Photoinduced electron-transfer and electron-mediation processes from the excited triplet state of zinc tetraphenylporphyrin ((ZnTPP)-Zn-3*) to the hexyl viologen dication (HV2+) in the presence of oxo-acetato-bridged triruthenium clusters, [Ru-3(mu(3)-O)(mu-CH3CO2)(6)L-3](+), have been revealed by the transient absorption spectra in the visible and near-IR regions. By the nanosecond laser-flash photolysis of ZnTPP in the presence of HV2+ and [R mu(3)(mu(3)-O)(mu-CH3CO2)(6)L-3](+), the transient absorption bands of the radical cation of ZnTPP (ZnTPPcenter dot+) and the reduced viologen (HVcenter dot+) were initially observed with the concomitant decay of 3ZnTPP*, after which an extra electron of HVcenter dot+ mediates to [Ru-3(mu(3)-O)(mu-CH3CO2)(6)L-3](+), efficiently generating [Ru-3(mu(3)-O)(mu-CH3CO2)(6)L-3](0) with high potential. Although back-electron transfer took place between ZnTPPcenter dot+ and [Ru-3(mu(3)-O)(mu-CH3CO2)(6)L-3](0) in the diffusion-controlled limit, [Ru-3(mu(3)-O)(mu-CH3CO2)(6)L-3](0) accumulates at a steady concentration upon further addition of 1-benzyl-1,4dihydronicotinamide (BNAH) as a sacrificial donor to re-produce ZnTPP from ZnTPPcenter dot+. Therefore, vie established a novel system to accumulate [Ru-3(mu(3)-O)(mu-CH3CO2)(6)L-3](0) as an electron pool by the excitation of ZnTPP as photosensitizing electron donor in the presence of HV2+ and BNAH as an electron-mediating reagent and sacrificial donor, respectively. With the increase in the electron-withdrawing abilities of the ligands, the final yields of [Ru-3(mu 3-O)(mu-CH3CO2)(6)L-3](0) increased.