Fluoride ion yield and absorption spectral analysis of irradiated imidazolium-based room-temperature ionic liquids

The radiation chemical yields of F ions (G(F−) values) were measured for a group of imidazolium-based room-temperature ionic liquids following 60Co gamma ray irradiation. The G(F−) values of ionic liquids: hexafluorophosphate, bis[(trifluoromethyl)sulfonyl]imide, trifluoromethanesulfonate and tetrafluoroborate anions associated with 1-butyl-3-methylimidazolium cations were determined to be 0.227, 0.136, 0.101 and 0.008 μmol J−1, respectively. The G(F−) value is dependent on the F-X (X=B, P, etc.) bond energy and the anion structure and can be considered as an indicator of the radiation stability of fluorine-containing ionic liquids. In addition, as confirmed by UV-Vis absorption measurement, the radiolytic products with strong photoabsorption and color darkening depend on the structures of both the cation and the anion.