A comparative study of solvation dynamics in room-temperature ionic liquids.

The solvation dynamics of ionic liquids have been the subject of many experimental and theoretical studies but remain poorly understood. We analyze these dynamics by modeling the time-resolved fluorescence response of coumarin 153 in two room-temperature ionic liquids: 1-butyl-1-methylpyrrolidinium bromide and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide. Our results demonstrate that phenomena such as electrostatic screening operate significantly differently in the two liquids, and the relative importance of translational and rovibrational components of the ionic response depends significantly on the character of the ions involved. However, collective motion dominates the response of both ionic liquids, and the qualitative features of this collective behavior are strikingly similar in both cases.