2-Phenylpyridine-based phosphorescent Ir(III) complexes for highly efficient greenish-blue organic light-emitting diodes with EQEs up to 33.5%

A group of heteroleptic cyclometalated iridium complexes Ir1-Ir4 were designed with 2-phenylpyridine (ppy) derivatives as cyclometalating ligands and 2-(3-(trifluoromethyl)-1H-pyrazol-5-yl)pyridine (fppz) or 2-(5-(4(trifluoromethyl)phenyl)-2H-1,2,4-triazol-3-yl)pyridine (Htaz) as ancillary ligands. The incorporation of electrodonating group into ppy ligands to elevate ligands-centered 3 pi-pi* energy level and utilization of fppz or Htaz ancillary ligands combined to tune the intrinsic electronic properties. These complexes showed greenish-blue or green phosphorescence and are characterized by high photoluminescence quantum yields of up to 70% and short lifetimes below 1 mu s. The organic light-emitting diodes (OLEDs) with Ir1-Ir4 as doped emitters all exhibited high efficiencies with low efficiency roll-off. Particularly, the Ir3 device exhibited distinguished performances with the maximum current efficiency of 86.9 cd A-1 and an external quantum efficiency (EQE) of 33.5%. Even at high brightness of 1000 cd m- 2, the EQE still remained at 24.6%. Evidently the EQE of 33.5% of Ir3 device is one of the highest efficiencies ever reported for greenish-blue phosphorescence OLEDs.