A SPECTROELECTROCHEMICAL AND PHOTOCHEMICAL INVESTIGATION OF PHOTOINDUCED ELECTRON TRANSFER REACTION BETWEEN MG(II) PORPHYRIN AND VIOLOGEN

摘要

The spectroelectrochemical and photochemical characterization of MgTAP is presented; TAP=meso-tetra-p-(N-ethyl-N, N-dimethyl)anilinoporphyrin. It has been found that spectroscopic changes following one-electron oxidation of MgTAP, at E(1/2)=0.78+/-0.01 V versus NHE, and those succeeding photooxidation of the Mg(II) porphyrin by EtV are analogous; EtV= ethylviologen. As assigned by ESR spectroscopy, the electrochemical as well as the photochemical oxidation results in the production of the porphyrin pi cation-radical, [MgTAP](+), as a main product. In aqueous solution of EtV, the fluorescence of MgTAP* at lambda(em)=622 nm decreases obeying the Stern-Volmer equation (K-SV=47.7). This suggests that the reaction proceeds by the mechanism of oxidative quenching of MgTAP* fluorescence by EtV as an electron acceptor. The reaction system consisting of MgTAP/EtV/TEA, exposed to illumination at lambda(ex)=430 nm, results in the photogeneration of the viologen rr cation-radical, [EtV](+), with the quantum yield of Phi 5=0.82+/-0.1 mol/einstein; TEA=triethanolamine. Application of MgTAP as an electron-donating sensitizer of water photodecomposition into hydrogen and oxygen is considered. [References: 51]