Study of the Effects of Decreasing Molecular Rigidity on Mesomorphism

Abstract

A Chalconyl homologous series: RO-C6H4-CH=CH-CO-C6H4-OC14H29(n) (meta) is synthesized and studied with a view to understand and establish the effect of molecular structure on Liquid crystal behaviour by reducing molecular rigidity through diminishing of a phenyl ring and a central carboxy or vinyl carboxy group from a molecule. Novel series consists of thirteen homologues (C1to C18). First member (C1) homologue is nonliquid crystal and the rest of the homologues (C2to C18) are enantiotropically ( C2to C5) nematogenic or monotropically (C6to C18) nematogenic plus smectogenic of low mesophaselengths and low transition temperatures ( 38°C to 76°C). Transition temperatures were determined by an optical polarizing microscopy (POM) equipped with a heating stage. Cr-N/I, N-I, I-N, N-Sm transition curves behaved in normal manner in a phase diagram. N-I and I-Sm transition curves exhibited odd-even effect. Textures of nematic phase are threaded or schlieren and that of the smectic phase are of the type A or C. Analytical, spectral and thermal data supported molecular structure of homologues. Thermal stability ( N-I/ I-N) of series for nematic is 67.5°C and that of the smectic is very low. Group efficiency order derived on the basis of thermal stability is as under. –Cl with –C6H4.COO- > -OC14H29(n) without –C6H4.COO-with reference to central bridge –CH=CH-CO-.