Electrochemiluminescence of the [Ru(bpy)3]2+ Complex: The Coreactant Effect of PAMAM Dendrimers in an Aqueous Medium

Electrogenerated chemiluminescence (ECL) from aqueous solutions of tris(2,2'-bipyridine)ruthenium(II), [Ru(bpy)(3)](2+), in the presence of PAMAM G1.5 and G4.5 dendrimers, was observed without the addition of coreactants. The ECL efficiency, Phi(ECL), was enhanced with the addition of increasing amounts of G1.5 dendrimer. Indeed, the ECL efficiency for the [Ru(bpy)(3)](2+)/G1.5 dendrimer became about 10 times higher than that for the [Ru(bpy)(3)](2+)/oxalate anion system. However, the ECL efficiency in the presence of the G4.5 dendrimer was smaller than that for the G1.5 dendrimer at concentrations similar to those for G1.5 with identical medium conditions. Besides, the addition of NaCl at a given concentration of G1.5 dendrimer decreased the ECL efficiency. The results of (Phi(ECL) were interpreted by taking into account the coreactant effect and the electrostatic (long-range and short-range) interactions between the ruthenium(II) complex and the electric field of the dendrimer surface. Standard formal potentials of the [Ru(bpy)(3)](3+/2+) couple in the presence of G1.5 and G4.5 dendrimers were also determined.