New Liquid Crystalline Compounds Involving Ester-Chalcone Linkages Having 1,3,5-Trisubstituted Pyrazole as a Terminal Group

Abstract

Mesogens with chalcone central linkage are rare. It has been observed that –CO–CH=CH– linkage is less conducive to mesomorphism compared to –CH=N– (azomethine), –COO– (ester), –N=N–(azo) linkages due to the non linearity and angle strain arising from the keto group. But when –CO–CH=CH– linkage is present with other central linkages it becomes condusive to mesomorphism. In the present investigation two homologous series were synthesized having chalcone as a one of the central linkage. The homologous series have been derived from 1,3,5-trisubstituted pyrazole, p-hydroxy acetophenone, and alkoxy acid. Viz. 4(4′-n-alkoxybenzoloxy) phenyl-propane-3-one(1-phenyl-3-methyl-2-pyrazoline-5-one) [series-I] and 4(4′-n-alkoxybenzoloxy) phenyl-propane-3-one(1-phenyl(4″-methyl)-3-methyl-2-pyrazoline-5-one) [series-II]. The compounds of the both series have been characterized by elemental analyses, FT-IR, 1H-NMR, and Mass spectrometry methods. Their liquid crystalline properties have been investigated by optical polarizing microscopy and DSC studies. All the derivatives are mesomorphic in nature. C1 to C5 of both the series exhibit only nematic phase. C6 to C8 in series-I and C7 & C8 in series-II exhibit smectic as well as nematic phase. Whereas C10–C16 in series-I and C8–C16 in series-II showing only smectic phase.