The heteroleptic complexes containing 2,3-diphenylquinoline derivatives as phosphorescent materials Original Research Article

New types of heteroleptic iridium complexes were designed and synthesized with two different species of chelating ligands (C^N) in this study. Ir(ppy)2(4-Me-2,3-dpq), Ir(ppy)(4-Me-2,3-dpq)2, Ir(pq)2(4-Me-2,3-dpq) and Ir(pq)(4-Me-2,3-dpq)2 were prepared, where ppy, 4-Me-2,3-dpq and pq represent 2-phenylpyridine, 4-methyl-2,3-diphenylquinoline and 2-phenylquinoline, respectively. According to our previous study, Ir(4-Me-2,3-dpq)2(acac) showed orange-red emission at 603 nm with the luminescence efficiency of 8.10 cd/A in electroluminescence (EL) spectra. On the other hand, Ir(ppy)2(acac), a green phosphor, has been known to have an outstanding efficiency of more than 45 cd/A. In order to improve the luminescence efficiency, it is necessary to design a phosphorescent material which is capable of transferring the excited energy efficiently and properly. The heteroleptic Ir(III) complexes containing two different kinds of ligands can have a high luminescence efficiency by intramolecular energy transfer from the energy-absorbing ligand to the luminescent ligand, leading to a decrease in quenching or energy deactivation. Thus, the luminescence characteristics of the iridium complexes prepared herein were investigated. Ir(ppy)2(4-Me-2,3-dpq), Ir(ppy)(4-Me-2,3-dpq)2, Ir(pq)2(4-Me-2,3-dpq) and Ir(pq)(4-Me-2,3-dpq)2 exhibited the emission maxima at 512, 512, 583, and 584 nm, respectively. Two different light-emitting mechanisms were suggested to explain these phenomena.