Highly efficient solution processed OLEDs based on iridium complexes with steric phenylpyridazine derivative

Abstract

Four bis-cyclometalated iridium complexes (Ir(tpp)2(pic) (1), Ir(tpp)2(paz) (2), (Ir(ttp)2(pic) (3) and (Ir(ttp)2(paz) (4) with phenylpyridazine derivative ligands were synthesized under mild reaction conditions, in which tpp (tppH = 3, 6-bis(4- (trifluoromethyl)phenyl)pyridazine) or ttp (ttpH = (5 s, 8 s)-1,4-bis(4- (trifluoromethyl))-diphenyl-5,6,7,8-tetrahydro-5,8-thanophthalazine) was used as the primary ligand and pyridine-2-carboxylate (pic) or paz (pazH = 2-(3-(trifluoromethyl)-1H-pyrazol-5-yl)pyridine) were used as ancillary ligand. The coordination arrangement of complexes 1–3 was revealed by the single X-ray structural analyses. All complexes showed strong emissions with peaks ranged from 519 to 547 nm and quantum efficiencies of 0.55–0.80. By introducing sterically hindered bicyclo [2.2.2] oct-2-ene groups in the primary ligands of complexes 3 and 4, their molecular interactions are strongly restrained in solid. The organic light-emitting diodes (OLEDs) were fabricated with complexes 2 (device A) and 4 (device B) as dopants. The better device performances with a maximum current efficiency of 50.5 cd A−1 and a maximum external quantum efficiency of 14.9% are achieved by device B, along with smaller efficiency roll-off, which is attributed to the effect of alkyl steric groups and relative more matched energy levels in device.