Electrogenerated Chemiluminescence of the Tris(2,2′-bipyridine)ruthenium(II)/Tertiary Amine Systems: Effects of Electrode Surface Hydrophobicity on the Low-Oxidation-Potential Emission

Abstract

Previous studies revealed an electrogenerated chemiluminescence (ECL) of the [Ru(bpy)3]2+ (bpy = 2,2'-bipyridine)/tri-n-propylamine (TPrA) system at electrode potentials well before the oxidation of [Ru(bpy)3]2+. The low-oxidation-potential (LOP) ECL signals can be produced efficiently at bare glassy carbon and fluorosurfactant (i.e., Zonyl FSO or FSN) modified gold electrodes. Herein, we compare the LOP ECL behavior of [Ru(bpy)3]2+ with different tertiary amines as the coreactants. The amines studied include tri-n-ethylamine (TEtA), TPrA, and tri-n-butylamine (TBuA). At the FSO-modified gold electrode, the electro-oxidation of the amines becomes more facile as the FSO adsorption layer is more compact; however, the LOP ECL signals increase first and then decrease. The results suggest that the hydrophobicity of the electrode surface plays an important role in determining the ECL behavior. The drop of the emission intensity at the electrodes with a high coverage of FSO may result from the lifetime shortening of the amine cation radicals in a less polar reaction layer. An unexpected weak LOP ECL signal was found for the [Ru(bpy)3]2+/TBuA system, which is attributed to the extremely short lifetime of TBuA cation radicals at the hydrophobic electrode. This work provides more evidence of the effects of electrode surface hydrophobicity on the coreactant ECL systems.