This article shows our recent study on electronic structure of several typical ionic liquids. Ultraviolet photoemission spectroscopy, inverse photoemission spectroscopy and soft x-ray emission spectroscopy (SXES) were used for elucidating the electronic structure of ionic liquids based on methylbutylimidazolium ([C
n mim]
+) cation. Non-resonant SXES spectra measured above N, O, and F 1s edges selectively probed the partial density of states of the cation and anion. They give a clear evidence that the highest occupied molecular orbital of the [C
4 mim]
+ cation contributes to the topmost occupied states of the ionic liquids [C
4 mim]
+PF
6−. Resonant soft x-ray emission spectra at the N 1s edge of these ionic liquids revealed that the energy gap of [C
4 mim]
+PF
6− is solely determined by the [C
4 mim]
+ cation, in contrast to usual ionic crystals like NaCl and NaBr. The ionic liquids composed of fluoride anions PF
6− and BF
4− have anomalous electronic structure. Such basic knowledge about the electronic structure of ionic liquid must be helpful for new molecular design of ionic liquids.
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