Efficient blue, green and red iridium() complexes with noncovalently-linked pyrazole/pyrazolide rings for organic light-emitting diodes

Noncovalently-linked rings are broadly employed to construct highly planar semiconductors exhibiting substantial electron and hole transport characteristics. In this paper, three cyclometalated iridium( iii ) complexes with blue, green and red emissions ( B-Ir1-H , G-Ir2-H and R-Ir3-H ) using 2-(2,4-difluorophenyl)pyridine, 2-(4-(trifluoromethyl)phenyl)pyridine and 4-(4-(trifluoromethyl)phenyl)quinazoline as main ligands, respectively, and dipyrazole as the ancillary ligand containing the nitrogen-hydrogen N-H-N bond were synthesized with an absolute phosphorescence quantum efficiency of 0.66, 0.55 and 0.38 in degassed CH 2 Cl 2 solution, respectively. The iridium complex adopts a distorted octahedral coordination geometry, and the Ir-N-N H-N-N heterocycle exhibits a planar conformation, with a slight twist between the N-Ir1-N plane and two adjacent N-N-H planes, and its dihedral angles are about −5.8 and 7.6°, respectively. Moreover, the organic light-emitting diodes (OLEDs) with the configuration of ITO/HATCN (hexaazatriphenylenehexacabonitrile, 5 nm)/TAPC (bis(4-( N , N -ditolylamino)phenyl)-cyclohexane, 30 nm)/Ir( iii ) complex ( x wt%): 2,6-DCzPPy (2,6-bis-(3-(carbazol-9-yl)phenyl)pyridine, 10 nm)/TmPyPB (1,3,5-tri((3-pyridyl)-phen-3-yl)benzene, 40 nm)/LiF (1 nm)/Al (100 nm) ( x wt% = 6, 8 and 2 wt%, respectively) show different performances. The green device displays the best performance showing a maximum luminance of 36 020 cd m −2 , a maximum current efficiency of 53.8 cd A −1 and a maximum external quantum efficiency of 21.0%, respectively, with low efficiency roll-off. The EQE could still be kept at 20.7% even at the high brightness of 5000 cd m −2 . These results indicate that the ancillary ligands with noncovalently-linked rings might provide a new pathway for constructing highly efficient phosphorescent emitters for OLEDs. Blue, green and red iridium( iii ) complexes using a new pyrazole/pyrazolide ancillary ligand system, and their application in OLEDs with EQEs of up to 21.0% and low efficiency roll-off.