OPTICAL ABSORPTION AND LUMINESCENCE OF C 60 F 2X COMPOUNDS

We have investigated the reduction of initial C 60 electronic structure under the influence of a growing number of attached fluorines in C 60 F 48, C 60 F 36, C 60 F 24, and C 60 F 18. 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 C 60 F 24 and C 60 F 18 films strongly resembles that of C 60, thus showing the similarity of electronic structures of C 60 and these compounds. This resemblance disappears in the absorption spectra of C 60 F 48 and C 60 F 36. The absorption of these compounds looks like that of C 6 H 6, because the π-bonds are isolated. The luminescence of C 60 F 18 film has an unexpected two-component structure, with the first component close to the C 60 luminescence spectra, and the second one lying pproximately in the same region with C 60 F 36. 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 C 60 F 18 molecule, the second one with the part free of fluorine atoms.