STUDIES OF THE AGGREGATION OF A NEW BENZIMIDAZOLON-AMINO-ANTHRAQUINONE DYE IN WATER-DIOXANE MIXTURES

This visible absorption spectra of a new benzimidazolone-amino-anthraq uinone dye in water-dioxane mixtures were obtained. The benzimidazolon e-anthraquinone dye investigated is sodium salt of mino-benzimidazolon e-2')-anthraquinone-2-sulphonic acid. In the spectra of the dye in the mixtures containing less than 60% dioxane, the absorption was found t o increase with increase in the dioxane content. This spectral change was attributed to the decrease in the tendency of the dye to aggregate . In the spectra of the dye in the mixtures containing more than 70% d ioxane, however, the absorption was found to decrease with an increase in the dioxane content, i.e., with a reduction in the dielectric cons tant of the solvent. This spectral change was considered to be charact eristic of the increase in the electrostatic interaction between the d ye ion and the counter ion.