Magnetic field effects on photoelectrochemical reactions of modified electrodes with C₆₀-phenothiazine nanoclusters

Magnetic field effects on the photoelectrochemical reactions of photosensitive electrodes modified with C₆₀ nanoclusters were examined, intended for the development of nanodevices where photofunctions were controllable with magnetic field. Mixed clusters of a C₆₀ derivative (C₆₀N⁺) containing a positive charge and methylphenothiazine (MePH) were prepared by dissolving them in the THF-H₂O mixed solvent. Diameters of the clusters were estimated to be ca. 100 nm from dynamic light scattering and AFM measurements. Photofunctional electrodes with the nanoclusters of C₆₀N⁺ and MePH were fabricated on the electrodes modified with a self-assembled monolayer of HS(CH₂)₂SO₃^-Na⁺ on a gold substrate. The photocurrent action spectrum of the cluster-modified electrode strongly indicates that the photocurrents are ascribed to the photoexcitation of the nanoclusters of C₆₀N⁺. Furthermore, the photocurrents increased with increasing an external magnetic field, typically 3% at 0.5 T. The profile of magnetic field dependence on the photocurrents is in good agreement with the results on the dynamics of radical pair in the nanoclusters of C₆₀N⁺ and MePH in the THF-H₂O mixed solvent. This is suggested that the magnetic field effects are ascribable to the contribution of triplet radical pair that are generated by photoinduced intermolecular electron-transfer from MePH to triplet excited state of nanocluster of C₆₀N⁺, and are explained in terms of spin-lattice relaxation mechanism in radical pair mechanism.