Inter- and Intramolecular Photoinduced Electron-Transfer Processes between C60 and Diphenylaminofluorene in Solutions

Intramolecular photoinduced charge-separation and charge-recombination processes of a covalently bonded buckminsterfullerene−diphenylaminofluorene (C 60 −DPAF) dyad, in which the diphenylaminofluorene moiety is connected to C 60 via a ketone group, have been investigated. Quenching of the fluorescence intensities and the observed short fluorescence lifetimes of the C 60 moiety of the dyad in benzonitrile (PhCN) and DMF indicated that charge separation takes place via the singlet excited state of the C 60 moiety at a fast rate with high efficiency. On the basis of the nanosecond transient absorption spectra, formation of the radical ion pair C 60 •- -DPAF •+ was confirmed in DMF; the radical ion pair decays with a lifetime of 150 ns. From the temperature dependence of the charge-recombination rate constants, the reorganization energy was evaluated to be 0.81 eV in DMF, which is reasonably small, characteristic of fullerene derivatives. On the other hand, a mixture of DPAF and C 60 showed intermolecular electron transfer via the triplet state of C 60 in polar solvents such as PhCN.