Magnetic Field Effects on the Photoinduced Electron-Transfer Reactions in a Ruthenium Porphyrin-C60 Ligand Complex

Magnetic field effects (MFEs) on a photoinduced electron-transfer reaction in a semi-rigid linked system (RuP-C-60) were examined in toluene and o-dichlorobenzene. The transient absorption spectra indicated that the photogenerated biradical produced by an intramolecular electron-transfer reaction was observed only in o-dichlorobenzene. The decay rate constants (k (d)) for the biradical decreased steeply at lower magnetic fields (a parts per thousand currency sign0.06 T) and rapidly recovered at 0.08 T. The k (d) value was observed to decrease gradually above 0.2 T. The MFEs strongly indicated the formation of the singlet-born biradical for RuP-C-60. The dip in the MFE at 0.06 T was ascribed to the S-T level crossing mechanism. The MFEs above 0.2 T can be explained by a spin-spin relaxation mechanism due to the anisotropic Zeeman interaction being related to the exchange interaction.