Dependence of Molecular Flexibility of Lateral Group on Mesomorphism

A Chalconyl homologous series: RO-C6H4-CH=CH-CO-C6H4-OC12H25(n) (meta) of novel liquid crystalline (LC) derivatives of thermotropic variety have been synthesized and studied with a view to understand the effect of molecular structure on LC behaviours with reference to varying flexibility due to tailed end group for the same homologue and from homologue to homologue in the same series. A novel series consisted of thirteen homologues whose first member is nonliquidcrystals and the rest of the homologues are LC in enantiotropic or monotropic condition. Nematogenic mesomorphism commences from C2 homologue. C2 to C5 homologues are enantiotropic nematic and C6 to C18 homologues are monotropic nematic. Smectogenic character commences from C4 homologue as enantiotropic manner and C6 to C18 derivatives are monotroic smectic. Transition temperatures and textures of mesophases were determined by an optical polarising microscopy (POM) equipped with a heating stage. The transition curves of a phase diagram behaved in normal manner. Spectral, analytical and thermal data supported the molecular structures of homologues. Thermal stability for smectic is low of the order of 56.0 °C and that of the nematic is 70.5 °C. The corresponding mesophaselengths for smectic and nematic are varied minimum to maximum are 1 or 2 °C to 15 °C and 5 to 29 °C respectively. The group efficiency order derived on the basis of thermal stability .