Color change effect based on provitamin D phototransformation in cholesteric liquid crystalline mixtures

It has been shown that UV radiation can produce observable color changes in induced cholesteric systems ( nematic + optically active dopant) additionally doped with ergosterol ( provitamin D-2). The effect is based on the photoinduced conversion of ergosterol into vitamin D-2, which has the opposite sign of its helical twisting power. The observed shifts of the selective reflection peaks ( more then 100nm after 10 min of UV irradiation) allow both instrumental and visual monitoring of biologically active UV radiation.