Photoinduced electron transfer between metal octaethylporphyrins and fullerenes (C60/C70) studied by laser ash photolysis: electron-mediating and hole-shifting cycles

Electron transfer (ET) processes of fullerenes (C-60/C-70) with metal octaethylporphyrins ( MOEP) in a polar solvent have been investigated by a nanosecond laser photolysis technique in the visible/near-IR regions. By the selective excitation of C-60/C-70 using OPO laser light it has been proved that electron transfer takes place from the ground states MOEP to the triplet excited states C-3(60)*/C-3(70)*. By selective excitation of MOEP the electron transfer processes via (MOEP)-M-3* to C-60/C-70 were also confirmed. In nonpolar toluene the lifetimes of C-3(60)*/C-3(70)* decreased in the presence of MOEP without evidence for electron and/or energy transfer processes. On adding benzonitrile to toluene the ion-radical formation was increased, suggesting that the triplet exciplexes (3)[MOEP(delta+)-C-60((delta-))/C-70((delta-))]* would be dominant prior to the ion-pair formation in a less-polar solvent. On addition of a viologen dication the electron of the anion radicals of C-60/C-70 transfers to the viologen dication yielding the viologen radical cation. In the system MOEP C-60/C-70-aromatic amine (DTQH), as a second donor having lower oxidation potential than MOEP, the hole shift from the radical cation of MOEP to the aromatic amine was observed. These observations proved that the photosensitized electron-transfer/electron-mediating and photosensitized electron-transfer/hole-shift cycles have been confirmed by the transient absorption spectral method.