Synthesis and luminescence study of red phosphorescent Ir(III) pyrazolonate complexes for OLED Original Research Article

A pyrazolone-based ligand, 4-acetyl-5-methyl-2-phenyl-2,4-dihydro-pyrazol-3-one (pyzl), was prepared and introduced as a new ancillary ligand, replacing acac in the iridium complexes for high efficient OLED. The purpose of this study was that modification of the ancillary ligand might allow luminous efficiency increase by reducing T–T annihilation. The przl ligand in the iridium complex might also lead to fine tuning of the emission color by affecting the energy level of Ir d-orbitals. Previously, we reported that the iridium complexes, Ir(4-Me-2,3-dpq)2(acac) and Ir(2,3-dpqx-F2)2(acac), exhibited their electroluminescence (EL) emission at 603 and 630 nm with luminous efficiency of 8.10 and 2.75 cd/A, respectively, where 6-Me-2,3-dpq, 2,3-dpqx-F2 and acac represent 4-methyl-2,3-diphenylquinoline and 2,3-bis-(4-fluorophenyl)quinoxaline and acetylacetonate, respectively. In this study, we synthesized a new series of iridium complexes with the pyrazolonate ligand, Ir(6-Me-2,3-dpq)2(przl) and Ir(2,3-dpqx-F2)2(przl), and investigated their luminescence properties with respect to the involvement of a new bulky ancillary ligand, przl, compared with the complexes containing the ligand acac.