The molecular structures and properties of anthraquinone-type dichroic dyes

Relations between the molecular structures and properties of anthraquinone- type dichroic dyes were studied. Newly developed asymmetric dyes with thiop henyl groups are highly soluble in fluorinated liquid crystals and the dich roic ratios of these dyes are high (about 10). However, ortho-position (thi ophenyl)-substituted dyes have lower solubilities and dichroic ratios than other position-substituted dyes. The properties of anthraquinone dyes with anilino groups are much lower than those of dyes with thiophenyl groups. Th ese results can be strongly related to the flexibility of substituents. We newly established a hypothesis concerning dyes in liquid crystal solvent. I n liquid crystals, the dye has a suitable conformation to adjust to liquid crystal phase. In this conformation, the solubilities and dichroic ratios a re increased because the interactions between the dye molecules and liquid crystal molecules are strengthened. Flexible substituents are considered to easily form a suitable conformation and realize excellent properties.