Electronic structures of ionic liquids [Cnmim]+BF4- and [Cnmim]+PF6- studied by ultraviolet photoemission, inverse photoemission, and near-edge X-ray absorption fine structure spectroscopies

Electronic structures of the ionic liquids formed by 1-butyl-3-alkylimidazolium ion [Cnmim]+ (n = 4, 8, 10) with fluorine-containing anions (tetrafluoroboronate BF4-, hexafluorophosphate PF6-) were studied by ultraviolet photoemission spectroscopy (UPS) and inverse photoemission spectroscopy (IPES). It was found that the energy gaps of these ionic liquids are determined by cations only.