Blue Phosphorescent Ir(III) Complexes Achieved with Over 30% External Quantum Efficiency

Two heteroleptic blue phosphorescent Ir(III) complexes are synthesized based on the main C^{^}N chelate bipyridine ligands, with either a 4-positon (1) or 5-position (2) of bulky trimethylsilyl (TMS) substituent, and acetylacetonate (acac) as an ancillary ligand. Their structure–electroluminescent property relationships are systematically investigated. Both complexes have strong intermolecular interactions via C–H···F and π–π interactions that affect the performance of phosphorescent organic light-emitting diodes (PHOLEDs). Complex 1 possesses fewer intermolecular interactions than complex 2 based on the Hirshfeld analysis. The combination of TMS substituent and acac ligand decreases the energy gap relative to the nonsubstituted counterpart: Ir(dfpypy)(acac), where dfpypy is 2′-6′-difluoro-2,3′-bipyridine. Blue PHOLEDs which use both complexes as a dopant, and 9-(3-(9H-carbazol-9-yl)phenyl)-9H-carbazol-3-yl)diphenylphosphine oxide as a host material, are fabricated successfully. Complex 1 has the highest performance among the reported blue PHOLEDs without co-host, making it an outstanding blue triplet emitter in PHOLEDs with over 30% of external quantum efficiency. Furthermore, the efficiency roll-off dramatically improved in the 1-based device.