Solvatochromic Parameters and Preferential Solvation Behavior for Binary Mixtures of 1,3-Dialkylimidazolium Ionic Liquids with Water

Abstract

Binary mixtures of 1,3-dialkylimidazolium based ionic liquids (ILs) and water were selected as solvent systems to investigate the solute-solvent and solvent-solvent interactions on the preferential solvation of solvatochromic indicators at 25 °C. Empirical solvatochromic parameters, dipolarity/polarizability (π*), hydrogen-bond donor acidity (α), hydrogen-bond acceptor basicity (β), and Reichardt's polarity parameters (ENT) were measured from the ultraviolet-visible spectral shifts of 4-nitroaniline, 4-nitroanisole, and Reichardt's dye. The solvent properties of the IL-water mixtures were found to be influenced by IL type and IL mole fraction (xIL). All these studied systems showed the non-ideal behavior. The maximum deviation to ideality for the solvatochromic parameters can be obtained in the xIL range from 0.1 to 0.3. For most of the binary mixtures, the π* values showed the synergistic effects instead of the ENT, α and β values. The observed synergy extent was dependent on the studied systems, such as the dye indicator and IL type. A preferential solvation model was utilized to gather information on the molecular interactions in the mixtures. The dye indicator was preferentially solvated on the following trend: IL>IL-water complex>water.