Synthesis, Mesophase Behavior and Thermal Stability of Liquid Crystals Based on Different Central Linkages with Lateral Substitution and Terminal Heterocyclic Moieties

Abstract

The synthesis and evaluation of thermal behavior of two new mesogenic homologous series of liquid crystalline compound containing 1,2,4-triazole and isonicotinic acid ring at the terminus of the molecule have been reported, viz. 3-hydroxy-4-[(4-1,2,4-triazol-4-ylimino)methyl] phenyl 4-alkoxybenzoate (Series-I) and 3-hydroxy-4 (isonicotinoyl carbonohydrazonoyl) phenyl 4-alkoxy benzoate (Series-II). The compounds of both the series have been characterized by elemental Analysis, FT-IR, mass spectrometry, 1H-NMR and 13C-NMR. Phase transition temperatures and the thermal parameters were obtained from differential scanning calarimetry (DSC). The texture observation was performed under polarizing optical microscopy (PMO) attached with Mettler hot stage. All the derivatives are mesomorphic in nature showing nematic phase as well as higher members of both the series show smectic phase. The use of triazole and isonicotinic acid as a terminal group has a very dramatic effect on the melting and clearing points. Similarly lateral –OH substitution on central phenyl ring shows higher clearing temperature due to intermolecular hydrogen bonding. The mesomorphic behavior has been analyzed in terms of structural property relation.