Mesomorphism and flexibility of alkyl chains in chalcone esters.

A novel homologous series of chalconyl ester liquid crystals (LCs): RO−C6H4–CH:CH–COO−C6H4–CO−CH:CH−C6H4–OC10H21(n) (para) has been synthesized and studied with a view to understanding and establishing the relationship between molecular structure and LC properties with reference to flexibility of the terminal chain. The novel series consists of eleven homologs (C1–C16). The C1and C2homologs are nonliquid crystals and the rest of the homologs (C3–C16) are enantiotropic nematic without exhibition of smectic mesophase. Transition and melting temperatures were determined by an optical polarizing microscope equipped with a heating stage. Textures of nematic phases are threaded or Schlieren. Cr-N/I transition curve adopts a zigzag path in a normal manner with overall descending behaviors. The N-I transition curve exhibits a sharp and shorter odd-even effect from C3to C6and it diminishes from and beyond C6for higher homologs of longern-alkyl chain (R) in more or less or negligible deviating manner from normal descending tendency. Thermal stability for the nematic is 116.4°C and mesophase length ranges from 19°C to 67°C at the C3and C12homolog respectively. The LC properties of present novel series are compared with structurally similar analogous series to derive group efficiency order. [ABSTRACT FROM PUBLISHER]