Blue-Emitting Iridium(III) Carbene Phosphors with Suppressed Efficiency Roll-Off and Enhanced Durability of Hyper-OLED Devices

OLED technology has been long hampered by the slow progress of efficient and durable blue phosphors. To circumvent this issue, a novel imidazo[4,5-b]pyrazin-2-ylidene chelate with both the bulky tert-butyl and 2,6-dimethylphenyl appendages is rationally employed in synthesizing Ir(III) carbene phosphors f-ct8c and f-ct8d. Installation of bulky groups at the proper location not only reduces the anticipated product isomers to two, but also improves the photophysical efficiency of these Ir(III) emitters. Notably, these emitters exhibited blue photoluminescence with excellent quantum yields and short radiative lifetimes. One device with assistant sensitizer f-ct8c at 10 wt% and terminal emitter nu-DABNA at 1 wt% has successfully achieved a remarkable EQEmax of 30.5%, CIExy chromaticity of (0.129, 0.079), confirming the generation of exceptional blue hyperphosphorescence. Moreover, the same emitter f-ct8c co-doped in exciplex co-host of SiCzCz: SiTrzCz2 afforded EQEmax of 28.4% and EQE of 23.6% at practical luminance of 1000 cd m-2, respectively, together with max. luminance exceeding 27000 cd m-2. A long operational lifetime LT50 of 309 h is obtained for f-ct8d at an initial brightness of 500 cd m-2, affirming the improved efficiency and stability of the molecular designs.