Smectic Liquid Crystal Imaging Devices Based on a Photochemical Reaction

Irradiation by ultraviolet or visible light is found to induce a reversible change in the phase transition temperatures of smectic liquid crystals doped with an isomeric compound such as azobenzene. Such irradiation is also found to bring about a reversible change in the threshold voltage for electrohydrodynamic instability and in the electro-optical and thermo-optical characteristics by a photochemical trans (cis)-cis(trans) isomerization. Some experimental results are described for two types of cell; one includes a small amount of electrolyte and the other includes a cholesteric liquid crystal, in addition to the isomeric compound. Some novel imaging devices based on the effects are also proposed, in which an ultraviolet image is converted to a visual image with high contrast and a long-term memory.