以“RISC为主，TTA为辅"的新机制高效利用三线态激子的深蓝光OLED材料的设计、合成及性能研究

The exploitation of high-performance deep-blue organic light-emitting diode (OLED) materials is the key to kick off the commercialization of OLEDs. Although electrofluorescent materials capable of harvesting triplet excitons (i.e., the “new-generation” OLED materials) are perspective candidates to fabricate high-performance low-cost OLEDs, so far most of the “new-generation” deep-blue OLEDs suffer from an unsatisfactory trade-off between efficiency and efficiency roll-off, which should be ascribed to their inherent triplet exciton harvesting mechanisms. In view of these problems, herein we propose a novel triplet exicton harvesting mechanism, i.e.,“reverse intersystem crossing (RISC) dominated, triplet-triplet annihilation (TTA) assisted” mixed mechanism, so that the “hot” and “cold” triplet excitons could be rapidly and efficiently harvested via RISC and TTA processes, respectively, leading to simultaneously enhanced triplet exciton utilization efficiency and reduced efficiency roll-off. Through in-depth analysis on the energy level alignment and molecular structure requirements of the corresponding materials, a variety of novel deep-blue OLED materials will be designed and synthesized, and high-performance deep-blue OLEDs showing not only high efficiency but also low efficiency roll-off will be fabricated. Furthermore, through in-depth studies on structure-properties correlations of these materials, the transformation and utilization processes of triplet excitons within OLEDs might be unveiled. The implementation of this project is expected to provide new ideas for the development of OLED materials, to provide new materials for the commercialization of OLEDs, and to gain new insight to the structure-properties correlations of OLED materials as well.

高性能的深蓝光有机电致发光(OLED)材料的开发是推进OLED产业化进程的关键。虽然“新一代”电致荧光材料有望能集高性能与低成本于一身，但受限于其各自对三线态激子的利用机制，现有的此类深蓝光OLED难于兼具高的效率和低的效率滚降。本项目针对目前深蓝光材料开发所存在的问题，提出“反系间窜越（RISC）为主，三线态-三线态湮灭（TTA）为辅”的三线态激子利用新机制，通过将“热”和“冷”的三线态激子分别经RISC和TTA途径予以高效转化、利用，从而提高器件效率，并降低器件的效率滚降。通过对能实现这一机制的材料的能级要求和分子结构的深入分析，设计、合成多种新型深蓝光OLED材料，制备兼具高效、低效率滚降的高性能深蓝光OLED，并深入研究分子的构效关系，探索OLED中三线态激子的转化、利用机制。本项目的实施有望为OLED材料的开发提供新思路，为OLED的产业化提供新材料，为分子的构效关系提供新认识。

在有机电致荧光器件（FOLED）中，如能以“反系间窜越（RISC）为主、三线态-三线态湮灭（TTA）为辅”的机制将三线态激子高效转化为单线态激子，则不但能实现高的激子利用率，还能在较大的电流密度范围内获得稳定的器件发光效率，从而解决FOLED领域中现存的“深蓝光和纯红光器件的性能不够理想”的关键科学问题。本项目以开发基于“RISC+TTA”机制的高性能FOLED材料为主要研究内容，不仅设计、合成出了多种能通过“RISC+TTA”的机制来利用三线态激子的新型高性能FOLED材料，而且还建立起了“RISC+TTA”型FOLED材料的理性结构设计策略，取得了如下重要研究结果：1）开发出了多种高性能的“RISC+TTA”型深蓝光FOLED材料，以其为发光材料所制得的深蓝光FOLED，可呈现出CIE1931色坐标为(0.152,0.065)、发光亮度为10480cd∙m-2、电流效率为11.1cd∙A-1、外量子效率为10.5%、激子利用率接近100%的优异电致发光性能；2）开发出了一种高性能的“RISC+TTA”型FOLED主体材料，基于其的纯红光FOLED，获得了CIE1931色坐标为(0.65,0.35)、发光亮度为12840cd∙m-2、最大激子利用率为63%、在0.1~550 mA∙cm-2的电流密度下能保持极为稳定的激子利用率（54%~63%）的高性能；3）建立起了“RISC+TTA”型FOLED材料的理性结构设计策略。另外，我们还开发出了首例紫外光热激活延迟荧光（TADF）材料，基于其的紫外光FOLED的外量子效率可高达9.3%，刷新了紫外光有机发光二极管的效率记录；首次建立了纯有机重水光学探针的理性设计策略。通过上述工作，不但探索出了一种新的三线态激子利用机制，建立起了“RISC+TTA”类FOLED材料的理性构建策略，还获得了多种高性能的新型有机光电功能材料。本项目的实施为高性能的FOLED材料的开发提供了新思路，为OLED及光学传感器等领域提供了新材料，为理解材料的分子结构与光电性能的内在联系提供了新认识。