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Ancillary ligand increases the efficiency of heteroleptic Ir-based triplet emitters in OLED devices
摘要： The excellent contrast ratio, visibility, and advantages in producing thin and light displays let organic light emitting diodes change the paradigm of the display industry. To improve future display technologies, higher electroluminescence efficiency is needed. Herein, the detailed study of the non-radiative decay mechanism employing density functional theory calculations is carried out and a simple, general strategy for the design of the ancillary ligand is formulated. It is shown that steric bulk properly directed towards the phenylisoquinoline ligands can significantly reduce the non-radiative decay rate.
关键词： photoluminescence quantum yield,non-radiative decay,OLED,Ir(III)-complexes,density functional theory
更新于2025-09-23 15:21:01
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Cyclometalated Ir(III) Complexes Towards Blue-Emissive Dopant for Organic Light-Emitting Diodes: Fundamentals of Photophysics and Designing Strategies
摘要： The main difficulties hindering development of a deep-blue phosphorescent cyclometalated Ir(III) complex are insufficient colour purity, i.e., failure to achieve ideal Commission Internationale de L’Eclairage (CIE) coordinates of (0.14, 0.09), and insufficient emission efficiency and stability. The latter problem is due to the highly energetic and hot excited states of these complexes, which yield faster decomposition. Therefore, control of the excited-state properties of cyclometalated Ir(III) complexes through systematic chemical modification of the ligands is being extensively investigated, with the aim of developing efficient and stable blue phosphorescent materials. The most common strategies towards achievement of a blue phosphorescent cyclometalated Ir(III) complex involve 1) substitution of electron-withdrawing F atoms at the cyclometalating ligands that stabilise the HOMO orbitals and 2) use of a heteropeltic system with electron-rich ancillary ligands bearing a 5-membered ring heterocycle to increase the LUMO energy level. However, the C–F bonds on the cyclometalating ligands have been found to be inherently unstable during device operation; thus, other types of electron-withdrawing groups (e.g., the cyano, trifluoromethyl, and sulfonyl groups) have been applied. Along with phosphorescence colour tuning to blue, the influence of the ligand structure on the photoluminescence quantum yield (PLQY) is also being intensively investigated. Two major PLQY lowering mechanisms for blue emissive Ir(III) complexes have been identified: 1) the vibronic-coupled non-radiative decay process and 2) crossing from the emissive state to an upper non-emissive 3MC excited state. To enhance the PLQY, mechanism 1) can be suppressed by employing rigid ligand frameworks to restrict intramolecular motion, whereas mechanism 2) can be prevented by destabilising the 3MC state using strong σ donor ligands such as N-heterocyclic carbenes. This review summarises the fundamental photophysics of cyclometalated Ir(III) complexes and surveys design strategies for efficient blue phosphorescent Ir(III) complexes, to provide a guide for future research in this field.
关键词： blue phosphorescent,3MC excited state,photoluminescence quantum yield,non-radiative decay,N-heterocyclic carbenes,cyclometalated Ir(III) complexes,OLEDs
更新于2025-09-23 15:21:01