Supramolecular liquid crystals in binary and ternary systems

Abstract

Five, new laterally methyl-substituted, pyridine-based derivatives ( I8– I16) having molecular formula 4-C n H 2 n+1 O–C 6H 4COOC 6H 3(2-CH 3)–N N–C 5H 4N, with n varies between 8 and 16 carbons, were prepared and investigated for their mesophase behavior by differential scanning calorimetry (DSC) and polarized light microscopy (PLM). All prepared homologues were found to be smectogenic, possessing the smectic C mesophase. Binary mixtures, covering the whole concentration range, were independently prepared from corresponding isomers, one from series I n and the other from series II n, in which the methyl group is introduced this time into position-3. All mixtures were similarly characterized and their binary-phase diagrams constructed, from which the eutectic composition of each pair of isomers was determined. The increased stability of the SmC phase of mixtures is a consequence of the enhanced lateral molecular forces between the two components of the mixture. Hydrogen-bonded 1:1 associates, formed between each of the derivatives ( I8– I16) and 4-alkoxybenzoic acids ( III m), were prepared and similarly characterized to investigate the effect of lateral methyl orientations on the stability of the mesophases induced by intermolecular hydrogen bonding. All complexes prepared were investigated for their mesophase behavior by DSC and PLM and found to possess SmC as the only mesophase observed. The formation of the hydrogen-bonded complexes was confirmed by constructing their binary phase diagrams with the acid that cover the whole range of concentration of the two complements. Finally, the formation of the hydrogen-bonded complexes between the eutectic mixtures of two pyridine-based isomers ( I/ II) and 4-alkoxybenzoic acids ( III m) was confirmed by constructing their apparent binary phase diagrams (actually of three components) with the acid ( III) that cover the whole range of concentration of the two components (eutectic I/ II and III).