Liquid Crystalline Materials

Liquid crystal materials (LCM) for guest-host liquid crystal displays differ from common LCM only in that they additionally contain one or more dichroic dyes. However, the introduction of dichroic dyes (DD) in LCM must not result in deterioration of the operational characteristics such as conductivity or chemical, photochemical, and thermal stabilities, or a change in the phase transition temperature. In order to obtain good contrast in the guest-host electrooptical devices, the concentration of the dye in the liquid crystal must be chosen such that it ensures the necessary optical density of the solution in the long-wave absorption band, D =1.5, for the layer thickness of 5 to 10 µm. The problem of producing DD with suitable solubility in liquid crystals remained unsolved for many years. Azo and anthraquinone dyes and their mixtures have been obtained whose solubility is sufficient for practical application.