Different measures of polarity and nucleophilicity of a range of ionic liquids have been investigated using two solvatochromic dyes; the polarity appears to be largely cation controlled, while the donor strength is entirely anion dependent.

Ultrafast solvent dynamics of room-temperature ionic liquids have been investigated by optical heterodyne-detected Raman-induced Kerr-effect spectroscopy ~OHD-RIKES! by studying the effects of cation and anion substitution on the low frequency librational modes. The spectra of two series of imidazolium salts are presented. The first series is based on the 1-butyl-3-methylimidazolium salts @bmim#1 containing the anions trifluoromethanesulfate @TfO#2, bis~trifluoromethanesulfonyl!imide @Tf2N#2, and hexafluorophosphate @PF6#2. The second series is based on @Tf2N#2 salts containing the three cations 1-butyl-2,3-dimethylimidazolium @bmmim#1, 1-methyl-3-octylimidazolium @omim#1, and @bmim#1. It is found in all five samples that the signal is due to libration of the imidazolium ring at three frequencies around 30, 65, and 100 cm21 corresponding to three local configurations of the anion with respect to the cation

The novel application of ionic liquids as media for radiolytic generation and UV-vis-NIR spectroscopic characterization of radical ions is described. The redox properties of neat 1-butyl-3-methylimidazolium salts and their aqueous solutions have been investigated by means of pulse radiolysis. Furthermore, ionic liquids prove to be ideal media for the simultaneous generation of radical cations and anions. The radical cations generated from 1-methyl-1,4-dihydronicotinamide, a structural analogue of NADH, have been spectroscopically characterized under matrix conditions for the first time.

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