Hu Yeqian, Tang Xiantong, Pan Ruiheng, Deng Jinqiu, Zhu Hongqiang, Xiong Zuhong
School of Physical Science and Technology, MOE Key Laboratory on Luminescence and Real-Time Analysis, Southwest University, Chongqing 400715, People's Republic of China.
Phys Chem Chem Phys. 2019 Aug 15;21(32):17673-17686. doi: 10.1039/c9cp01201j.
The thermally activated delayed fluorescence (TADF) material 2,3,5,6-tetrakis(3,6-diphenylcarbazol-9-yl)-1,4-dicyanobenzene (4CzTPN-Ph) and the conventional fluorescent dopant 4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidin-4-yl-vinyl)-4H-pyran (DCJTB) were used to co-dope the host material 4,4'-bis(carbazol-9-yl)biphenyl (CBP) for the fabrication of TADF-assisted fluorescent organic light-emitting diodes (OLEDs). Some exceptional magnetic field effect (MFE) curves with abundant structures and four tunable components within a low magnetic field range (≤50 mT) were obtained, in sharp contrast to the maximum of two components observed in typical OLEDs. These MFE components were easily tuned by the injection current, dopant concentration, working temperature, and dopant energy gap, leading to a wide variety of MFE curve line shapes. The experimental results are attributed to the spin-pair state inter-conversions occurring in the device, including intersystem crossing (ISC) of CBP polaron pairs, ISC of 4CzTPN-Ph polaron pairs, reverse ISC (RISC) of 4CzTPN-Ph excitons, RISC of DCJTB polaron pairs, DCJTB triplet fusion, and DCJTB triplet-charge annihilation. Moreover, the exciton energy transfer processes among the host material and the guest dopants had a pronounced impact on the formation of these four components. This work gives a deeper understanding of the microscopic mechanisms of TADF-based co-doped systems for the further development of organic magnetic field effects in the extensive field of OLEDs.
采用热激活延迟荧光（TADF）材料2,3,5,6-四（3,6-二苯基咔唑-9-基）-1,4-二氰基苯（4CzTPN-Ph）和传统荧光掺杂剂4-（二氰基亚甲基）-2-叔丁基-6-（1,1,7,7-四甲基朱利啶-4-基乙烯基）-4H-吡喃（DCJTB）共掺杂主体材料4,4'-双（咔唑-9-基）联苯（CBP），用于制备TADF辅助荧光有机发光二极管（OLED）。在低磁场范围（≤50 mT）内获得了一些具有丰富结构和四个可调谐成分的特殊磁场效应（MFE）曲线，这与典型OLED中观察到的最多两个成分形成鲜明对比。这些MFE成分很容易通过注入电流、掺杂剂浓度、工作温度和掺杂剂能隙进行调节，从而产生各种各样的MFE曲线形状。实验结果归因于器件中发生的自旋对状态相互转换，包括CBP极化子对的系间窜越（ISC）、4CzTPN-Ph极化子对的ISC、4CzTPN-Ph激子的反向ISC（RISC）、DCJTB极化子对的RISC、DCJTB三重态融合和DCJTB三重态-电荷湮灭。此外，主体材料和客体掺杂剂之间的激子能量转移过程对这四个成分的形成有显著影响。这项工作为基于TADF的共掺杂系统的微观机制提供了更深入的理解，有助于在OLED的广泛领域中进一步发展有机磁场效应。
