TGB_A phase in chiral two ring derivatives

Abstract

New chiral compounds with two benzene ring derivatives have been synthesized and studied. The helical S_A* phase (TGB_A phase) has been found in the long alkyloxy chains and proved by different techniques: optical textures, contact method, racemic mixtures and pitch measurement. The latter was also performed in ferroelectric S_C* phase. The helical pitch increases from 0.65μm to 1.3μm with decreasing temperature in the TGB_A phase of the hexadecyloxy derivative; in the S_C* phase, the pitch is very short: it augments from 0.2μm to 0.28μm when the temperature increases, and suddently drops down to 0.21μm near the S_C*-TGB_A transition. Electro-optical properties of the S_C* phase were studied with classical SSFLC geometry. The dielectric measurements detect a relaxation process in the TGB phase. The temperature dependences of the dielectric strength and the critical frequency are similar to those of the corresponding “soft mode” relaxation process classically observed in the S_A phase close to the transition.