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

Abstract

Two heteroleptic blue phosphorescent Ir(III) complexes are synthesized based on the main (CN)-N-boolean AND 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 center dot center dot center dot F and pi-pi 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.