Two-electron reduction of [{(bpy)(2)Ru(dmbbbpy)}(3)RU](8+) from (BNA)(2) via photoinduced electron transfer [dmbbbpy = 2,2 '-bis(N-methylbenzimidazole-2-yl)-4,4 '-bipyridine]

Photoirradiation (lambda > 500 nm) of [{(bpy)(2)Ru(dmbbbpy)}(3)Ru](8+) (1(8 +)) (dmbbbpy = 2,2'-bis(N-methylbenzimidazole-2-yl) -4,4'-bipyridine and bp y = 2,2'-bipyridine) in the presence of dimeric N-benzyldihydronicotinamide , (BNA)(2), produced stable two-electron reduced species (1(6+)). Laser fla sh photolysis and emission spectroscopy were used to understand the reducti ve reaction pathways. The emission quenching k(q) value (4.1 x 10(9) M-1 s( -1)) obtained from Stern-Volmer plot is in excellent agreement with the ele ctron-transfer rate constant, k(et) (4.7 x 10(9) M-1 s(-1)) determined from the decay kinetics of transient (3)1(8+) triplet-triplet absorption at 650 nm indicating that photoreduction of 1(8+) proceeds via photoinduced elect ron transfer from (BNA)(2) to (3)1(8+*). After bimolecular electron-transfe r process, 1(8+) was reduced to 1(7+) and the electron donor (BNA)(2) was o xidized. Oxidation of (BNA)(2) leads to the formation of highly reactive sp ecies, BNA(.) which then reduces 1(7+) to 1(6+). The quantum yield for the formation of the photoreduction product was 0.026.