Introduction of new ancillary ligands to the iridium complexes having 2,3-diphenylquinolinato ligands for OLED

We investigated the effect of an ancillary ligand (AL) on the emission color and luminous efficiencies of its complex, Ir(4-Me-2,3-dpq)2(AL), where 4-Me-2,3-dpq represents 4-methyl-2,3-diphenylquinolinato ligand. We expected that ancillary ligand modification by introduction of the bulky substituent to the complexes might allow luminous efficiency increase by reduction of T–T annihilation. Furthermore, some ancillary ligands may contribute to fine-tuning of their complex emission colors by influencing the energy level of Ir d-orbitals upon the orbital mixing. As new ancillary ligands substituting for acac which is a typical AL in the iridium complexes, pyrazolone-based ligands, 4-R-5-methyl-2-phenyl-2,4-dihydro-pyrazol-3-one series (przl-R), were prepared, where R represents C6H5, C6H4CH3 and C6H4Cl. These ligands were chelated to the iridium center to yield a new series of the iridium complexes, Ir(4-Me-2,3-dpq)2(przl-R). The X-ray crystal structure of Ir(4-Me-2,3-dpq)2(przl-C6H4Cl) was determined. The electrochemical and luminescence properties of the iridium complexes were investigated. The effect of the przl-substituents on the emission colors of the complexes was not significant. On the other hand, the luminous efficiencies of Ir(4-Me-2,3-dpq)2(przl-C6H5) and Ir(4-Me-2,3-dpq)2(przl-C6H4CH3) were higher than that of Ir(4-Me-2,3-dpq)2(acac).