Asymmetric [Ir(C^N)(C^N)(L^X)]-tris-heteroleptic iridium() complexes enable deep blue phosphorescent emission

• Published in: New journal of chemistry 2023-10, Vol.47 (4), p.1863-1869
• Main Authors: Gu, Li, Li, Shuaibing, Han, Huabo, Wang, Xinzhong, Zhou, Changjiang, Lu, Junjian, Zhou, Liang, Lu, Guangzhao
• Format: Article
• Language: English
• Subjects: Asymmetry; Configurations; Density functional theory; Dichloromethane; Iridium compounds; Isomers; Ligands; Mathematical analysis; Molecular orbitals; Phosphorescence; Photoluminescence; Quantum efficiency
• ISSN: 1144-0546; 1369-9261
• DOI: 10.1039/d3nj03513a

Three novel blue iridium( iii ) complexes, namely Ir(medfppy) 2 (fptz) ( Ir-mm ), Ir(dfbpy)(medfppy)(fptz) ( Ir-dm ), and Ir(medfppy)(dfbpy)(fptz) ( Ir-md ), were prepared and characterized by adopting a new [Ir(C 1 ^N 1 )(C 2 ^N 2 )(LX)]-tris-heteroleptic Ir( iii ) configuration, where C 1 ^N 1 and C 2 ^N 2 denote two different main ligands and LX denotes a third ancillary ligand. These three complexes exhibited exclusively blue emission peaks from 446 to 454 nm, with high photoluminescence quantum yields (PLQYs) of up to 48% and short decay lifetimes ranging from 0.42 to 2.63 μs in degassed CH 2 Cl 2 solutions. Density function theory (DFT) calculations showed that the resultant asymmetric isomers, Ir-dm and Ir-md , possessed quite different frontier molecular orbitals when the ligand medfppy in the symmetric complex Ir-mm was replaced by the stronger electron-withdrawing ligand dfbpy. Time-dependent DFT (TD-DFT) calculations suggested that the lowest triplet excited states of the isomers were dominated by the hole-particle transitions and the contributions of ligand-centered transitions (LC) were all higher than 78% for the three complexes. Phosphorescent blue OLEDs based on these complexes exhibited the maximum external quantum efficiencies (EQE max ) of up to 10.2% with the Commission Internationale de l'Eclairage (CIE) coordinates of (0.17, 0.24). This study presents the creative application of tris-heteroleptic configuration to blue iridium complexes for efficient OLEDs. One bis-cyclometalated blue iridium complex and two tris-heteroleptic blue iridium isomers containing the asymmetric tris-heteroleptic [Ir(C 1 ^N 1 )(C 2 ^N 2 )(LX)]-configuration are developed and applied in OLEDs with good EL performances.