Efficient production of methyl viologen cation radicals using RuII systems

A number of RuII-diimine complexes were used to photosensitize methyl viologen cation radical (MV+) production in the presence of ethylenediaminetetraacetic acid (EDTA). An unusually high quantum yield (π(MV+) = 1.88) was obtained for [Ru(bpz)2dpq]2+ (bpz = 2′,2-bipyrazine; dpq = 2,3-di-(2′-pyridyl)-quinoxaline) at pH 11. This value is higher than any previously known for RuII complexes. The quantum yield is discussed in terms of the electron transfer quenching process and the cage escape effects which affect geminate recombination of the redox species. Time-resolved transient absorption spectra were used to study the formation of MV+ and RuI in the case of [Ru(bpz)2(dpq)]2+.