Peripheral Engineering of Ir(iii) Emitters with Imidazo[4,5-B]pyrazin-2-ylidene Cyclometalates for Blue Organic Light Emitting Diodes

Ir(iii) based carbene complexes are highly sought after in the field of organic light-emitting diodes (OLEDs), as they are expected to solve the thorny issue of efficient and durable blue phosphors. Hence, three tris-bidentate Ir(iii) based carbene complexes, namely, f-ct4a-c, were synthesized and fully characterized by both spectroscopic and structural methods, presenting a bulky 2,6-dimethylphenyl substituent on the imidazo[4,5-b]pyrazin-2-ylidene fragment, and a distinctive N-aryl (i.e., either phenyl or 4-t-butylphenyl) appendage and cyclometalating group. These complexes exhibited sky-blue emission with a peak max. located between 473 and 482 nm and a photoluminescent quantum yield (PLQY) of 50-68% recorded in degassed toluene, and furthermore, a much-improved PLQY of 71-87% upon doping in the 2,8-bis(diphenylphosphoryl)dibenzo[b,d]thiophene (PPT) host matrix. Remarkably, the f-ct4b based OLED device and respective hyper-OLED device exhibited blue Commission Internationale de L'Eclairage CIEx,y coordinates of (0.19,0.47) and (0.11,0.44), and max. external quantum efficiencies (EQEs) of 17.4% and 21.5%, respectively, demonstrating their potential in future OLED applications.