吡咯并吡咯二酮/异靛蓝为受体的红光热致延迟荧光材料构筑及辐射衰减调控

Thermally activated delayed fluorescence (TADF) recently has become a viable alternative for harvesting both singlet and triplet state in OLEDs via effective reverse intersystem crossing (RISC) mechanism. However, several challenged issues must be addressed such as 1) difficulty to simultaneously achieves effective RISC and highly efficient fluorescent radiation, 2) deficiency of red or near-infrared TADF materials and 3) the notorious electroluminescence efficiency roll-off in increasing brightness. This project addresses these important technology challenge through developing D-π-A-π-D-type red and near-infrared TADF materials using diketopyrrolopyrrole or isoindigo as acceptor building blocks and phenyl, styrly or phenyethynyl fragment as bridge unit. The steric effect between the acceptor and bridge unit is considered to enhance the electron delocalized distribution of HOMO and LUMO in bridge unit, resulting in enhanced singlet radiation efficiency. The spatial separated distance between the acceptor and donor is used to control singlet-triplet splitting energy, resulting in improved RISC. Furthermore, the Ag nanostructures would be developed and their effects on excited state dynamics of TADF materials would be investigated. Finally, these Ag nanostructure would be incorporated into OLEDs to suppress the notorious electroluminescence efficiency roll-off by modifying the radiative decay rate of singlet, which would improve reverse intersystem crossing from triplet to singlet, decreasing the triplet concentrations. Under this grant, this project would develop a new donor-acceptor TADF material system and some rules directing future molecular design. In addition, the detailed interaction mechanism between the TADF materials and surface Plasmon resonances of the Ag nanostructures would be elucidated.

热致延迟荧光通过三线态（T1）到单线态（S1）的反向系间转化（RISC）发光，为暗态T1激子低成本发光利用提供了有效途径，但有几个关键问题亟待解决: 增强RISC过程与伴随的S1辐射效率下降; 缺乏高效的红光TADF材料; 高亮度下器件效率滚降严重。本项目拟构筑吡咯并吡咯二酮和异靛蓝为受体，苯环、苯乙烯或苯乙炔基为桥连骨架的D-π-A-π-D型红光材料，通过调控与受体相连骨架的位阻强化LUMO与HOMO在桥连骨架电子云分布，增强辐射效率；调控给-受体空间分离距离控制S1与T1分裂能,，促进RISC过程。构筑Ag纳米微结构，研究其对材料激发态光动力行为的影响，然后集成到OLED器件，利用等离子共振激元加快S1辐射，破坏T1与S1平衡，促进RISC过程，降低T1浓度。项目研究将会建立新的给-受体材料体系和分子设计原则， 阐明采用分子设计和金属纳米结构对材料激发态光动力行为调控的机制。

热活化延迟荧光（TADF）材料被誉为第三代有机电致发光材料，是当前有机电致发光材料研究领域的热点。项目研究围绕高效率TADF材料新体系的开发，发展了新的呋喃[2,3-B]喹喔啉发光分子骨架，研究了含呋喃[2,3-B]喹喔啉核心骨架不同数量稠环材料的发光性能，电荷传输性能，发现了发光性能与商用蒽类、芘类、含硼类材料相当的新蓝色荧光染料体系，有望实现进口商用蓝光材料的替代；设计合成了含呋喃[2,3-B]喹喔啉核心骨架为受体单元构筑的D-A和A-π-A线性结构材料，获得了10.88%（3.4 cd m-2）的最大外量子效率和1000 cd /m2亮度时外量子效率仍然接近8%的新型荧光材料，新发展的染料采用非掺杂器件实现了高达47813 cd m-2的亮度，3.8%（104 cd m-2）的最大外量子效率，在极高亮度10000，20000和30000 cd m-2时，外量子效率分别为3.2%，3.1%和3.0%，滚降率低于3.1%。项目围绕D-A型TADF分子设计增强RISC过程时导致S1态激子辐射效率下降之间的矛盾，提出了以呋喃[2,3-B]喹喔啉骨架为受体，苯胺类单元为给体，苯的邻位连接给、受体单元构建折叠型结构TADF材料的分子设计思路。围绕TADF为发光染料器件存在的高亮度下效率滚降问题，研究提出了TADF敏化荧光发光机制中，利用异质结产生延迟荧光，将荧光染料掺杂到远离异质结界面，实现荧光染料掺杂区域与三线态激子产生区域分离的器件设计思想。采用TCTA与PO-T2T界面形成的激基复合物为敏化剂，Rubrene为发光染料，实现了Rubrene器件外量子效率达到 8.0% (27 cd/m2)，电流效率达到24 cd/A(150 cd/m2)。