Two-Electron Reduction of [{(bpy)2Ru(dmbbbpy)}3Ru]8+ from (BNA)2 via Photoinduced Electron Transfer [dmbbbpy = 2,2‘-Bis(N-methylbenzimidazole-2-yl)-4,4‘-bipyridine]

Photoirradiation (λ > 500 nm) of [{(bpy)2Ru(dmbbbpy)}3Ru]8+ (18+) (dmbbbpy = 2,2‘-bis(N-methylbenzimidazole-2-yl)-4,4‘-bipyridine and bpy = 2,2‘-bipyridine) in the presence of dimeric N-benzyldihydronicotinamide, (BNA)2, produced stable two-electron reduced species (16+). Laser flash photolysis and emission spectroscopy were used to understand the reductive reaction pathways. The emission quenching kq value (4.1 × 109 M-1 s-1) obtained from Stern−Volmer plot is in excellent agreement with the electron-transfer rate constant, ket (4.7 × 109 M-1 s-1) determined from the decay kinetics of transient 318+ triplet−triplet absorption at 650 nm indicating that photoreduction of 18+ proceeds via photoinduced electron transfer from (BNA)2 to 318+*. After bimolecular electron-transfer process, 18+ was reduced to 17+ and the electron donor (BNA)2 was oxidized. Oxidation of (BNA)2 leads to the formation of highly reactive species, BNA• which then reduces 17+ to 16+. The quantum yield for the formation of the photoredu...