Correlations among molecular structures, solubilities in fluorinated media, thermal properties and absorption spectra of anthraquinone dichroic dyes with phenylthio and/or anilino groups

Abstract

Attractive correlations among molecular structures, solubilities in fluorinated media, thermal properties and absorption spectra of several anthraquinone dichroic dyes with phenylthio and/or anilino groups were investigated. These dyes are classifiable into three types from the viewpoint of correlations between thermal properties and solubilities. The first group consists of hardly soluble anthraquinone dyes with the same phenylthio groups at positions 1 and 5. They have large enthalpy of fusions (94–127 kg/kJ) which induce strong interactions among dye molecules. The second group consists of dyes with two different phenylthio groups at positions 1 and 5. They have smaller enthalpy of fusions (around 60 kg/kJ) and can be solved in the cases of some combinations of phenylthio groups. The third group consists of dyes with two different phenylthio groups and one of them has a trifluoromethyl group at a meta position. They have very low enthalpy of fusions (2.8–22.8 kg/kJ) and their solubilities are very large even at low temperatures. The difference between the solubility in fluorinated liquid crystals and in fluorinated solvents suggests that dyes in liquid crystal phase have specific solvation forms that are different from those in isotropic phase.