Blue Electrophosphorescence from Iridium(III) Phosphors Bearing Asymmetric Di‐<i>N</i>‐aryl 6‐(trifluoromethyl)‐2<i>H</i>‐imidazo[4,5‐b]pyridin‐2‐ylidene Chelates
Jie Yan, Ziqi Feng, Yixin Wu, Dong‐Ying Zhou, Shek‐Man Yiu, Chin‐Yiu Chan, Yi Pan, Kai‐Chung Lau, Liang‐Sheng Liao, Yün Chi
Abstract
Abstract Efficient 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·H 2 O) without decomposition. All Ir(III) complexes present good photoluminescence quantum yield ( Φ PL = 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 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) exhibits max. EQE of 26.2% and CIE x , 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.