Explicit Solvent Modeling of Solvatochromic Probes in Ionic Liquids: Implications of Solvation Shell Structure

Calculations of absorption spectra have been performed for three solvatochromic dyes (para-nitroaniline, N,N-diethyl-para-nitroaniline, and Reichardt’s dye) in four ionic liquids based on 1-ethyl-3-methylimidazolium cation. Different variants of explicit solvent model have been used: fully explicit representation of solvent ions, charge embedding method, and mixed approach. Electrostatic solute–solvent interactions have been shown to induce structuring of the solvation shell around dipolar solute, causing significant and nonmonotonic dependence of calculated transition energies on the number of ion pairs included in calculations. A mixed approach with few fully explicit solvent ions embedded in electrostatic field of point charges appears as a promising method of calculations of solvatochromic response, provided that sufficiently large system sizes are used in explicit solvent modeling.