Journal of Physical Chemistry B, Vol.107, No.35, 9312-9318, 2003
Inter- and intramolecular photoinduced electron-transfer processes between C-60 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.