A series of cyclometalated iridium(III) complexes ([Ir(pqcm)₂(bpy)][PF₆] (1), [Ir(pqcm)₂(dafo)[PF₆] (2), [Ir(pqcm)₂(phen)][PF₆] (3), [Ir(pqcm)₂(altpy)][PF₆] (4), [Ir(pqcm)₂(bbim)][PF₆] (5), [Ir(pqcm)₂(bvbbim)][PF₆] (6), pqcm=2-phenyl-quinoline-4-carboxylic acid methyl ester, bpy=2,2'-bipyridine, dafo=4,5-diazafluoren-9-one, phen=1,10-phenanthroline, altpy=4'-allyloxy-2,2':6',2''-terpyridine, bbim=2,2'-bibenzimidazole, bvbbim=1,1'-diallyl-2,2'-bibenz- imidazole) were synthesized with cyclometalated ligand of pqcm and N^N typical assistant ligands. New iridium(III) complexes were characterized by the NMR and mass spectroscopies, and the single crystal structure of complex 1 was measured, the cationic distorted octahedrally coordinated iridium(III) center was ligated by two cyclometalated pqcm ligands and one chelating bpy ligand with a negative [PF₆]^- counter anion. In CH₂Cl₂ solution, the iridium(III) complexes 1, 2 and 3 displayed orange red emissions with wavelength about 610 nm, while the iridium(III) complexes 4, 5 and 6 displayed pure red emissions with wavelength about 620 nm, which was desirable for example in organic light-emitting devices applications. The iridium(III) complexes had lifetimes between 133 ns and 496 ns, quantum efficiencies between 0.7% and 16.6%. All these iridium(III) complexes had higher quantum efficiencies than Ru(bpy)₃²⁺. The electrochemiluminescence (ECL) of cationic cyclometalated iridium complexes, immobilized on the glassy carbon electrode was investigated in neutral phosphate buffer solution (PBS). The ECL peaks were obtained when oxalate was used as co-reactant and positive initial potential scan direction was adopted. The ECL of iridium(III) complexes were different from that of Ru(bpy)₃²⁺, Iridium(III) complexes had higher ECL potential and more than three times higher ECL intensity than Ru(bpy)₃²⁺, suggesting that these synthesized iridium complexes have great application potential in ECL detection. Unlike Ru(bpy)₃²⁺, most iridium(III) complexes could not only offer intensive anodic ECL peak but also provide a cathodic ECL peak. The ECL intensities of iridium(III) complexes had almost the same sequence with the quantum efficiencies of iridium(III) complexes.

Key words: cyclometalated iridium(III) complex, 2-phenylquinoline, electrochemiluminescence (ECL)