Anthraquinone Liquid crystal dichroic dyes – a new form of chromonic dye?

Dichroic dyes, based on anthraquinone chromophores, for incorporation into various liquid-crystalline host mixtures have been prepared. For each dye, which has been designed to absorb at different regions of the visible spectrum, we investigate liquid crystalline behaviour and prepare mixtures of dyes that also promote liquid-crystalline behaviour. The 2,6-disubstituted dyes, which are yellow and red, respectively, exhibit nematic and smectic C phase behaviour or smectic A and E phase behaviour over wide temperature ranges. In order to produce blue dyes we report a family of dyes derived from 1,5-dihydroxy-4,8-dinitroanthraquinone, which is similar in structure to known chromonic dyes. These dyes exhibit unusual optical textures by polarised optical microscopy, and display unusual mixing behaviour, which suggests the presence of a new type of liquid crystal.