Mesogens Based on Cholesterol Derivatives: Synthesis and Characterization

Abstract

A new series of liquid crystals involving cholesterol based mesogenic units and Schiff base moiety interlinked through ester linkage were designed and synthesized. The target compounds were obtained by the reaction of 4′-(3-cholesteryl oxy carbonyl)benzaldehyde with different substituted aromatic and heterocyclic amines. The molecular structures of the compounds were confirmed by Fourier transform infrared (FT-IR), 1H, and 13C nuclear magnetic resonance spectra. The mode of linkage has been made via ‒COO‒ and ‒C˭N‒ bonds. The linkages and different substituted aromatic and heterocyclic groups were undertaken to study their influence on the isotropization temperature (Ti) and on mesomorphic property. The thermal phase behavior of the synthesized compounds was investigated by polarizing optical microscopy coupled with hot stage and differential scanning calorimetry (DSC). Enantiotropic cholesteric phase were shown by 4′-[3-Cholesteryloxycarbonyl]benzylidene- 1, 2, 4- triazine-3-yl and monotropic nematic mesophase were shown by 4′-[3-Cholesteryl oxycarbonyl]benzylidene-(4- methyl)aniline whereas 4′-[3-Cholesteryloxycarbonyl] benzylidene-(4-butoxycarbonyl)aniline defined oily streak phase in heating cycle. The remaining members of the series exhibited monotropic droplet texture in cooling cycle with exclusive suppression of cholesteric phase.