The Effects of Nonionic Surfactants on the Tris(2,2\u27-bipyridyl)ruthenium(II)-Tripropylamine Electrochemiluminescence System

The electrochemistry and electrogenerated chemiluminescence (ECL) of Ru(bpy)32+ (bpy = 2,2‘-bipyridyl) were studied in the presence of the nonionic surfactants Triton X-100, Thesit, and Nonidet P40. The anodic oxidation of Ru(bpy)32+ produces ECL in the presence of tri-n-propylamine in both aqueous and surfactant solutions. Increases in both ECL efficiency (≥8-fold) and duration of the ECL signal were observed in surfactant media. A shift to lower energies of the Ru(bpy)32+ ECL emission by ∼8 nm was also observed. The one-electron oxidation of Ru(bpy)32+ to Ru(bpy)33+ occurs at +1.03 V vs Ag/AgCl in aqueous buffered (0.2 M potassium phosphate) solution as found by square wave voltammetry. This potential did not shift in surfactant systems, indicating that the red-shifts in ECL emission are due to stabilization of ligand π* orbitals in the metal-to-ligand charge-transfer excited state. These results are consistent with hydrophobic interactions between Ru(bpy)32+ and the nonionic surfactants