Achiral straight-rod liquid crystals indicating local biaxiality and ferroelectric switching behavior in the smectic A and nematic phases

Abstract

Biaxial smectic A (SmA_b) and biaxial nematic (N_b) liquid crystal (LC) phases using achiral straight-rod molecules were realized through perfluoroarene–arene (PFA–A) and CH/F interactions. Compounds 1a, 1b and 1c, 4,4′-bis(2,3,4-trifluorobenzoyloxy)biphenyl, 4,4′-bis(2,3-difluorobenzoyloxy)biphenyl and 4,4′-bis(2-fluorobenzoyloxy)biphenyl, were synthesized. The liquid crystallinity of these compounds was investigated using polarized light optical microscopy (POM) and differential scanning calorimetry (DSC). Furthermore, the ferroelectric switching behaviors of 1a in the nematic (N) and smectic A (SmA) LC phases and 1b in the N phase were confirmed by applying a triangular wave voltage in electro-optic experiments. Then, the values of spontaneous polarization (P_s) in the LC phases of 1a were investigated as functions of frequency, voltage, and temperature. It was strongly hypothesized that the semiperfluorinated phenyl (SFP) groups rotate around the molecular long axes and change pairs in the CH/F interacting sites, and this cooperative movement of the SFP groups is repeated during the switching process.