Electrogenerated Chemiluminescence. 67. Dependence of Light Emission of the Tris(2,2‘)bipyridylruthenium(II)/Tripropylamine System on Electrode Surface Hydrophobicity

We describe the effect of electrode surface hydrophobicity on the electrochemical behavior and electrogenerated chemiluminescence (ECL) of Ru(bpy)3(2+) (bpy = 2,2'-bipyridyl)/tripropylamine (TPrA) system. Gold and platinum electrodes were modified with different thiol monolayers. The hydrophobicity of the electrode surfaces changed with different terminal groups of the thiol molecules. The oxidation rate of TPrA was found to be much larger at the modified electrode with a more hydrophobic surface. The adsorption of neutral TPrA species on this kind of surface was assumed to contribute to the faster anodic kinetics. Due to the rapid generation of the highly reducing radical, TPrA., ECL intensity increased significantly at more hydrophobic electrodes. This electrode surface effect in the ECL analytical system allows one to improve the detection sensitivity at low concentrations of Ru(bpy)3(2+). The surfactant effect on the ECL process was also examined and discussed based on the change of electrode hydrophobicity by the adsorption of surfactant species.