Novel hydrogen-bonded angular supramolecular liquid crystals

Abstract

Two types of new pyridine-based azo dyes, namely, 4-(3′-pyridylazo)-4″-alkoxybenzoates with various alkoxy chains and 4-(3′-pyridylazo)-4″-substituted benzoates bearing groups of different polarities, were prepared and investigated for their mesophase behaviour by differential scanning calorimetry and polarised light microscopy. All homologues of the former group were found to be mesomorphic, while all derivatives of the latter are non-mesomorphic. The structures of compounds prepared were confirmed via elemental analyses, IR, 1H-NMR and mass spectra. Four types of angular 1:1 hydrogen-bonded supramolecular complexes were prepared via hydrogen-bond formation between each of the pyridine-based derivatives and two types of benzoic acids, namely, 4-alkoxy and 4-substituted benzoic acids. The latter bear the polar groups (CH3O, CH3, Br and NO2) in addition to benzoic acid. Complexes were similarly investigated and it was found that three of them are mesomorphic while the fourth is not. The formation of 1:1 hydrogen-bonded supramolecular liquid crystals complexes was confirmed by FTIR spectroscopy.