Solvation dynamics of coumarin 153 in several classes of ionic liquids: cation dependence of the ultrafast component

Time-resolved emission spectroscopy with 25 ps resolution is used to measure the dynamics of solvation of coumarin 153 in four ionic liquids (ILs), comprising three (imidazolium, ammonium, and phosphonium) cation classes. All four liquids possess similar electronic and nuclear polarizabilities. Solvation in the imidazolium ILs is biphasic, consisting of ultrafast (<5 ps) and slow (ns) components of roughly equal amplitudes near room temperature, whereas the ammonium and phosphonium ILs lack the ultrafast portion of the response. The slow solvation component displays kinetics typical of glass-forming liquids and tracks solution viscosity in a similar manner in all of the ILs.