Charge-Neutral Ir(III) Metal Phosphors Bearing Functional Pyrazole-Pyridine-Pyrazole Chelates

Homoleptic charge-neutral Ir(III) metal complexes bearingtridentatechelates composed of two orthogonally aligned pyrazole-pyridine-pyrazolefragments were designed and synthesized. It is notable that the substituentsplay an essential role in tuning both the photophysical and electrochemicalproperties. Upon the introduction of CF3 substituents atthe central pyridyl fragment of one tridentate chelate and peripheralpyrazolate fragments of alternative tridentate chelate, phosphorescencecan be fine-tuned from green to orange, together with an improvedemission quantum yield, as recorded in degassed tetrahydrofuran (THF)solution at room temperature (RT). Further replacement of the N-Hfragment of monoanionic chelate with a methyl substituent gives Ir(III)complexes [Ir((B)pz2pyMe)((F)pz2py)] (2Me) and [Ir((B)pz2(F)pyMe)((F)pz2py)] (3Me), showing decomposition temperatures (T (d)) greater than 300 & DEG;C. Therefore, this work pavesa new avenue for designing and synthesizing emissive Ir(III) complexeswithout the traditional cyclometalating aromatics, albeit with a loweredemission efficiency. As a proof of concept, Ir(III) complexes 2Me and 3Me were employed as the dopant emittersfor organic light-emitting diode (OLED) fabrication, giving a maximumexternal quantum efficiency (EQE) of 7.1 and 15.9% and a current efficiency(CE) of 22.5 and 50 cd & BULL;A(-1), respectively.

Automated summary

Homoleptic charge-neutral Ir(III) metal complexes with tridentate chelates composed of pyrazole-pyridine-pyrazolefragments were synthesized, and the substituents on the chelate played a significant role in tuning their photophysical and electrochemical properties. By introducing CF3 substituents at specific positions, the phosphorescence color of the complexes could be adjusted from green to orange with improved emission quantum yield. The newly synthesized Ir(III) complexes showed high thermal stability and were applied as dopant emitters in OLEDs, exhibiting high external quantum efficiency and current efficiency.