Regioselective Syntheses of Imidazo[4,5- b ]pyrazin-2-ylidene-Based Chelates and Blue Emissive Iridium(III) Phosphors for Solution-Processed OLEDs.

Six homoleptic Ir(III) complexes bearing imidazo[4,5- b ]pyrazin-2-ylidene chelates were successfully designed and synthesized. Narrowband blue emission (λ max = 466-485 nm) and broadened green emission (λ max = 518-532 nm) in degassed toluene solution with high photoluminescent quantum yields in the range of 75-81 and 45-48% were observed for f -timpz , t2impz , and t2empz as well as m -timpz , t2impz , and t2empz , respectively. In addition, the tert -butylphenyl cyclometalate is more electron donating than N -phenyl cyclometalate and, hence, all tert -butylphenyl-substituted derivatives, that is, m - and f -t2impz and m - and f -t2empz , give more red-shifted emission in comparison to that of m - and f -timpz . Moreover, solution-processed OLED with f -t2empz (20 wt %) as the dopant gave electrophosphorescence at 474 nm with maximum external quantum efficiency (max. EQE) of 5.1%, while hyper-OLED with assistant sensitizer f -t2empz (10 wt %) and the multi-resonance thermally activated delayed fluorescence emitter BCzBN (0.5 wt %) afforded narrowband emission centered at 485 nm and max. EQE up to 17.4%, confirming the high potential of this class of Ir(III) metal phosphors.