Optical transition and ionicity of C60/amine charge-transfer complexes studied by optical spectroscopy

We have investigated absorption spectra of charge-transfer (CT) complexes of C60 with various aromatic amines with different ionization potentials. An absorption band due to CT transition is observed in the visible region; with increasing ionization potential of amines, the peak energy shifts to the higher energy side and the oscillator strength of CT transition increases. We extract degrees of charge transfer by analyzing the transition energy of the CT band as a function of ionization potential and Raman spectra. The experimental results show that the CT complexes studied here have a neutral character in their ground state.