Generation by electron transfer of an emitting state not observed by photoexcitation in a linked Ru(bpy)(3)(2+)-methyl viologen

The molecule in which a methyl viologen (MV(2+)) moiety is coupled through a three-carbon chain to one bipyridine in Ru(bpy)(3)(2+) (bpy = 2,2'bipyrine), [Ru(bpy)(2)(4-(2-(1'-methyl-4-4'-bipyridin-1-yl)propyl)-4' -methyl-2,2'-bipyridine), abbreviated Ru-II(bpy)2(MV(2+)-bpy)(4+)], does not emit upon photoexcitation because of rapid quenching of the MLCT state by the MV(2+). The integrated steady-state photoemission intensity is < 1/1000 that of Ru(bpy)(3)(2+) under the same conditions. However, quite efficient emission [similar to 1/5 that of Ru(bpy)(3)(2+)] is found when Ru-III(bpy)2(MV(2+)-bpy)(5+) is electrogenerated at a Pt electrode in aqueous solution and reacts with a suitable coreactant (tri-n-propylamine or oxalate), where the excited state is produced by an electron-transfer reaction. Electrogenerated chemiluminescence is also observed for this species in acetonitrile solutions upon potential cycling via annihilation of the reduced (+1) and oxidized (+5) species.