Preferential solvation and behavior of solvatochromic indicators in mixtures of an ionic liquid with some molecular solvents.

Structural and intermolecular interactions of solvatochromic probes 4-nitroaniline, 4-nitroanisole, and Reichardt's dye were investigated in the binary mixtures of 2-hydroxy ethylammonium formate as an ionic liquid with N,N-dimethyl formamide, dimethyl amine, and dimethyl sulfoxide. Solvatochromic parameters (ETN, normalized polarity parameter; pi*, dipolarity/polarizability; beta, hydrogen-bond acceptor basicity; alpha, hydrogen -bond donor acidity) were determined in ionic liquid mixtures at 25 degrees C using UV-vis spectroscopy. ETN parameters obtained from absorbance of Reichardt's dye within various mixtures of ionic liquid were observed to be higher than predicted values from ideal additive behavior. Synergistic solvation behavior for some mixtures was observed. The combined nearly ideal binary solvent/Redlich-Kister (CNIBS/R-K) equation was used for various parameters correlation to predict solvatochromic parameters. Preferential solvation model was applied for the first time in the ionic liquid mixtures to study solvent mixtures effects on solvation of indicators, and from these information solute-solvent and solvent-solvent interactions were interpreted. Preferential solvation (specific solute-solvent interactions) or the solvent-solvent interaction is the reason for deviation from ideal behavior of probes.