Dielectric studies on two isomeric cyano ester homologous series

Abstract

We have studied the static dielectric permittivities of two homologous series of compounds, viz., 4-cyanophenyl 4'-n-alkoxybenzoates (CPnOB) and 4-n-alkoxyphenyl 4'-cyanobenzoates (nOPCB). These are biaromatic compounds with a terminal cyano group, but the ester linkages in the two series are oppositely disposed. For both series of compounds, the mean permittivity shows a jump at the nematic-isotropic transition that increases with increasing chain length. The pretransitional effects in the isotropic phases of the compounds CPnOB, wherein the longitudinal component of the dipole moment of the ester linkage is additive with regard to the cyano end-group, are found to be nearly one order of magnitude larger than those seen in the case of the nOPCB compounds.