Polar order of an achiral taper-shaped liquid crystal in the uniaxial smectic A phase

Abstract

We prepared an achiral taper-shaped liquid crystal in which cyanobiphenyl, phenylpyrimidine, and 1,4-diphenyl-2,3-difluorobenzene units are connected to 2,4-dihydroxybenzoic acid via flexible spacers. We then investigated its liquid-crystalline properties using polarized optical microscopy, differential scanning microscopy, and X-ray diffraction. The compound was found to exhibit an intercalated smectic A phase. An electro-optical switching accompanying a ferroelectric-type polarization peak was observed in the SmA phase. There is a single peak per half-cycle, which is delayed with respect to the zero-crossing point of the applied electric field. The electric response appears when the applied field is larger than a certain value. Therefore, the electric response is attributed to the electric-field induced polarization. The polar switching is explained in terms of the existence of polar smectic clusters in which the molecules organize in a head-to-tail alignment. Coupling of a taper-shaped structure and phenylpyrimidine–cyanobiphenyl interaction organizes a polar order parallel to the layer normal in the SmA phase.