Photoferroelectric smectic-C* liquid crystal mixtures

Homogeneous mixtures of photoisomerizable azobenzene dyes with smectic-C* ( SmC* ferroelectric liquid crystals (FLCs) are photoresponsive ferroelectric s photoferroelectrics) where the trans-to-cis photoisomerization of the azo benzene molecules result in a pronounced modulation of the ferroelectric pr operties. FLCs with high photoresponse of the spontaneous polarization had been obtained by dissolving small amounts of azobenzene dyes in the ferroel ectric SmC* host phase FLC 6430. In the absence of light the properties of the mixtures are not significantly different from those of the pure host ph ase. Irradiation with light of appropriate wavelength considerably reduces the spontaneous polarization of these mixtures. After removal of the light source, the initial dark value is reversibly recovered by thermal cis-to-tr ans reisomerization. Time-resolved measurements are discussed with respect to the dynamics of these photoinduced changes.