Electrogenerated chemiluminescence of a cationic cyclometalated iridium complex–Nafion modified electrode in neutral aqueous solution

Abstract

Electrogenerated chemiluminescence (ECL) of a cationic cyclometalated iridium complex, [(pqcm)2Ir(bpy)](PF6) (1, pqcmH=2-phenyl-quinoline-4-carboxylic acid methyl ester, bpy=2,2′-bipyridine), was investigated at a bare glassy carbon electrode in CH3CN solution and 4 ECL peaks were observed. Then, the ECL of the iridium complex was studied in neutral phosphate buffer solution (PBS) by immobilizing it on a glassy carbon electrode. Two closely located ECL peaks were obtained at 1.07 and 1.40V when the potential was scanned from −3.00V to 2.20V, while only one broad ECL peak located around −2.0V was obtained when the potential was scanned from 2.20V to −3.00V. In the presence of oxalate, one ECL peak located around 1.22V could be obtained except the broad ECL peak located at −2.00V. The ECL peak at positive potential range was enhanced more than one magnitude in the presence of Nafion and was nearly 5-times higher than that of Ru(bpy)32+–Nafion modified electrode, suggesting that the synthesized iridium complex has great application potential in ECL detection. The ECL spectra of iridium complex were identical to its photoluminescence spectrum, indicating the same metal-to-ligand charge transfer (MLCT) excited states. The mechanisms of ECL were proposed based on the experimental results. The present ECL sensor gave a linear response for the oxalate concentration from 1.0×10−6 to 1.0×10−4molL−1 with a detection limit (S/N=3) of 9.1×10−7molL−1.