Solvent effects on the spectroscopic properties of triarylmethane dyes

The spectroscopic characteristics of two highly symmetric triarylmethane dy es, Crystal Violet and Ethyl Violet, and two triarylmethanes displaying low er symmetry, Victoria Blue R and Victoria Pure Blue BO, were investigated i n a variety of polar solvents. The solvent effects observed on the electron ic spectra of the highly symmetric dyes add momentum to previous objections to the rotamers model, a model traditionally used to explain the appearanc e of a shoulder in the short-wavelength side of the maximum absorption band of Crystal Violet in ethanol. We have found that, in polar solvents the ma gnitude of the splitting between the overlapped absorption bands of Crystal Violet is dependent on the solvatochromic properties of the media. The nat ure of this dependence suggested the existence of specific interactions bet ween Crystal Violet and the surrounding solvent molecules. We hypothesize t hat these solute-solvent interactions represent the symmetry-breaking event that lowers the symmetry of Crystal Violet in solution, and gives rise to the appearance of the spectroscopic shoulder at the short-wavelength side o f its maximum absorption band. Analogous results were obtained for Ethyl Vi olet. The solvent effects observed on the absorption spectra of the triaryl methanes displaying lower symmetry were different from those observed for t he highly symmetrical compounds. This difference was rationalized in terms of the distinct nature of the overlapping absorption bands characteristic o f these two distinct sets of dyes. (C) 2000 Elsevier Science Ltd. All right s reserved.