Medium effects on the spectroscopy and intramolecular energy redistribution of C60 in cryogenic matrices

We review some of our works on the absorption, excitation and emission spectra of C60 embedded in rare gas matrices while stressing the role of the environment. The gas phase resonant two-photon ionization spectrum of C60 is reanalysed in the light of our previous work and the energy of the lowest three excited singlet states is determined with precision. In matrices, the visible absorption bands are red-shifted by an amount ranging from ∼30 cm−1 in Ne matrices to ∼330 cm−1 in Xe matrices. The observed reversal of state ordering of the lowest two singlets states (T1g and T2g) between Ne and Ar matrices (in emission) and in Ne matrices, between the absorption and emission spectra, is attributed to different Stokes shifts of the T1g and T2g states and to the small energy splitting (∼50 cm−1) between them. Finally, a detailed picture of the intramolecular energy redistribution processes is obtained thanks to a combination of picosecond fluorescence experiments and femtosecond pump–probe transient absorption experiments. The intramolecular relaxation processes among the pure electronic levels of the lowest three singlet states are found to be strongly medium dependent. Medium effects are manifest even on the very short time scale of the internal conversion in the singlet vibronic manifold.