] Table 4. Photophysical properties of the Cibalackrot Dimers G and J in toluene solution.

Cibalackrot Dimer G Cibalackrot Dimer J

PLQY Lifetime h PLQY Lifetime h

(%) (ns) (xlO ⁸ s ¹ ) (%) (ns) (xlO ⁸ s ¹ ) in toluene 89 4.08 2.17 >20 2.90 >0.70

Transient Absorption Spectroscopy Measurements

[00222] One important parameter that limits the performance of an organic laser dye is absorption of excited states such as triplets and singlets. Specifically, triplet- absorption and quantum yield of triplet excited-state not only add to the excited-state absorption losses but also act as a barrier to laser operation under longer excitation pulse widths due to the long-lived nature of the triplets, which further leads to the issue of triplet pile-up. Nano-second (ns) transient absorption spectroscopy (TAS) performed to gain more insight into the excited-state absorption of the Cibalackrot derivatives. No long- lived excited state feature was detected in transient spectra of Cibalackrot B in toluene

(optical density ~0.2 at 525 nm) measured at different time delays at pump intensity of

20 pw. The short-lived features were found to have lifetimes of -6.2 ns which was same as that obtained from TCSPC decay plots and hence can be assigned to singlet excited- state absorption. Absence of any triplet absorption feature can be attributed to extremely low triplet yield of these materials due to nearly 100% PLQY. However, it is still important to track the triplet absorption spectra since even the smallest triplet absorption signal in emission wavelength can be detrimental to lasing. A change of solvent from toluene to bromobenzene to induce solvent assisted intersystem crossing still failed to produce long-lived features at low pump intensities. Upon increasing the pump intensity to 500 pw, an extremely low signal (<1 mOD) from the long-lived triplet states was obtained. The lifetime of this feature was found to be ~512 ns for Cibalackrot B. The presence of triplet excited- states was confirmed by further increasing the pump excitation intensity to 1.3 mw (Figure 8); similar long-lived feature with lifetime of ~522 ns was obtained. The triplet excited-state spectrum was found to overlap with the PL emission. However, the optical density at the triplet absorption peak (< 4 mOD) was 20 times lower than that of the singlet absorption (~80 mOD at 844 nm) and the stimulated singlet emission (~100 mOD at 590 nm). Assuming all non-radiative losses incurred to be due to the triplet excited states, extremely low inter-system crossing rate (Arse) of < 7.2><10 ⁶ s ¹ was calculated for Cibalackrot B, while triplet absorption coefficient (et-t) and triplet st- _T cross section were approximated to be 35062 L mol ¹ cm ¹ and 1.34 xlO-16 cm ² at 642 nm from net ground state bleach. These results suggest low optical losses to triplet absorption in the gain media under optical excitation, which is beneficial to achieve good lasing properties.

Amplified Spontaneous Emission and Photostability Studies

[00223] The lasing properties of OSSLs can strongly depend upon the type of optical cavity used for amplification; hence, ASE properties were studied to understand the efficacy of the Cibalackrot derivatives as organic laser dyes. To get the ASE characteristics, samples were optically excited at various input intensities using a nitrogen laser emitting at 337 nm and the PL spectrum was collected from the edge of the samples. The threshold for ASE was determined by plotting output intensity from the edge of the sample versus the input excitation intensity. The abrupt change in slope of the input versus output curve along with reduced full-width-at-half-maximum (FWHM) of the PL spectra gives the onset of ASE or the ASE threshold ( E _th ).

[00224] ASE characteristics were first investigated for 150 nm thin films of 5wt% Cibalackrot A blended in CBP, mCP and mCP:HBT mixed host. The threshold in the mCP:HBT mixed host was found to be 25.6+0.7 pj cm ² ( A _SE = 638 nm), which was slightly lower than those obtained in mCP (27.2+1.0 pJ cm ² , A _SE = 640 nm) and CBP hosts (32+1.7 pJ cm ² , A _SE = 641 nm). The spectral narrowing effect was clearly seen in ah samples with FWHM dropping down to 10 nm at higher pumping intensities. These threshold numbers are comparable to other red and deep-red laser dyes at doping concentrations of 5wt% or higher.

[00225] Notably, apart from low threshold, the mixed host showed increased photostability. The photostability was studied by using blend films of 5wt% Cibalackrot A in the different hosts and pumped at constant pump intensity just below the ASE threshold and at intensity twice the threshold (2 x £*) with operating frequency of 20 Hz, and the evolution of emission intensity from ASE peak was plotted as a function of time and number of pump pulses. As shown in Figure 9a, the mixed host showed lower irreversible degradation both above and below the threshold pump intensity. Interestingly, narrow ASE spectrum was retained in mixed host even after 2,000 pump pulses when pumped at intensity twice the threshold. Both of the single component hosts showed broadening of the spectrum as a signature of transition from ASE to spontaneous emission after 100-200 pump pulses. The evolution of the spectrum as a function of time and the normalised PL spectrum of Cibalackrot A in different hosts after 1 and 100 seconds are shown in Figure 9b for pump intensity twice the ASE threshold. Improved photostability in mCP:HBT mixed host can be attributed to energy transfer at a longer wavelength (lower energy region) from HBT to Cibalackrot A. Large Stokes shifts of HBT, arising from excited-state intramolecular proton transfer (ESIPT), allow efficient cascade energy transfer from mCP to HBT and then to Cibalackrot. Use of the mixed host leads to sufficient absorption at the pump wavelength with efficient energy transfer to the emitter, as well as a reduced gap between energy transferred and energy emitted by the dye. Hence, leading to lower heat dissipation in the emitter via non-radiative processes.

[00226] ASE characteristics were then optimised in mixed host for Cibalackrots

A and B by varying the doping concentrations of the emitter from 1-5 wt%. The lowest thresholds, 15.6+0.6 pJ cm ² for 3wt% doped Cibalackrot A, and 13.1+0.3 pJ cm ² for

2wt% doped Cibalackrot B were achieved in 150 nm thick films. To further optimise the

ASE thresholds, the thickness of 2wt% Ciblackrot B and 3wt% Cibalackrot A blend films was varied from 130 to 320 nm (Figure 10) by varying the spin-coating speeds. An extremely low ASE threshold of 9.6+0.6 pJ cm ² was achieved with a film thickness of

~230 nm for films of 2wt% Cibalackrot B in mCP:HBT. Comparison to reported materials showing ASE and lasing with red and deep-red emission wavelengths were recently summarised in paper by M. Mamada et al, Adv. Fund. Mater. 2018, 28, 1706023. Figure 10 shows the best ASE performance obtained for Cibalackrots A and B. Thickness dependent ASE threshold can be attributed to the strength of waveguide formed in the organic layer, similar thickness dependence has previously been reported for other organic materials. The ASE thresholds reported here are comparable to the best- reported ASE thresholds for red and deep-red emitting materials [H. Rabbani-Haghighi et al., Appl. Phys. Lett. 2009, 95, 033305; A. Vembris et ah, Opt. Laser Technol. 2017, 95, 74; D.-H. Kim et al, Nat. Photonics 2018, 12, 98]. Photo stability of 230 nm thick films of 2wt% doped Cibalackrot B in mixed host were also investigated at pump intensity of 2 x £ _th (~20 pj cm ² ) as shown in Figure 11. It was observed that there is very marginal drop in ASE output intensity with 90% of the initial output retained even after ~9,600 pump pulses of continuous pumping at 20 Hz. These photostability results are superior to some of the most highly performing organic laser dyes which show line narrowing in the red and deep red part of the spectrum, though the pump intensity used in previously reported works should be taken into account. For direct comparison, perylenediimide derivatives show more than 40% reduction in intensity when pumped at intensity twice the ASE threshold [R. Munoz-Marmol, et al., J. Phys. Chem. C 2018, 122, 24896; E. M. Calzado, et al., J. Phys. Chem. C 2007, 111, 13595] (l _riphr >500 nm) while a recently reported Squaraine derivative [H. Ye, et al., ACS Appl. Mater. Interfaces 2018, 10, 27] showed extremely rapid photo degradation even at intensities below the threshold when pumped using a N2 laser similar to the one used in this work.

[00227] Solid state ASE characteristics of Ciblackrot Dimers E and F (lwt% in F8BT) were measured to give thresholds of 12.9 and 15.2 pj cm ² , respectively, as shown in Figures 12 and 13, respectively.

Distributed Feedback Laser Operation

[00228] Subsequent to testing the photo stability and ASE properties of the Cibalackrot derivatives, laser operation employing a first order DFB grating resonator structure was studied. This structure was selected specifically because the output coupling losses in case of first-order feedback structures are comparatively lower, further leading towards low lasing thresholds. The amplification wavelength in case of DFB structure depends on the Bragg condition defined as: in _/. = 2« _eff A, where m is the order of the grating, l is the wavelength of light, n _{e ff} the effective refractive index of the gain medium, and L is the period of the DFB structure. The optical constants for 2wt% Cibalackrot B blended in the mixed host were measured using variable angle spectroscopy for a 150 nm thick sample. Using the optical constants and amplification wavelength obtained in the ASE measurements, the grating period for first-order diffraction was chosen to be 200 nm. A 260 nm thick film of 2wt% Cibalackrot B in the mixed host was then spin coated on top of the DFB structure. As shown by the change in slope of input versus output curve in Figure 14a, an extremely low lasing threshold of 6+0.3 pJ cm ² was obtained for this laser device with amplification wavelength of 641 nm and FWHM of 1.1 nm (Figure 14b). This lasing threshold is comparable to that reported for one of the most commonly used high performing red organic laser dyes, DCM2, [D. Schneider et al., Appl. Phys. Lett. 2004, 85, 1886] doped in semiconducting host. It was discovered that the lasing wavelength achieved using Cibalackrot B can be further tuned by varying the period as well the thickness of the organic waveguide. This observation is consistent with DFB theory. In order to evaluate the optical gain in Cibalackrot B, the absorption, stimulated emission and triplet excited state absorption cross sections were estimated [A. S. D. Sandanayaka et al., Sci. Adv. 2017, 3, el602570]. Even though the triplet excited state absorption spectra of Cibalackrot B overlaps with the DFB laser emission, T-T absorption cross section was found to be one order lower in magnitude than absorption and emission cross sections. This property also makes Cibalackrot derivatives a probable candidate for quasi-CW lasing.

[00229] The disclosure of every patent, patent application, and publication cited herein is hereby incorporated herein by reference in its entirety.

[00230] The citation of any reference herein should not be construed as an admission that such reference is available as "Prior Art" to the instant application.

[00231] Throughout the specification the aim has been to describe the preferred embodiments of the invention without limiting the invention to any one embodiment or specific collection of features. Those of skill in the art will therefore appreciate that, in light of the instant disclosure, various modifications and changes can be made in the particular embodiments exemplified without departing from the scope of the present invention. All such modifications and changes are intended to be included within the scope of the appended claims.