Electrogenerated chemiluminescence 69:: The tris(2,2′-bipyridine)ruthenium(II), (Ru(bpy)32+)/tri-n-propylamine (TPrA) system revisited -: A new route involving TPrA•+ cation radicals

The reaction occurring on electrooxidation of Ru(bpy)(3)(2+) (bpy = 2,2'-bipyridine) and tri-n-propylamine (TPrA) leads to the production of Ru(bpy)(3)(2+*) and light emission. The accepted mechanism of this widely used reaction involves the reaction of Ru(bpy)(3)(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)(2+*) was established, based on results of scanning electrochemical microscopy (SECM)-electrogenerated Chemiluminescence (ECL) experiments, as well as cyclic voltammetry simulations. A half-life of similar to0.2 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 similar to20 degreesC. The ESR spectra of the TPrA(.+) species consisted of a relatively intense and sharp septet with a splitting of similar to20 G and a g value of 2.0038.