Synthesis and Liquid Crystalline Properties of Novel Ethylene Derivatives

Abstract

A novel homologous series of liquid crystals, viz., α-4-[4′-n-alkoxy cinnamoyloxy] benzoyl -β-4″-chloro phenyl ethylenes, has been synthesized. The series consists of twelve homologs. The methyl to butyl derivatives are not liquid crystalline and the rest of the homologs are enantiotropic liquid crystals. The octyl to dodecyl derivatives of the series are enantiotropically smectogenic in addition to nematogenic in character, but the pentyl, hexyl, heptyl tetradecyl, and hexadecyl homolog derivatives of the series are only nematogenic without the exhibition of a smectic phase. The transition temperatures of the novel substances were determined by optical polarizing microscopy equipped with a heating stage. A plot of transition temperatures versus the number of carbon atoms present in the n-alkoxy terminal chain represents the phase behavior of the series. An odd-even effect is observed for the nematic-isotropic transition curve. The textures of the nematic phase are of a threaded or Schlieren type and those of the smectic A and smectic C phases are typical. Analytical and spectral data agree with the molecular structures. The smectic and nematic thermal stabilities are 132.6°C and 156.7°C, respectively. The smectic phase commences from the octyloxy homolog. Smectogenic phase lengths vary from 26°C to 33°C and the nematogenic phase lengths vary from 6°C to 70°C. The series is predominantly nematogenic and partly smectogenic with considerable mesophase length and a middle-ordered melting type. The liquid crystal properties of the present series are compared with structurally similar homologous series.