突破自旋统计极限的有机分子电致荧光的理论研究

High exciton utilization efficiency is the key criterion for a novel OLED light-emitting material to greatly superior to the traditional ones. Recently, the materials based on the thermal active delayed fluorescence (TADF) or the hybrided local charge transfer (HLCT) are not limited by the spin statistics principles and their exciton utilization efficiencies can up to 100% and are expected to developed into a low-cost and high-performance new generation OLED materials. This has attracted a lot of attention from the academic circle. However, in principles, it is impossible to get the high exciton utilization and the high radiative rate at the same time for TADF materials. Besides, the HLCT luminescent mechanics is unclear at present. All the issues need to be more deeply explored. Therefore, in the project, we will chose TADF and HLCT-based materials, and firstly construct the energy level structures of the molecular high excited states, and quantitatively calculate the transition rates between the related electronic singlet/triplet states, and then reveal the excited-state decay paths. We will focus on sovling the following key scientific issues: the calculation of adiabatic electronic coupling matrix between excited states in the framework of TDDFT, and the internal conversion rate and the radiative decay rate between the triplet states. In the end, by systematically analysizing the relationship between structure and property. we expect to provid the theoretical basises for the rational design of the OLED materials with high excition utilization efficiency and high lumienscence efficiency.

提高激子的利用率一直是OLED发光材料创新和突破的关键。最近，反系间窜越的延迟荧光（TADF）材料和杂化局域-电荷转移（HLCT）激子材料均突破了自旋统计极限，使得电致发光的激子利用率几乎达到100%，有望成为新一代低成本高性能的OLED材料，引起了广泛关注。然而，TADF材料中，存在激子的高利用率与高辐射速率之间是自相矛盾的问题，HLCT材料发光机制不明确的问题，亟待深入研究。本项目将针对TADF和HLCT分子材料，建造分子激发态能级结构，定量计算分析各电子态之间的相互转化速率及竞争关系，揭示激发态演变途径及规律。重点解决TDDFT框架下激发态之间的非绝热耦合计算、三线态之间内转换和辐射跃迁速率计算等关键问题。通过系统分析结构性能关系，为理性设计出高激子利用率和高发光效率的OLED材料提供理论依据和思路。

低激子利用率一直制约着OLED的发展，因此开发新的纯有机发光材料突破激子利用率25%的极限，是人们梦寐以求的事情。最近，系间窜越和反系间窜越控制的延迟荧光（TADF）、杂化电荷局域-电荷转移（HLCT）及纯有机室温磷光（RTP）材料均突破此极限，使得电致发光的激子利用率几乎达到100%，有望成为新一代低成本高性能的OLED材料，引起了广泛关注。然而，TADF 材料中存在激子的高利用率与高辐射速率之间是自相矛盾的问题；HLCT 材料发光机制不明确的问题；纯有机室温磷光体系比较稀有，存在有长寿命和磷光效率很难兼得的国际难题。. 本项目针对以上问题发展了新方法，提出了新模型和分子设计原则，取得了创新性进展：1）在国际上，首次得到了考虑激子相互作用的无辐射跃迁理论；2）实现了TADF体系的瞬态和延迟荧光效率的定量预测，揭示固相中分子堆积对激发态动力学的调控机制，建立高的激子利用率和强发光的平衡点，实现了高效率的TADF材料的理论设计与合成。3）揭示了HLCT 体系在溶剂中的吸收-发射光谱不对称的起源；4）通过理论设计操控系间窜越过程的开和关，实现有机体系在瞬态荧光、延迟荧光与磷光之间的转换，实验合成出混合荧光/磷光白光、双磷光白光及高灵敏度的机械力刺激响应等有机材料等。. 项目实施以来，共发表论文15篇，包括J. Am. Chem. Soc. (1), Angew. Chem. Int. Ed. (1, 已接受)，Chem.(1)，Nat. Commun.(2), J. Phys. Chem. Lett. (1), Chem. Sci. (1), Chem. Mater. (1), Nanoscale (1)，Adv. Opt. Mater. (1)，J. Phys. Chem. C (2), J. Phys. Chem. A (1), Chem. Phys. Lett. (1) 和Acta Chimica Sinica (1)。1篇Adv. Mater. 在修改。撰写了2016-2017化学学科发展报告中的聚集诱导发光研究进展/AIE理论拓展；中国学科发展战略理论预计算化学中的第四篇/第7章“有机发光材料的理论与计算”；ACS出版的《Aggregation-Induced Emission: Materials and applications》中的第12章。