Light-controlled electro-optic response in a ferroelectric liquid crystal with sign reversal of the spontaneous polarization P sub(S)

At fixed polarity, the direction of molecular switching in ferroelectric liquid crystals, and hence the sign of electro-optic response, depends on the sign of P sub(S). Here, we present a light-controlled electro-optic response of a ferroelectric liquid crystal mixture consisting of a single component ferroelectric host, that exhibits a sign reversal of P sub(S) with temperature, and a small amount of azo dye. It was found that, due to photoisomerisation of the azo dye, the sign reversal temperature of P sub(S) (T sub(rev)) increased upon UV illumination. As consequence, if the mixture was illuminated at temperature several degrees above T sub(rev), the electro-optic response reversed its sign. This effect seems to be applicable in light-controlled liquid crystal light switches.