Self-quenching in the electrochemiluminescence of Ru(bpy)32+ using ascorbic acid as co-reactant

In this study, electrochemiluminescence (ECL) of Ru(bpy)(3)(2+) (bpy = 2,2'-bipyridyl) using ascorbic acid (H(2)A) as co-reactant was investigated in an aqueous solution. When H(2)A was co-existent in a Ru(bpy)(3)(2+)-containing buffer solution, ECL peaks were observed at a potential corresponding to the oxidation of Ru(bpy)(3)(2+), and the intensity was proportional to H(2)A concentration at lower concentration levels. The formation of the excited state *Ru(bpy)(3)(2+) was confirmed to result from the co-reaction between Ru(bpy)(3)(2+) and the intermediate of ascorbate anion radical (A(-)center dot), which showed the maximum ECL at pH = 8.8. It is our first finding that the ECL intensity would be quenched significantly when the concentration of H(2)A was relatively higher, or upon ultrasonic irradiation. In most instances, quenching is observed with four-fold excess of H(2)A over Ru(bpy)(3)(2+). The diffusional self-quenching scheme as well as the possible reaction pathways involved in the Ru(bpy)(3)(2+)-H(2)A ECL system are discussed in this study. Copyright (C) 2008 John Wiley & Sons, Ltd.