Uv Stability of High Birefirngence Liquid Crystals

High birefringence (Dn 0.4) liquid crystals (LCs) are desirable for cholesteric displays, laser beam steering and optical switches for telecommunications [1]. A major concern for the high birefringence LCs is their ultraviolet (UV) stability. As the conjugation length increases, the LC absorption tail shifts toward k 1⁄4 365 nm, the major UV light used for curing sealant. The material degradation is believed to originate from the UV-induced free radicals which, in turn, trigger chemical reactions with neighboring molecules and then disturb the LC alignment. When a LC cell is deteriorated by the accumulated UV exposure, the threshold voltage is smeared, birefringence decreased, viscosity increased and light scattering intensified [2].