Enhanced Electrogenerated Chemiluminescence of ruthenium and iridium coordination compounds using melatonin

Enhanced Electrogenerated Chemiluminescence (ECL) is observed in a series of iridium and ruthenium systems when melatonin is present in solution. The mechanism involves oxygen scavenging by the products of melatonin electrochemical oxidation, thus preventing oxygen from quenching the ECL excited states. [Display omitted] •Enhanced coreactant Electrogenerated Chemiluminescence when melatonin is present in solution.•Melatonin oxidation products interact with dissolved oxygen to prevent excited state quenching. The effect on the coreactant Electrogenerated Chemiluminescence (ECL) of (bpy)2Ru(DC-bpy)2+ (bpy=2,2′-bipyridine and DC-bpy=4,4′-dicarboxy-2,2′-bipyridine), (bpy)2Ru(DM-bpy)2+ (DM-bpy=4,4′-dimethyl-2,2′-bipyridine), and Ir(ppy)3 (ppy=2-phenylpyridine) when melatonin (N-acetyl-5-methoxytryptamine; MLT) is present in aqueous buffered solution is reported with tri-n-propylamine as the coreactant. Micromolar concentrations of melatonin generate up to 1.4-fold enhancement of (bpy)2Ru(DC-bpy)2+/TPrA ECL and (bpy)2Ru(DM-bpy)2+/TPrA ECL, and 1.7-fold enhancement Ir(ppy)3/TPrA ECL. Photoluminescence (PL) emission efficiencies and spectra do not change in the presence of melatonin unless the melatonin solution has undergone electrochemical bulk oxidation, at which point PL and ECL are nearly indistinguishable. Electrochemical and spectroscopic experiments indicate that the mechanism involves the scavenging of oxygen by melatonin oxidation products that prevents the quenching of excited states by dissolved oxygen in solution.