Yang Jian-Gong, Song Xiu-Fang, Wang Jian, Li Kai, Chang Xiaoyong, Tan Li-Ying, Liu Chu-Xuan, Yu Fei-Hu, Cui Ganglong, Cheng Gang, To Wai-Pong, Yang Chuluo, Che Chi-Ming, Chen Yong
Key Laboratory of Photochemical Conversion and Optoelectronic Materials &, CAS-HKU Joint Laboratory on New Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing, 100190, P. R. China.
College of Materials Science and Engineering, Shenzhen University, Shenzhen, 518055, P. R. China.
Chemistry. 2021 Dec 20;27(71):17834-17842. doi: 10.1002/chem.202102969. Epub 2021 Nov 12.
Metal-based thermally activated delayed fluorescence (TADF) is conceived to inherit the advantages of both phosphorescent metal complexes and purely organic TADF compounds for high-performance electroluminescence. Herein a panel of new TADF Au(I) emitters has been designed and synthesized by using carbazole and pyrazine-fused nitrogen-heterocyclic carbene (NHC) as the donor and acceptor ligands, respectively. Single-crystal X-ray structures show linear molecular shape and coplanar arrangement of the donor and acceptor with small dihedral angles of <6.5°. The coplanar orientation and appropriate separation of the HOMO and LUMO in this type of molecules favour the formation of charge-transfer excited state with appreciable oscillator strength. Together with a minor but essential heavy atom effect of Au ion, the complexes in doped films exhibit highly efficient (Φ∼0.9) and short-lived (<1 μs) green emissions via TADF. Computational studies on this class of emitters have been performed to decipher the key reverse intersystem crossing (RISC) pathway. In addition to a small energy splitting between the lowest singlet and triplet excited states (ΔE ), the spin-orbit coupling (SOC) effect is found to be larger at a specific torsion angle between the donor and acceptor planes which favours the RISC process the most. This work provides an alternative molecular design to TADF Au(I) carbene emitters for OLED application.
基于金属的热激活延迟荧光（TADF）被认为继承了磷光金属配合物和纯有机TADF化合物的优点，可用于高性能电致发光。在此，通过分别使用咔唑和吡嗪稠合的氮杂环卡宾（NHC）作为供体和受体配体，设计并合成了一组新型TADF金（I）发射体。单晶X射线结构显示出线性分子形状以及供体和受体的共面排列，二面角小于6.5°。这种分子中HOMO和LUMO的共面取向和适当分离有利于形成具有可观振子强度的电荷转移激发态。再加上金离子较小但必不可少的重原子效应，掺杂薄膜中的配合物通过TADF表现出高效（Φ∼0.9）且短寿命（<1μs）的绿色发射。已对这类发射体进行了计算研究，以解读关键的反向系间窜越（RISC）途径。除了最低单重态和三重态激发态之间的小能量分裂（ΔE）外，还发现自旋轨道耦合（SOC）效应在供体和受体平面之间的特定扭转角处更大，这最有利于RISC过程。这项工作为用于OLED应用的TADF金（I）卡宾发射体提供了一种替代分子设计。
