The Synthesis And Electroluminescent Properties Of Iridium(?) Cyclometalated Complexes Containing Sterically Hindered Ligands

Owning to the d6 electron configuration of iridium(?)ion,neutral cyclometalated iridium(?)complexes with six chemical bonds adoptn octahedral molecular conformation.The strong spin orbit coupling,which originate from iridium(?)ions to cyclometalating ligands,the quantum efficiency of iridium(?)complexes can theoretically reach 100%.Phosphorescent organic light-emitting diodes(PhOLEDs)based on cyclometalated iridium(?)complexes have attracted enormous attention for potential use in full-color flat-panel display and solid-state light source.In this paper,the cyclometalating ligands SFXpy and SFXbtz were successfully synthesized by a simple "one-pot" Friedel-Crafts cyclization and Suzuki-Miyaura coupling reaction.Based on thise two ligands,Ir(SFXpy)3 and Ir(SFXbtz)3 complexes were obtained by "one-step" method using Ir(acac)3 as the precursor.Single crystal X-ray analysis of the resulting Ir(SFXpy)3 and Ir(SFXbtz)3 complexs revealed enlarged Ir···Ir distance and negligible intermolecular ?-? interactions in between the spiro ligands.The emitter exhibits yellow emission and almost equal energy levels compared to the commercial phosphor iridium(?)bis(4-phenylthieno[3,2-c]pyridinato-N,C2?)acetylacetonate(PO-01).Dry-processed devices using a common host 4,4?-bis(N-carbazolyl)-1,1?-biphenyl(CBP)and the Ir(SFXpy)3 emitter at a doping concentration of 15 wt% exhibited a peak performance of 46.2 cd A–1,36.3 lm W–1,and 12.1% for current efficiency(CE),power efficiency(PE),and external quantum efficiency(EQE),respectively.The superior performance of the new emitter-based devices was ascribed to key roles of spiro ligand for suppressing aggregation and assisting charge carrier injection/transport.Benefited from the amorphous stability of the emitter,the wet-processed device also exhibited excellent CE,PE,and EQE of 32.2 cd A–1,22.1 lm W–1,and 11.3%,respectively,while the EQE roll-off was as low as 1.7% at the luminance of 1000 cd m–2.The three-dimensional geometry and binary-conjugation features renders SFX the ideal multifunctional module for suppressing concentration quenching,facilitating charge carrier injection/transport,and improving amorphous stability of Ir?-based phosphorescent emitters.