PHOTOINDUCED ELECTRON-TRANSFER REACTION BETWEEN [CU(DMP)P-2](+OR-) (P=PPH(3) OR PPH(2)(M-C6H4SO3-) AND VIOLOGEN DERIVATIVES

The copper(I) complex, [Cu(dmp)P-2](+or-) (dmp = 2,9-dimethyl-1,10-phenanthroline, P = triphenylphosphine PPh(3) or diphenylphosphinobenzene-m-sulfonate PPh(2)(m-C6H4SO3-)), catalytically photoreduces viologen derivatives, dicationic methyl viologen MV(2+) and neutral propylviologen disulfonate PVS0. The quantum yield phi(V-.) for the viologen photoreduction is discussed on the basis of the lifetime of the photosensitiser, formation of the encounter complex, dissociation of the encounter complex to products, and back electron transfer in the encounter complex. When [Cu(dmp){PPh(2)(m-C6H4SO3)}(2)](-) is used for the photoreduction of MV(2+), the highest quantum yield (phi(V-.)(Tr)=0.03) is obtained. Kinetic analysis and measurements of the excited state lifetime reveal that this best phi(V-.) value arises from the rapid formation of the encounter complex, owing to the attractive electrostatic interaction between anionic [Cu(dmp){PPh(2)(m-C6H4SO3)}(2)](-) and cationic MV(2+).