有机半导体反向系间窜越体系的反常微观动力学及新奇磁效应

The third-generation organic light-emitting diodes with reverse intersystem crossing (RISC) characteristics are hotspots at present because of their low-cost high-efficiency luminescence. However, the complex and changeable microcosmic dynamics for RISC process is still controversial. To address this scientific issue, we have intentionally carried out four pre-research experiments for this project. The various organic magnetic field effects with different fingerprint responses are taken as the main research tools for detecting the related RISC mechanisms. Anomalous microcosmic dynamics and numerous novel magnetic field effects (including their trace shape and magnitude) were preliminarily observed from these four adopted systems with RISC molecules with exothermic process and as the energy transfer medium of three-body doping, as guest in two-body doping, and as energy well layer in quantum well structure. By adjusting the structural parameters and energy transfer process of the device, combining with steady and transient optical spectra, the rising and falling temperature experiments, and the utilization of the high magnetic field and other experimental methods, this project systematically explores the formation process, variety law, manipulation mechanism for organic magnetic effects in RISC systems, and clarifies the abnormal RISC phenomena and the physical origin of numerous novel magnetic field effects so as to fully reveal the micro-dynamic processes of RSIC. Therefore, this project can not only deepen the mechanism understanding of various delayed fluorescence from organic semiconductors, but also develop more efficient organic light-emitting devices with both RISC and TTA (triplet-triplet annihilation, i.e., triplet fusion) processes and have obvious scientific values and application prospects.

因在低成本就能成倍增强外量子效率，具有反向系间窜越（RISC）过程的第三代有机发光二极管是目前的热点，但其复杂多变的微观动力学机制还存在争议。针对这一科学问题，本项目专门进行了４种预研试验，采取有指纹示响应的有机磁效应作为RISC机制的主要研究对象，在放热过程的RISC体系和RISC分子分别作为三体掺杂的能量传递介质、二体掺杂的客体以及作为量子阱结构的势阱层等体系中初步观察到反常的微观动力学过程和许多新奇的磁效应现象。通过调控器件结构参数和能量传输方式，并结合稳态与瞬态光谱、升降温和施加强磁场等实验手段，系统探究RISC的形成过程、变换规律及其对有机磁效应的调控机制，阐明反常RISC过程和多种新奇磁效应的物理起源，以此全面揭示各类RISC的微观动力学过程。本项目既可加深有机半导体中多种延迟荧光机制的理解，还可开发兼具RISC和TTA过程的更高效率有机发光器件，具有明显的科学价值和应用前景。

该项目对有机半导体反向系间窜越体系(RISC)的反常微观动力学及新奇磁效应进行研究。存在反向系间窜越过程的有机半导体主要包括：激基复合物体系中分子间的电子-空穴对(electron-hole pairs包括EX1和EX3)、热活化延迟荧光(TADF)体系中分子内的电子-空穴对(包括CT1和CT3)以及传统有机荧光体系的极化子对(包括PP1和PP3)，这些研究体系及其RISC过程在增强发光器件的外量子效率(EQE)、降低效率滚降以及延长器件发光寿命方面具有重要科学价值和实际应用前景。项目取得以下主要研究成果：在激基复合物体系中观察到电流依赖的正常ISC到反常ISC的转换和反常RISC到正常RISC的转变，发现了TADF材料CzDBA掺杂器件的反常磁响应、电荷转移态激子发光磁效应的反常电流依赖关系以及激基缔合物器件中三重态-三重态湮灭的反常温度依赖关系，并对这些反常现象进行了较好解释；利用有机磁效应，在传统荧光材料DCJTB中观察到极化子对的反常RISC过程和它向ISC转变的现象，发现了传统高效发光体系红荧烯及其衍生物的高能三重态的RISC通道和得到了高达16.1%的外量子效率，并对Rubrene掺杂发光器件在低浓度下的反常电流依赖的RISC过程进行了较好解释。相关成果发表在Adv. Funct. Mater.、Adv. Mater. Interfaces、Mater. Hori.、ACS Photon.、Phys. Rev. Appl.、Appl. Phys. Lett.、J. Phys. Chem. Lett.、J. Mater. Chem. C等杂志上发表论文23篇；获准1项重庆市自然科学奖二等奖；申请国家发明专利1个。项目为理解第三代有机发光TADF和第一代有机荧光中激发态的物理微观机制和制备高效率、低效率滚降的长寿命发光器件奠定了坚实器件物理基础。