Mesomorphism dependence on geometric shapes in isomeric molecules

Abstract

ABSTRACTA novel homologous series of symmetrical dimers RO-C6H4-CH˭CH-COO-C6H4-OOC-CH˭CH-C6H4-OR of liquid crystalline (LC) characteristics have been synthesized and studied with a view to understand and establish the effects of the molecular structure on the LC property or properties with special reference to geometrical shape in case of isomeric series. Homologous series consisted of 13 dimers (C1 to C18). C1 to C8 are only enantiotropic nematic and the rest of the dimer homologues from C10 to C18 are enantiotropically smectogenic in addition to nematogenic. Textures of the nematic phase are threaded or Schlieren and that of the smectic phase are of the type smectic A or C. Transition temperatures and the textures were determined by an optical polarizing microscopy equipped with a heating stage. Thermal stability for smectic and nematic are 161.0 °C and 237.6 °C, respectively, whose total mesophase (Sm+N) length ranges from 71.0 °C to 126.0 °C. Cr–M, Sm–N, and N–I transition curves of a phase diagram behaved in normal manner except negligible abnormality at C14 dimer of N–I transition curve. N–I transition curve exhibited odd– even effect nearby up to C7 dimer. Analytical and spectral data supported molecular structures of homologue dimers. Thus, present homologue dimer series is predominantly nematogenic and partly smectogenic and high-ordered melting type. LC properties of present novel series are compared with structurally similar series.