OPTICAL ABSORPTION AND LUMINESCENCE OF C60F2X COMPOUNDS

We have investigated the reduction of initial C60 electronic structure under the influence of a growing number of attached fluorines in C60F48, C60F36, C60F24, and C60F18. The reduction of the low-energy π-electron subsystem reveals itself in lowering of the optical absorption in the visible region and in gradual blueshift of the luminescence. The absorption of C60F24 and C60F18 films strongly resembles that of C60, thus showing the similarity of electronic structures of C60 and these compounds. This resemblance disappears in the absorption spectra of C60F48 and C60F36. The absorption of these compounds looks like that of C6H6, because the π-bonds are isolated. The luminescence of C60F18 film has an unexpected two-component structure, with the first component close to the C60 luminescence spectra, and the second one lying pproximately in the same region with C60F36. We attribute this splitting of luminescence spectra to the two different channels for relaxation of the electronic excitation. The first one is correlated with the fluorinated part of the C60F18 molecule, the second one with the part free of fluorine atoms.