Effects of electron withdrawing and donating groups on the efficiency of tris(2,2\u27-bipyridyl)ruthenium(ii)/tri-n-propylamine electrochemiluminescence

The effects of electron withdrawing and electron donating groups on the electrochemiluminescent (ECL) properties of tris(2,2\u27-bipyridyl)ruthenium(II) (Ru(bpy)32+ where bpy = 2,2\u27-pyridine) are reported. The electrochemistry, photophysics and ECL of (bpy)2Ru(DC-bpy)2+, and (bpy)2Ru(DM-bpy)2+ (DC = 4,4\u27-dicarboxy-2,2\u27-bipyridine; DM = 4,4\u27-dimethyl-2,2\u27-bipyridine) have been studied relative to Ru(bpy)32+ in 50∶50 (v/v) acetonitrile(CH3CN)∶H2O (0.1 M KH2PO4), and aqueous solutions. Furthermore, the effects of Triton X-100 (polyethylene glycol tert-octylphenyl ether) on the electrochemical, spectroscopic and ECL properties of these compounds are reported. The anodic oxidation of Ru(bpy)32+, (bpy)2Ru(DC-bpy)2+, and (bpy)2Ru(DM-bpy )2+ produces ECL in the presence of tri-n-propylamine (TPrA) in all solvent systems. ECL efficiencies (ϕecl, photons produced per redox event) of 0.73 and 0.84 for (bpy)2Ru(DC-bpy)2+, and (bpy)2Ru(DM-bpy)2+ were obtained in aqueous buffered solution, using Ru(bpy)32+ as a relative standard (ϕecl = 1.0). Addition of 0.4 mM Triton X-100 results in a greater than 2-fold increase in ECL efficiences (i.e., 3.8, 2.4 and 2.3 for Ru(bpy)32+, (bpy)2Ru(DC-bpy)2+, and (bpy)2Ru(DM-bpy)2+, respectively) using aqueous Ru(bpy)32+ containing no surfactant as standard (ϕecl = 1.0). ECL efficiencies of 27.4, 16.5 and 26.1 were found in 50∶50 (v/v) CH3CN∶H2O (0.1 M KH2PO4) for Ru(bpy)32+, (bpy)2Ru(DC-bpy)2+, and (bpy)2Ru(DM-bpy)2+, respectively, using aqueous Ru(bpy)32+ containing no surfactant as standard (ϕecl = 1.0). Detailed studies support adsorption of surfactant on the electrode surface, thus facilitating TPrA and ruthenium oxidation