Dependence of Mesomorphism on meta Substituted Lateral Groups

Thermotropic LC substances of chalconyl derivatives consisting of two phenyl rings, one chalconyl central bridge and two flexible {-OR and -OC7H15(n)} terminal (para) / lateral (meta) functional groups i.e. RO-C6H4-CH=CH-CO-C6H4-OC7H15(n) (meta) have been synthesized and studied for the effect of molecular structure on thermotropicmesomorphism. The thermometric behaviours of novel homologue substances and their textures were determined by an optical polarizing microscopy (POM) equipped with a heating stage. Textures of a nematic phases are threaded or schlieren. The textures of monotropicsmectic phase are directly judged from the heating top as smectic-A. Analytical, thermal and spectral data supports and conforms the molecular structures of homologues. Transition curves as depicted in a phase diagram behaves in normal manner. Odd-even effect for N-I transition curve (very short) is observed. Total (C1 to C18) thirteen homologues are synthesized .Mesomorphism commences from C7 homologue. C7 to C8 homologues are enantiotropicnematic and C10 to C18 homologues are monotropicllynematogenic plus smectogenic. Thermal stability of smectic phase is about fraction of 1.0 °C or 1.0 °C and that of nematic phase is 66.0 °C with total mesophaselength minimum to maximum 7.0 °C to 15 °C. Group efficiency order for mesophases is derived on the basis of thermal stabilities from the comparative study of thermometric data determined from structurally analogous series. Hence present novel series behaves in normal manner with very short mesophaselengths, low thermal stabilities and low melting type and predominantly nematogenic and partly smectogenic.