Supramolecular Liquid Crystals Induced by Hydrogen-Bonding Interactions Between Non-Mesomorphic Compounds. I. 4-(4'-Pyridylazophenyl)-4''-Substituted Benzoates and 4-Substituted Benzoic Acids

Equimolar binary mixtures of the title compounds were prepared to investigate the effect of different polar substituents, either on the pyridine-based derivatives or on the acid component, on the extent and stability of the supramolecular liquid crystal phases induced by intermolecular hydrogen bonding. None of the pyridine-based derivative or the acid complement is mesomorphic, but the hydrogen-bonded complexes are. The mixtures prepared were characterized for their mesophase behavior by differential scanning calorimetry, DSC, and polarized light microscopy, PLM. Five azo pyridine-based derivatives (Ia-e), with molecular formula X-C6H4COOC6H4-N=N-C5H4N, were prepared that differ from each other by the substituent X. The latter varies between CH3O, CH3, H, Br, and NO2. Six 4-substitutedbenzoic acids (Y-C6H4COOH, IIa-f) were used; the substituent Y varies between CH3O, CH3, H, Br, CN, and NO2. Nematic mesophase is induced in most of the binary mixtures investigated.