Observing the complete solvation response of DCS in imidazolium. ionic liquids, from the femtosecond to nanosecond regimes

Femtosecond Kerr-gated emission spectroscopy and picosecond time-correlated single photon counting are used to measured the full solvation response of 4-dimethylamino-4'-cyanostilbene in three imidazolium ionic liquids. The liquids studied are comprised of the 3-butyl-1-methylimidazolium cation '(Im(41)(+))' and the anions hexafluorophosphate, bis(trifluoromethylsulfonyl)imide ('Tf2N-'), and tris(trifluoromethylsulfonyl)methide ('Tf3C-'). In all three liquids the solvation response is widely distributed in time with important contributions extending from 100 fs to 10 ns. The amplitude of the fastest (< 1 ps) portion of the dynamics is correlated to the relative size and/or mass of the anion and it increases in the order Tf3C- < Tf2N- < PF6-. (c) 2005 Elsevier B.V. All rights reserved.