Electrochemiluminescent Reaction between Ru(bpy)3 2+ and Oxygen in Nafion Film

For years, dissolved oxygen (O2) has been regarded as a quenching species in Ru(bpy)3 2+ electrochemiluminescent (ECL) systems; however, in the present study, O2 was found to act as a coreactant for Ru(bpy)3 2+ ECL in Nafion film, resulting in a strong ECL light emission. ECL experiments were carried out at a Ru(bpy)3 2+/Nafion film-modified glassy carbon electrode (GCE) immersing in air-saturated phosphate buffer solution (pH 7.4). Scanning in the potential range of +1.5 to −1.0 V resulted in three luminescent processes, including two potential-dependent luminescence peaks (ECL-1 and ECL-2), and one potential-independent persistent luminescence emission (CL-P). Therein, ECL-2 occurring at potential less than −0.5 V was demonstrated to be a new chemiluminescent reactions between O2 and Ru(bpy)3 2+. In ECL-2, Nafion film plays important roles in stabilizing Ru(bpy)3 3+ and O2 •− radical essentially for producing the new ECL. Unlike previously reported ECL processes, ECL-2 peak potential is dependent on the reduction potential of the coreactant (i.e., O2) rather than the redox potentials of the luminopore, Ru(bpy)3 2+, which would provide a useful way to probe O2, O2 •− radical, and their stabilities in electrochemical reactions.