Electrogenerated Chemiluminescence 69 : The Tris ( 2 , 2 ′-bipyridine ) ruthenium ( II ) , ( Ru ( bpy ) 32 + ) / Trin-propylamine ( TPrA ) System Revisited s A New Route Involving TPrA

The reaction occurring on electrooxidation of Ru(bpy)3 (bpy ) 2,2′-bipyridine) and tri-npropylamine (TPrA) leads to the production of Ru(bpy)3 and light emission. The accepted mechanism of this widely used reaction involves the reaction of Ru(bpy)3 and a reduced species derived from the free radical of the TPrA. However, this mechanism does not account for many of the observed features of this reaction. A new route involving the intermediacy of TPrA cation radicals (TPrA•+) in the generation of Ru(bpy)3 was established, based on results of scanning electrochemical microscopy (SECM)-electrogenerated chemiluminescence (ECL) experiments, as well as cyclic voltammetry simulations. A half-life of ∼0.2 ms was estimated for TPrA•+ in neutral aqueous solution. Direct evidence for TPrA•+ in this medium was obtained via flow cell electron spin resonance (ESR) experiments at ∼20 °C. The ESR spectra of the TPrA•+ species consisted of a relatively intense and sharp septet with a splitting of ∼20 G and a g value