Electrogenerated Chemiluminescence. 62. Enhanced ECL in Bimetallic Assemblies with Ligands That Bridge Isolated Chromophores


The electrogenerated chemiluminescence (ECL) of [(bpy)2Ru]2(bphb)4+ (bphb = 1,4-bis(4′-methyl-2,2′-bipyridin-4-yl)benzene, bpy = 2,2′-bipyridine) and (bPy)2Ru-(bphb)2+ in acetonitrile (MeCN), 50:50 (v/v) MeCN/H2O, and aqueous solutions was studied. In both the mono-and bimetallic complexes, the ECL spectra are the same as the photoluminescence spectra, indicating the same metal-to-ligand charge-transfer states are formed in both ECL and photoluminescence. The bimetallic species produced more intense emission than Ru(bpy)32+ in all solvent mixtures when ECL was generated via annihilation and with the coreactant tri-n-propylamine, which generates a strong reductant on oxidation. Relative ECL efficiencies for [(bpy)2Ru]2(bphb)4+ were about 2-3 times that of Ru(bpy)32+ in MeCN and aqueous media. ECL was also generated with the coreactant S2O82-, which produces the strong oxidant SO42- upon reduction. However, the relative ECL efficiencies with S2O82- were smaller (0.6-0.8) relative to the Ru(bpy)32+. The monometallic species also displays ECL under the same conditions. However, the ECL intensity is dependent on both the solvent and the method of generating ECL. The mechanisms of ECL are discussed and digital simulation was employed to determine the most probable pathways for excited-state formation in the bimetallic species via the annihilation experiment. Because of their high ECL efficiencies, multimetallic systems of this type should be useful in the design of new labels for bioanalytical applications (e.g., immunoassays and DNA probes).

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Analytical Chemistry