Aroylhydrazone appended cinnamate based calamitic liquid crystal:Effect of alkoxy side chain and position of terminal pyridine core on mesomorphic properties

Abstract

Eight newly synthesized liquid crystalline materials containing aroylhydrazone and cinnamate linking units, connected by three phenyl rings and flexible alkoxy side chains, were designed and synthesized. The confirmation of their structures was characterized by using FT-IR, 1H NMR, and 13C NMR, and elemental analysis. The phase behavior of these materials was investigated using crossed polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction techniques. Additionally, their thermal stability was assessed using thermo gravimetric analysis. In the two series of materials studied, those with shorter alkoxy side chains exhibited a smectic C phase along with a nematic mesophase, while compounds with longer alkoxy chains showed only smectic A type mesogenic behavior. The structure-property relationship of these aroylhydrazone-based homologous series was discussed to understand the impact of side alkoxy tail length and the position of the terminal isonicotinic/nicotinic hydrazide core on the liquid crystalline properties. All four materials displayed a wide temperature range of mesophases and exhibited high thermal stability. To gain further insights into their mesomorphic properties, we employed density functional theory to conduct theoretical calculations on various structural and chemical parameters of these materials, including reactivity, energy bad gap, and dipole moment.