Synthesis and study of liquid crystalline properties of schiff’s bases having 1,3,4-thiadiazole moiety

Abstract

A new homologous series of Schiff’s bases derived from substituted 2-amino 1,3,4-thiadiazole has been synthesised and their liquid crystalline properties investigated by Polarising Optical Microscope and Differential Scanning Calorimetry. Thirteen homologues were synthesised by condensing substituted 4-n-alkoxy benzoyloxy benzaldehydes with substituted 2-amino 1,3,4-thiadiazole. The methyl to n-hexyl derivatives exhibit only nematic phases. The n-heptyl to n-octadecyl derivatives exhibit smectic and nematic phases. The plot of transition temperatures versus number of carbon atoms in the alkoxy chain exhibits falling tendency for nematic–isotropic transition temperatures and rising tendency for smectic–nematic transition temperatures. The mesomorphic and thermal stability is compared with other homologous series. The result indicates that ester linkage enhances smectic thermal stability but decreases nematic thermal stability. The enhancement in smectic phase is much higher. Compounds are characterised by IR spectral data, NMR, DSC and microscopic study.