Columnar liquid crystals from wedge-shaped tetrahedral copper(I) complexes

Very stable copper(I) complexes were engineered from pyridine ligands bearing on one side an iminophenyl fragment and on the other a pivotal methyl group. The phenyl group was substituted in the para position either by a methoxy group or by a phenyl ester group grafted with three paraffin chains (n = 8, 12, 16). The methoxy complex in the crystalline state was characterized by X-ray diffraction. Its molecular structure was found to correspond to a distorted tetrahedral arrangement round the copper(I) metal centre. The long-chain complexes near room temperature were found to produce columnar liquid crystals of hexagonal symmetry. The columns were found to result from the aggregation of the wedge-shaped molecules round the columnar axis with the metal-containing iminopicoline ligands crowded together in the centre and the alkyl chains pointing outwards with a disordered conformation. The degree of molecular aggregation, around 7, was found to decrease significantly on heating.