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

Abstract

AbstractEfficient blue phosphors remain a formidable challenge 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, are synthesized, and their structures and photophysical properties are 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 the fabricated OLED devices, f‐ct6b delivers a max. external quantum efficiency (EQE) of 23.4% and Commission Internationale de L'Eclairage CIEx,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) exhibits max. EQE of 26.2% and CIEx,y of (0.12, 0.13). Finally, the corresponding tandem OLED with f‐ct6b as dopant gives a max. luminance of over 10 000 cd m−2 and max. EQE of 42.1%, confirming their candidacies for making true‐blue OLEDs.