Effects of electron withdrawing and donating groups on the efficiency of tris(2,2′-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'-bipyridyl)ruthenium(II) (Ru(bpY)(3)(2+) where bpy = 2,2'-pyridine) are reported. The electrochemistry, photophysics and ECL of (bpY)(2)Ru(DC-bpy)(2+), and (bpy)(2)Ru(DM-bpy)(2+) (DC = 4,4'-dicarboxy-2,2'-bipyridine; DM = 4,4'-dimethyl-2.2'-bipyridine) have been studied relative to Ru(bpy)(3)(2+) 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)(3)(2+), (bpy)(2)Ru(DC-bpy)(2+), and (bpy)(2)Ru(DM-bpy)(2+) produces ECL in the presence of tri-n-propylamine (TPrA) in all solvent systems. ECL efficiencies (01, photons produced per redox event) of 0.73 and 0.84 for (bpy)(2)Ru(DC-bpy)(2+), and (bpy)(2)Ru(DM-bpy)(2+) were obtained in aqueous buffered solution, using Ru(bpy)(3)(2+) as a relative standard (phi(ecl) = 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)(3)(2+), (bpy)(2)Ru(DC-bpy)(2+), and (bpY)(2)Ru(DM-bpy)(2+), respectively) using aqueous Ru(bPY)(3)(2+) containing no surfactant as standard (phi(ecl) = 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)(3)(2+), (bpY)(2)Ru(DC-bpy)(2+), and (bpy)(2)Ru(DM-bpy)(2+), respectively, using aqueous Ru(bpy)(3)(2+) containing no surfactant as standard (phi(ecl) = 1.0). Detailed studies support adsorption of surfactant on the electrode surface, thus facilitating TPrA and ruthenium oxidation.