Generation of biaxiality in smectic A phases by introduction of intermolecular perfluoroarene–arene and C–H/F interactions, and the non-odd–even effect of the molecules in their transition temperatures and layer distances

Abstract

Compounds 1a–j, 4-alkoxy-4′-pentafluorobenzoyloxybiphenyls, were synthesized to investigate the biaxiality in the smectic A phases of rod-like molecules possessing both perfluorinated and non-fluorinated benzene rings. The phase behaviors of the compounds and the molecular packing structures of their smectic A phases were investigated by polarized optical microscopy (POM), differential scanning colorimetry (DSC), and X-ray diffraction (XRD). As a result, it was found that the plot of the transition temperatures against the number of carbon atoms in the terminal alkyl chains did not show a clear odd–even effect, and an unique effect “tgg-effect” was observed in the plots of their layer distances against the number of carbon atoms. In the detailed 1D- and 2D-XRD studies of the smectic A phases, lateral directional orders in each layer were observed. It is assumed that these results originate from the biaxiality of the smectic A phases and slow rotation of the molecules around their molecular long axes.