Helical twisting in nemato-cholesteric systems based on cholesterol derivatives and photosensitive azoxy compounds

Abstract

For cholesteric liquid crystal systems containing photosensitive nematic ZhK�440 and a mixture of cholesterol derivatives, changes in helical twisting induced by UV radiation were studied. The UVinduced shift of selective reflection maximum λ max was shown to depend upon concentration of the nematic compo� nent. For low concentrations of ZhK�440, λmax increases, which correlates with corresponding changes with increasing temperature. For higher concentrations, λmax decreases, regardless of the temperature behavior of the system. A theoretical description of the available experimental data is proposed on the basis of develop� ment of molecular models of helical twisting, including an assumed possibility of ordered orientation of short molecular axes of cisisomers formed as a result of UV irradiatio n, which is determined by the sense of the cholesteric helix already present in the system.