A comparative study on the ionic liquid [bmim][BF4] and its solution with transient absorption spectroscopy

A detailed study was explored to compare the transient absorption spectra of the neat 1-butyl-3-methylimidazolium tetrafluoroborate (bmim]BF₄]) with its solution in water or acetonitrile. It was concluded that the excited triplet state ³bmim]^+* was produced after 266 nm laser irradiation, and then the neutral radical bmim] and the cation radical bmim] ²⁺ were formed through two possible paths. The transient absorption spectra of the neat bmim]BF₄] and its solution were similar but the reaction kinetics were different due to their different local structures such as dimeric or cluster. The energy transfer between excited bmim]BF₄] and β-carotene further affirmed the existence of ³bmim]^+*. And the reaction that the hydrated electron captured by bmim]⁺ to produce bmim] in solution was observed.