Generation by Electron Transfer of an Emitting State Not Observed by Photoexcitation in a Linked Ru(bpy)3-Methyl Viologen

The molecule in which a methyl viologen (MV2+) moiety is coupled through a three-carbon chain to one bipyridine in Ru(bpy)3 (bpy ) 2,2′bipyrine), [Ru(bpy)2(4-(2-(1′-methyl-4-4′-bipyridinediium-1-yl)propyl)-4′-methyl2,2′-bipyridine), abbreviated Ru(bpy)2(MV-bpy)], does not emit upon photoexcitation because of rapid quenching of the MLCT state by the MV2+. The integrated steady-state photoemission intensity is <1/1000 that of Ru(bpy)3 under the same conditions. However, quite efficient emission [∼1/5 that of Ru(bpy)3] is found when Ru(bpy)2(MV2+-bpy)5+ is electrogenerated at a Pt electrode in aqueous solution and reacts with a suitable coreactant (tri-npropylamine 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.