Study of mesomorphism and its relation to molecular structure through molecular rigidity and flexibility.

Novel liquid Crystalline (LC) substances of chalconyl ester derivatives from Vinyl aromatic carboxylic acids are synthesized and studied with a view to understanding and establishing the relation between molecular structure, RO-C6H4-CH=CH-COO-C6H4-CH=CH-CO-C6H4-F (para) and LC properties of the thermotropic variety. Homologous series consists of eleven members (C1to C16). C1and C2members of novel series are nonliquid crystals (NLC) and the rest of the homologues (C3to C16) are enantiotropic nematic with absence of smectic property throughout. Transition temperatures and textures of homologues were determined by an optical polarizing microscope (POM) equipped with a heating stage. Textures of nematic phase are threaded or Schlieren. The transition temperatures of novel homologues are relatively lower than the corresponding dimeric trans n-Alkoxy Cinnamic acids from which, novel homologues are synthesized. Thermal, analytical, spectral data confirmed molecular structures of novel homologues. Cr-N/I and N-I transition curves behaved in normal manner except C8to C14homologues which deviated from normal descending tendency in N-I transition curve. N-I transition curve exhibited odd-even effect up to C6homologue and odd member's N-I transition curve occupied lower position than even member's N-I transition curve. Thermal stability for nematic is 118.2°C; with its total mesophase length ranging from 12.0 to 50.0°C. Thus, it is a middle ordered melting type series with absence of smectic property. Group efficiency order derived on the basis of thermal stability using comparative study of present novel series with structurally similar analogous series as mentioned below. Smectic: Series-Y > Series- X = Series-1 and Nematic: Series-X > Series- 1 > Series-Y [ABSTRACT FROM AUTHOR]