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

Abstract

New types of heteroleptic iridium complexes were designed and synthesized with two different species of chelating ligands (C boolean AND 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 otherhand, 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. (C) 2007 Elsevier Ltd. All rights reserved.