Fig. 2. Mechanisms involved in the co-reactant ECL of a mixture of [Ru(bpy)3]2+ (Ru2+) and [Ir(sppy)3]3− (Ir3−) with TPrA co-reactant, in circumstances in which TPrA and [Ir(sppy)3]3− (but not [Ru(bpy)3]2+) are oxidised. This occurs at potentials between 0.81 V and 1.06 V vs. SCE, and at higher potentials if the [Ru(bpy)3]2+ luminophore is not close enough to the electrode for its direct oxidation (e.g., when immobilised in bead-based assays). (a) The unenhanced ‘remote’ co-reactant ECL of [Ru(bpy)3]2+. An analogous pathway is not feasible for [Ir(sppy)3]3− because TPrA˙ cannot reduce that complex. (b) The ‘direct’ co-reactant ECL of [Ir(sppy)3]3−. As the [Ru(bpy)3]2+ is not oxidised under these conditions, it cannot generate light via this pathway. (c) The enhanced ECL of [Ru(bpy)3]2+. The reaction of [Ir(sppy)3]2− and [Ru(bpy)3]+ can generate [Ru(bpy)3]2+* and [Ir(sppy)3]3− (but not [Ru(bpy)3]2+ and [Ir(sppy)3]3−*).
