The temperature dependence of Stokes shifts for solutes and their solvation dynamics in ionic liquids (ILs) is studied in the temperature range between 300 K and 500 K using molecular dynamics computer simulations. Two different types of solutes are considered: a simple rigid diatomic solute model and realistic coumarin 153. For ionic liquids, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI+Tf2N�), 1-ethyl-3-methylimidazolium hexafluorophosphate (EMI+PF6�), and 1-butyl-3-methylimidazolium hexafluorophosphate (BMI+PF6�) are studied. In all three ILs, the Stokes shifts of the two solutes show similar behaviors with temperature; the Stokes shift for the solute tends to decrease with increasing temperature. For coumarin 153, the Franck-Condon energy for steady-state emission decreases as temperature increases, while the Franck-Condon energy for absorption increases. In general, for both solutes, the solvent frequency that quantifies ultrafast sub-picosecond solvation dynamics shows little temperature dependence. By contrast, the longer dissipative relaxation component becomes significantly faster with rising temperature.

Temperature dependence of solvation in ionic liquids

248th National Meeting (2014)

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