Solvatochromism of Binary Mixtures of 2,2,2-Trifluoroethanol + Ionic Liquid [bmim][Tf ₂ N]: A Comparative Study with Molecular Solvents

The cosolvent modified ionic liquid (IL) systems have become an area of active research for the past few years because favorably modified properties can be achieved in such mixed systems which may enhance their utility as solvent media in chemical applications. Here, we show that mixtures of room temperature ionic liquid, 1-butyl-3-methylimidazoliumbis(trifluorosulphonyl)imide, [bmim][Tf ₂ N], and 2,2,2-trifluoroethanol (TFE) exhibit the fascinating circumstance of hyperpolarity. The normalized Reichardt polarity parameter ETN, hydrogen bond acidity (α), and basicity (β) of the TFE + IL mixtures are even higher than those of both neat TFE and IL components. A comparative study of TFE + IL has also been done with TFE + molecular organic solvents, polar protic (polyethylene glycol-200 and 1-butanol), polar aprotic (N,N-dimethylformamide), and nonpolar (1,4-dioxane) mixtures; however, these mixtures do not exhibit such a type of hyperpolarity behavior. The effect of solute-solvent as well as solvent-solvent interactions on the solvatochromic behavior of absorbance probes in TFE-based binary mixtures is considered a possible reason for the hyperpolarity. Further, a preferential solvation model approach and MD simulation study have been successfully used to gather information regarding the cybotactic region of indicator dyes and to achieve information on solvent-solvent and solute-solvent interactions in binary mixtures.