Photochemical and Thermal Stability Studies on a Liquid Crystal Mixture of Cyanobiphenyls

Abstract

Liquid crystals (LCs) have unique properties that allow them to be used in information display devices.1 In particular, LCs are useful for displays used in wrist watches, calculators, message boards, flat-panel television, and large-screen projection systems.2 The choice of materials is often dictated by the desired application. The use of LCs in electro-optical devices exposed to high-intensity light must meet not only the usual criteria for these devices such as birefringence, dielectric and conductivity anisotropy, and alignment qualities, but must be photochemically stable to long exposures of visible light and thermally stable to heat generated by exposure to visible and near infrared light. Large-screen projection displays that use liquid crystal light valves3 have more severe photochemical stability requirements to achieve long lifetime displays than many other devices. Even very small absorption “tails” of the LCs that extend into the visible region of the spectrum can cause lifetime problems (should photo-decomposition occur) because of the high intensity of light used. Figure 1 shows a light valve projection system.3