Blue Electrophosphorescence from Iridium(III) Phosphors Bearing Asymmetric Di-N-Aryl 6-(trifluoromethyl)-2H-imidazo[4,5-b]pyridin-2-ylidene Chelates.

Efficient blue phosphors remain as the formidable challenges for organic light-emitting diodes (OLEDs). To circumvent this obstacle, a series of Ir(III) based carbene complexes bearing asymmetric di-N-aryl 6-(trifluoromethyl)-2H-imidazo[4,5-b]pyridin-2-ylidene chelates, namely, f-ct6a - c, were synthesized and their structures and photophysical properties were comprehensively investigated. Moreover, these emitters can undergo interconversion in refluxing 1,2,4-trichlorobenzene, catalyzed by a mixture of sodium acetate (NaOAc) and p-toluenesulfonic acid monohydrate (TsOH·H2O) without decomposition. All Ir(III) complexes present good photoluminescence quantum yield (ΦPL = 83 - 88%) with peak maximum (max.) at 443 - 452 nm and narrowed full width at half maximum (FWHM = 66 - 73 nm). Among all fabricated OLED devices, f-ct6b delivered a max. external quantum efficiency (EQE) of 23.4% and Commission Internationale de L'Eclairage CIE(x,y) coordinates of (0.14, 0.12), whereas the hyper-OLED device based on f-ct6a and 5H,9H,11H,15H-[1,4] benzazaborino [2,3,4-kl][1,4]benzazaborino[4',3',2':4,5][1,4]benzazaborino[3,2-b]phenazaborine-7,13-diamine, N7,N7,N13,N13,5,9,11,15-octaphenyl (ν-DABNA) exhibited max. EQE of 26.2% and CIE(x,y) of (0.12, 0.13). Finally, the corresponding tandem OLED with f-ct6b as dopant gave a max. luminance of over 10000 cd⋅m-2 and max. EQE of 42.1%, confirming their candidacies for making true-blue OLEDs. This article is protected by copyright. All rights reserved.