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

Abstract

Intramolecular photoinduced charge-separation and charge-recombination processes of a covalently bonded buckminsterfullerene−diphenylaminofluorene (C60−DPAF) dyad, in which the diphenylaminofluorene moiety is connected to C60 via a ketone group, have been investigated. Quenching of the fluorescence intensities and the observed short fluorescence lifetimes of the C60 moiety of the dyad in benzonitrile (PhCN) and DMF indicated that charge separation takes place via the singlet excited state of the C60 moiety at a fast rate with high efficiency. On the basis of the nanosecond transient absorption spectra, formation of the radical ion pair C60•--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 C60 showed intermolecular electron transfer via the triplet state of C60 in polar solvents such as PhCN.