Solvatochromism, Preferential Solvation and Multiparametric Approach to the Spectral Shift of Methyl Orange in Aqueous Cosolvent Mixtures

In this study, the solvatochromic behavior of Methyl orange was studied visible spectrophotometrically in seven aqueous binary systems from water with methanol, ethanol, propanol, DMF, DMSO, acetone and dioxane solvents. The spectral data was interpreted in terms of solute-solvent and solvent-solvent interactions. The deviation from linearity in the plots of & nu;(max) versus x(2) due to preferential solvation of the Methyl orange by one component of the mixed solvent and due to solvent microheterogeneity. The preferential solvation parameters local mole fraction X-2(L), solvation index & delta;(s2) and exchange constant K-12 were evaluated. The preference of solute to be solvated by one of the solvating species relative to others was explained. All values of K-12 were less than unity that indicates the preferential solvation of Methyl orange by water, except in case the water-propanol mixture where K-12 was higher than unity. The preferential solvation index & delta;(s2) values were calculated and interpreted for each binary mixture. The magnitude of preferential solvation index was highest in water-DMSO mixtures than in the all other solvent mixtures. The energy of electronic transition in maximum absorption (E-T) was calculated in each binary mixture. The extent and importance of each solute-solvent interactions to E-T were analyzed by the linear solvation energy relationships using the Kamlet-Taft strategy.