Xu Yuwei, Liang Xiaoming, Liang Yiqian, Guo Xiaomin, Hanif Muddasir, Zhou Jiadong, Zhou Xuehong, Wang Cong, Yao Jingwen, Zhao Ruiyang, Hu Dehua, Qiao Xianfeng, Ma Dongge, Ma Yuguang
Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices , South China University of Technology , Guangzhou 510640 , P. R. China.
College of Chemical Engineering , Qingdao University of Science and Technology , Qingdao 266042 , P. R. China.
ACS Appl Mater Interfaces. 2019 Aug 28;11(34):31139-31146. doi: 10.1021/acsami.9b10823. Epub 2019 Aug 15.
A novel, efficient, deep-blue fluorescent emitter mPAC, with a meta-connected donor-acceptor structure containing phenanthroimidazole (PPI) as the donor and phenylcarbazole-substituted anthracene (An-CzP) as the acceptor, was designed and synthesized. The meta-linkage provided a highly twisted molecular conformation, which efficiently interrupts the intramolecular π-conjugation, resulting in a deep-blue emission. The optimized nondoped device based on mPAC displayed a deep-blue emission with a narrow full width at half-maximum of 56 nm and Commission Internationale de L'Eclairage coordinates of (0.16, 0.09). The maximum external quantum efficiency (EQE) is 6.76%, corresponding to a high exciton utilization efficiency (EUE) of 59.3-88.9%. Experimental results and theoretical analysis indicated that the high EUE is mainly ascribed to the reverse intersystem crossing (RISC) from T to S, a "hot exciton" path in which the large T-T energy gap (1.45 eV) and small T-S energy difference (0.18 eV, T > S) hamper the internal crossing from T to T and facilitate the RISC process. For the hot exciton path, the T state can be feasibly arranged to a high energy level, forming a thermal equilibrium with S, even slightly higher than the deep-blue S to realize an exergonic RISC process, which is usually difficult for the thermally activated delayed fluorescence emitters.
设计并合成了一种新型高效的深蓝色荧光发射体mPAC，其具有间位连接的供体-受体结构，包含菲并咪唑（PPI）作为供体和苯基咔唑取代的蒽（An-CzP）作为受体。间位连接提供了高度扭曲的分子构象，有效地中断了分子内的π共轭，从而产生深蓝色发射。基于mPAC的优化非掺杂器件显示出深蓝色发射，半高宽为56 nm，国际照明委员会坐标为（0.16, 0.09）。最大外量子效率（EQE）为6.76%，对应于59.3 - 88.9%的高激子利用效率（EUE）。实验结果和理论分析表明，高EUE主要归因于从T到S的反向系间窜越（RISC），这是一条“热激子”路径，其中较大的T - T能隙（1.45 eV）和较小的T - S能量差（0.18 eV，T > S）阻碍了从T到T的内转换，并促进了RISC过程。对于热激子路径，T态可以被合理地排列到高能级，与S形成热平衡，甚至略高于深蓝色的S，以实现一个放能的RISC过程，这对于热激活延迟荧光发射体来说通常是困难的。
