Molecular Dynamics Study of Polarity in Room-Temperature Ionic Liquids

Abstract

In this work, we use molecular dynamics simulation to explore the physical principles governing the polarity of room-temperature ionic liquids. We use the calculated absorption spectrum of the solvatochromic dye molecule betaine-30 as a proxy for polarity and characterize the solute−solvent interactions responsible for the solvatochromic shift. We analyze specific solute−solvent interactions and discuss the complications posed by the proximity of counterions in solution. We also explore the question of competition between solute−solvent and solvent−solvent interactions and find evidence supporting a recently proposed scheme for control of solvent polarity. Finally, we show that nonspecific electrostatic solute−solvent interactions are screened by the ionic solvent, dictating that the thermodynamic properties of solvation are determined by local interactions. However, thermal fluctuations create transient long-ranged solute−solvent interactions that could be important for chemical kinetics.

Dynamic Solvation in Imidazolium-Based Ionic Liquids on Short Time Scales

“…Given the small size of the model solute and the large changes in net charge, the motions of the resulting concentrated anionic charges may dominate the relaxation. In the experimental solvation dynamics studies of organic dye molecules such as coumarin 153 (C153) in RTILs, the charge distribution change is smeared across the whole probe 58 They obtained radial distribution functions indicating the proximity of the 1-butyl-3-methylimidazolium ring to the dye, which is consistent with our experimental observations for coumarin 153. The solvation relaxation is argued to arise from the translation and diffusional motion of ions.…”

Hydrogen-bond acidity of ionic liquids: an extended scale

“…20,41,42,53,54 Driven by the prediction results presented in Fig. 2, eqn (10) was then tested in order to assess its predictive ability towards new ILs or ILs with no experimental data yet available.…”

Assessing the Roles of the Constituents of Ionic Liquids in Dynamic Solvation: Comparison of an Ionic Liquid in Micellar and Bulk Form

“…[1][2][3][4] The importance of ionic liquids has consequently stimulated considerable interest in their dynamic solvation properties, both in the experimental and the theoretical arenas. [26][27][28][29][30][31][32] An intriguing aspect of certain ionic liquids, which has only recently become appreciated, is their ability to promote micelle formation or to form micelles themselves. [33][34][35][36] Major questions regarding dynamic solvation by ionic liquids deal with whether the organic cation or the inorganic anion solvate preferentially on different time scales, the role of the correlated motion of the ion pairs and their lifetime, and the importance of translational motion of the ions relative to dipolar relaxation.…”