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

In this study, electrochemiluminescence (ECL) of Ru(bpy)₃²⁺ (bpy = 2,2′‐bipyridyl) using ascorbic acid (H₂A) as co‐reactant was investigated in an aqueous solution. When H₂A was co‐existent in a Ru(bpy)₃²⁺‐containing buffer solution, ECL peaks were observed at a potential corresponding to the oxidation of Ru(bpy)₃²⁺, and the intensity was proportional to H₂A concentration at lower concentration levels. The formation of the excited state *Ru(bpy)₃²⁺ was confirmed to result from the co‐reaction between Ru(bpy)₃³⁺and the intermediate of ascorbate anion radical (A⁻•), 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 H₂A was relatively higher, or upon ultrasonic irradiation. In most instances, quenching is observed with four‐fold excess of H₂A over Ru(bpy)₃²⁺. The diffusional self‐quenching scheme as well as the possible reaction pathways involved in the Ru(bpy)₃²⁺–H₂A ECL system are discussed in this study. Copyright © 2008 John Wiley & Sons, Ltd.