Polarization effects on the solvation dynamics of coumarin C153 in ionic liquids: components and their...

The solvation dynamics of coumarin C153 dissolved in three selected molecular ionic liquids - EMIM(+)BF4(-), EMIM(+)TfO(-), and BMIM(+)BF4(-) - was studied by molecular dynamics simulations including polarization forces. The solvation response function was decomposed with respect to permanent and induced charge distributions, cationic and anionic contributions, and translational and non-translational motions. The latter decomposition was accomplished by an appropriate multipole expansion. Furthermore, the difference in solvation energy was resolved radially. The dynamics in the sub-picosecond regime was elucidated as the mutual translational motion of the solute and the cage formed by the first solvation shell. For a qualitative interpretation, solvent molecules can be reduced to "quasi-atomic" ions carrying a net charge at their molecular center of mass. Towards a quantitative description, the dipole moment serves as a measure of charge anisotropy.