Iridium(iii) complexes adopting 1,2-diphenyl-1H-benzoimidazole ligands for highly efficient organic light-emitting diodes with low efficiency roll-off and non-doped feature

Abstract

Two novel iridium(III) complexes (pbi)₂Ir(mtpy) (1) and (pbi)₂Ir(pbim) (2) adopting 1,2-diphenyl-1H-benzoimidazole (Hpbi) as cyclometalated ligands were successfully synthesized and characterized. Strong emissions at 501 and 536 nm with high photoluminescence quantum yields of 48% and 91% in CH₂Cl₂ at 298 K were obtained for 1 and 2, respectively. The quantum chemical calculations and the photophysical properties indicated that the dominant ³MLCT (metal-to-ligand charge-transfer) state mixed with ³LLCT (ligand-to-ligand charge-transfer) and ³LC (ligand-centered ³π–π*) characters contributed to their phosphorescence emissions. Doped organic light-emitting diodes (OLEDs) based on 1 and 2 showed a peak current efficiency of 45.0 cd A⁻¹ and power efficiency of 47.9 lm W⁻¹ accompanied by very low efficiency roll-off values. In their non-doped OLEDs, high efficiencies of 24.4 cd A⁻¹ and 26.3 lm W⁻¹ were achieved as well. These appealing results reveal that complexes 1 and 2 open interesting perspectives for the development of high-performance OLEDs in the future.