Room-temperature ionic liquids were used as electrolytes for in situ studies of the transitions of solution cast fullerene films. 1-Butyl-3-methyl-imidazolium tetrafluoroborate (BMIMBF4), 1-butyl-3-methyl-imidazolium hexafluorophosphate (BMIMPF6) and 1-butyl-2,3dimethylimidazolium tetrafluoroborate (BDiMIMBF(4)) were used in this study and the techniques used are cyclic voltammetry and in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. Infrared spectra were recorded during the reversible redox processes of the C-60 films showing a three-step one electron reduction and reoxidation reaction. After reoxidation some part of the C-60 film remained in its C-60 form. The IR bands obtained during electrochemical reduction of C-60 in ionic liquids were compared with the spectra reported for C-60 films upon reduction in the presence of different cations in organic solutions. (c) 2006 Elsevier B.V. All rights reserved.