One class of compounds which have been proposed as having potentially valuable conduction properties are macrocyclic compounds which are capable of forming columnar stacks in the solid state. Examples of such compounds include phthalocyanines and porphyrins. The formation of metal complexes of such compounds or the introduction of suitable dopants has been found to enhance the conduction properties of these compounds. These prior proposals have all been directed to compounds wherein the mode of conduction is electronic.

We have now discovered that derivatives of macrocyclic compounds which comprise substituents which are capable of interacting to form a hydrogen bond may exhibit proton conductivity. Furthermore, the bond formation facilitates the formation of ordered molecular stacks and this enhances the ability to form useful conducting materials.

Accordingly, from one aspect this invention provides a molecular-electronic device wherein the conducting material comprises a macrocyclic compound which is capable of forming columnar stacks wherein said compound comprising at least one substituent capable of forming a hydrogen bond as part of its molecular structure. In a preferred embodiment the conducting material is such that the mode of conduction is at least partially that of proton conduction. The derivatives which we have found to be useful are those which contain substituents which facilitate the formation of hydrogen bonds between the molecular layers in the columnar stack. The nature of the substituent groups which are capable of forming such bonds is well known in the art. The preferred derivatives for use according to this invention are those in

which at least three and more preferably at least four sites at which hydrogen bonds may be formed are present. These substituents are preferably situated symmetrically at different positions on the macrocyclic compounds. The preferred substituents which may be introduced into the macrocyclic compounds in order to form the derivatives useful according to this invention are those which contain at least one hydroxyl , carbox late, primary amine or secondary amine function.

A preferred group of macrocyclic compounds from which derivatives useful according to this invention may be prepared are the tetrapyrolic macrocycles especially the porphyrins and the phthalocyanines.

Especially valuable for use are the porphyrins of the Formula I

wherein R , R , R3 and R which may be the same or different represent a monovalent group comprising a heterocyclic ring comprising at least one nitrogen atom. The preferred compounds are those wherein the substituents R are identical and represent an imidazole pyrimidine or purine group. The most preferred compounds are those in which a nitrogen atom within the heterocyclic ring of the substituent is at the β position relative to the macrocyclic ring. The most preferred compounds are those wherein the substituents R represent imidazole groups and the most preferred compound is mesotetrakis(2-imidazo1yl) porphyrin.

The porphyrins having the Formula I may be prepared by syntheses known in the art. In particular, by the Rothermund synthesis in which pyrrole is added to a solution of an aldehyde having the formula RCHO wherein R represents any of the substituent groups R-j , R , R3, R4 as defined above in propionic acid.

The 1:1 metal complexes of the tetrapyrrolic macrocyclic compounds described above may also exhibit conduction properties and molecular-electronic devices comprising such complexes form a further aspect of this invention. These complexes may be prepared using processes known to be useful in the art. The nickel, palladium and platinum complexes of the porphyrins and phthalocyanines are especially useful and form a preferred aspect of this invention. The ferric iron and cupric copper complexes are also of particular value. The metal complexes may find particular application as a conducting material in molecular-electronic devices since they may exhibit both proton and electronic conduction. Devices wherein the conducting material exhibits this dual conduction capability form another aspect of this invention.

The invention is illustrated by the following examples. Example 1

Mesotetrakis(2-imidazolyl)porphyrin (TIP), was prepared via the Rothemund procedure by refluxing equimolar amounts of imidazole-2-carboxaldehyde and pyrrole in propionic acid. Analytically pure product was obtained by washing the solid precipitated from the cooled reaction mixture with chloroform, acetone and methanol .

The material could not be chromatographed on silica gel. The product was found not to be soluble in neutral aqueous solutions. However, it was soluble in solutions at pH = 2 or less.

Uv/visible spectra recorded between 400 nm and 700 n and from pH = 2 (0.01M HC1 , porphyrin free-base) to pH = -1.08 (12M HC1 , porphyrin dication) did not show a coherent set of pH-

dependant isobestic points for both the B band and Q band spectra.

The IR spectrum of the product ( Br disc) shows a broad, intense absorption between 2400 cm ^-1 and 3600 cm ^-1 , similar to that shown by imidazole.

Samples of TIP were therefore subjected to proton- conductivity studies, along with tetraphenyl porphyrin (TPP) which was used as a non-hydrogen bonded reference compound.

Compressed discs of TIP and TPP were prepared. These were retained between spring-loaded electrodes composed of Pt black electrochemically deposited on a copper substrate in a vacuum- tight environment, in which the partial pressure of water was closely controlled.

Initial D. C. conductivity measurement on a TIP sample under nitrogen, without prior evacuation of the test cell to remove water, gave a conductivity of 1.2*10 ^~6 S m~- . Under the same conditions, the TPP sample gave a much lower conductivity of <3*10 ^-14 S πH . Dehydration of the samples by evacuating the test cell, reduced the conductivity of the TIP to 1.6*10 ^-11 S m ^-1 , while that of the TPP remained virtually unchanged at 1*10 ^"14 S πr ¹ .

Another sample of TIP was evacuated overnight at 10 ^-2 torr, to remove bound water. It was then allowed to equilibrate in the test cell with an atmosphere containing water vapour at 11.3% partial pressure. The conductivity of the TIP sample was then measured and found to be 6.8*10 ^"12 S m~ ^■ . A pulse of dry hydrogen gas was then admitted to the cell and the conductivity was observed to rise by nearly four orders of magnitude to 2.8*10 ^-8 S m ^"1 , demonstrating that conductivity in TIP is protonic and hydration dependant.

Evidence that TIP has a stacked arrangement of monomeric subunits in the solid state has, however, been provided by powder X-ray diffraction studies. While the data obtained could not be unequivocally indexed, solutions obtained by a program were consistent with there being one short crystallographic

axis. Values for the unit cell dimensions obtained in this way are:- a = 3.6±0.2A; b * ^■ = 17.0±0.3A; c = 20.65±0.25A Example 2 The porphyrin mesotetrakis (2-imidazoyl) porphyrin (TIP) ⁽ lO gs; 0.0175mM) was warmed with stirring in dilute hydrochloric acid (0.01M; 3ml) until it dissolved. UV/visible spectroscopy of this solution showed a four banded visible spectrum demonstrating that the TIP is not protonated on its central nitrogen atoms.

A saturated aqueous solution of nickel chloride (lO ls) was then added with warming. The UV/visible spectrum showed a collapse of the four banded spectrum to a two banded spectrum after a period of about three hours. The mixture was allowed to cool to ambient temperature then several drops of 0.880 ammonia were added. The 1:1 nickel porphyrin complex precipitated out leaving the excess nickel in solution in the form of its hexammine complex.