PREFERENTIAL SOLVATION OF SOLVATOCHROMIC BENZOTHIAZOLINIC MEROCYANINES IN MIXED BINARY SOLVENTS

The preferential solvation of alpha- and gamma-oxobenzothiazolinic mer ocyanines was studied using UV-visible spectroscopy in binary solvent mixtures containing either water or methanol and cosolvents (formamide , ethanol, 2-propanol, DMF, CH,CN and 1,4-dioxane). In binary mixtures containing water, the dyes are preferentially solvated by the organic cosolvent over the whole composition range, only in the case of the a lpha-oxo derivative in H2O-CH3CN mixtures the solvatochromic plot show ed a biphasic behavior. In binary solvent mixtures comprising MeOH, th e dyes showed no preference for either solvents in MeOH-EtOH mixtures, while in MeOH-CH3CN and 1,4-dioxane-MeOH mixtures the former solvent was the preferred one. Also, the results showed that gamma-oxo derivat ive is preferentially solvated by the cosolvent in both MeOH-2-propano l and MeOH-DMF mixtures. Although the alpha-oxo analogue showed an ide al behavior in MeOH-2-propanol mixtures as well as in the MeOH rich re gion in MeOH-DMF mixtures, it is solvated preferentially by MeOH in th e DMF rich side. Also, the role of solute-solvent and solvent-solvent interactions in determining the preferential solvation was discussed. (C) 1998 Elsevier Science B.V. All rights reserved.