ANTIFERROELECTRICITY AND CHIRAL ORDER IN NEW LIQUID-CRYSTALS OF NONCHIRAL MOLECULES STUDIED BY OPTICAL 2ND-HARMONIC GENERATION

Several homologs of new liquid crystals of strongly bent, achiral mole cules have been investigated by optical second harmonic generation. It is shown that the initial nonpolar mesophase is converted into a pola r state, which leads to frequency doubling of optical waves by applyin g electric fields of a few V/mu m. The observed symmetry breaking is e xplained by a field-induced antiferroelectric to ferroelectric transit ion. The symmetry group and nonlinear coefficients as large as d(31) = 16 pm/V have been determined for the field-induced state from polariz ation and angle-dependent measurements.