Highly efficient electrochemiluminescence from iridium(III) complexes with 2-phenylquinoline ligand

A series of cyclometalated iridium(III) complexes with 2-phenylquinoline ligand (1-4) were designed and synthesized, which were thoroughly investigated by the photophysics, electrochemistry, theoretical calculations and electrochemiluminescence (ECL). By incorporating methyl groups into the 2-phenylquinoline, the corresponding complexes 2 and 3 displayed lower oxidative potential and higher HOMO energy levels. Most importantly, compared with tris(2,2'-bipyridyl)ruthenium(II) ([Ru(bipy)(3)](2+)), these iridium(III) complexes demonstrated more intense ECL in acetonitrile solutions.