Excited-State Modification of Phenylimidazole-Based Cyclometalated Ir(III) Complexes through Secondary Bulky Aryl Substitution and Inductive Modification Enhances the Blue Emission Efficiency in Phosphorescent OLEDs

• DOI: 10.1021/acs.inorgchem.2c02890
• Publication Date: 2022-11-08T21:50:33Z
• Authors: So-Yoen Kim; Jin-Hyoung Kim; Sanghun Lee; Bo-Sun Yun; Ho-Jin Son; Sang Ook Kang
• Keywords: Isopropyl; HOMO/LUMO; Terphenyl

To elucidate the key parameters governing emission properties of phenylimidazole (pim)-based Ir(III) emitters, including their electronic structure and bulky aryl substitution effect, a series pim-based iridium(III) complexes (Ir(Rpim-X)3, Rpim-X = 1-R-2-(X-phenyl)-1H-imidazole) bearing secondary pendants increasing bulkiness [R methyl (Me), phenyl (Ph), terphenyl (TPh), or 4-isopropyl (ITPh)] three different primary pim ligands (X F, F2, CN) were designed synthesized. Based on photophysical electrochemical analyses, it was found that excited state are highly dependent substituent inductive nature ligand. The incorporation TPh/ITPh substituents in second coordination sphere significantly enhanced efficiencies solid (ΦPL 72.1-84.9%) compared to those methyl- phenyl-substituted 30.4% for Ir(Mepim)3 63.7% Ir(Phpim)3). Further modification (Ir(TPhpim)3 → Ir(ITPhpim)3) through an isopropyl group F ligand (Ir(TPh/ITPhpim)3 Ir(TPh/ITPhpim-F/F2)3) resulted slight decrease LUMO significant HOMO energy levels, respectively; these level adjustments consequently amplified blue shifts, thereby enabling efficient electroluminescence phosphorescent organic light-emitting diodes. Theoretical calculations revealed excited-state can be modulated by peripheral presence EWG substituent. Among fabricated blue-emitting TPh/ITPh-substituted complexes, Ir(ITPhpim-F)3, Ir(TPhpim-F2)3, Ir(ITPhpim-F2)3 tested as dopants OLEDs owing high radiative quantum yields 75.9-84.9%). Ir(ITPhpim-F)3-doped multilayer device displayed best performance with maximum external efficiency 21.0%, current 43.6 cd/A, CIE coordinates 0.18 0.31.