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 3[bmim]+* 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 3[bmim]+*. And the reaction that the hydrated electron captured by [bmim]+ to produce [bmim] in solution was observed.

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► The transient absorption spectra of neat [bmim][BF4] and its solution were recorded.
► Due to the different local structure, their transient absorption spectra were similar but not identical.
► 3[bmim]+*, [bmim]2+ and [bmim] were produced after laser photolysis of [bmim][BF4].
► Photoinduced processes such as energy transfer and electron capture by [bmim]+ were observed.