Efficient red-emitting phosphorescent iridium(III) complexes of fluorinated 2,4-diphenylquinolines

Ir(β) complexes of fluorinated dpqs(dpq-3-F, dpq-4-CF3) as a cyclometallated ligand were prepared and their photonic properties were investigated, where dpq-3-F and dpq-4-CF3 represent 2-(3-fluoro-phenyl)-4-phenylquinoline and 4-phenyl-2-(4-trifluoromethylphenyl)quinoline, respectively. Fluorinated dpq derivatives were introduced to the iridium complexes to increase the efficiency compared to Ir(dpq)2(acac) which was recently reported to have emission wavelength of 614 nm with quantum efficiency of 0.14. These fluorinated ligands and their Ir(III) complexes were computationally calculated by ab initio methods to support our experimental results. It was found that the Ir complex containing dpq-3-F ligands exhibits the largest emission efficiency with maximum emission peak at 593.5 nm. The result of ab initio calculation using the time-dependent density functional theory (TD-DFT) showed that the strong 3MLCT transition of the complex occurs due to the strong coupling between the 5d orbital of the Ir atom and the highest occupied molecular orbitals (HOMOs) of these ligands.