基于密度泛函理论的有机电致激光分子设计及筛选

Over the years, tremendous efforts have been devoted into the development of organic laser materials because of its easy and economic fabrication, wide coverage of the lasing wavelength, and the application in various fields such as spectroscopy probing and communication technology. While the optically pumped organic lasers have made promising progresses, lasing under electrical pumping remains one of the most challenging issues for organic luminescence materials. This is because: (1) three quarters of the excitons formed under electrical pumping are triplets, which is a long-live species and its accumulation will introduce re-absorption as well as the annihilation of the singlet exciton and even thermal degradation of the material; (2) the large amount of polarons will also result in re-absorption and the exciton annihilation; (3) electrodes will contribute to extra losses. Focusing on the optical gain material itself, we will carry out a systematic theoretical investigation on the electronic structural and photophysical properties of these organic materials based on density functional theory (DFT). Based on the calculation results over a wide range of systems, this work will propose general protocols for molecular design and screening of the electrical-pumped lasing candidates, which can eventually lead to the breakthrough of the electrically pumped organic lasers.

有机激光材料具有制备成本低廉、光谱覆盖波段广泛以及易于集成等优点，在光谱检测及通信领域等方面有着诱人的应用前景，多年来在有机光电领域备受关注。目前，光致有机激光材料的发展已取得了令人瞩目的成就，而在此基础上实现电致激光仍然是有机激光领域的瓶颈及难点。相比于光致激光，电致激光实现的条件更为苛刻，主要有如下几点原因：(1)电注入条件下形成的激子中75%为三线态，而三线态激子的累积会导致自吸收及单线态激子湮灭甚至激光材料的降解等问题；(2)电注入条件下会形成大量载流子，同样会带来自吸收及单线态激子湮灭的问题；(3)电极材料带来的极大损耗。聚焦于激光分子本身，本项目旨在通过密度泛函理论这一高效的理论方法对现有激光分子的电子结构及光物理过程进行系统性分析，通过针对大量有机发光体系的计算结果提出电致激光分子的筛选及设计理念，进而指导合成出高性能有机电致激光分子。

本项目针对有机激光这一有机发光领域的瓶颈问题，结合第一性原理计算和热振动关联函数速率理论，开展了多项致力于推动有机激光实验工作的理论研究。总结起来，本项目取得了如下几个方面的重要进展。首先，我们对具有强大电泵激光潜力的新型有机发光分子进行了研究，包括对于热活化延迟荧光(thermally activated delayed fluorescence, TADF)分子进行的系统而全面的理论分析，以及对一系列具有强发光和高传输性质的有机发光分子进行的发光机理探究。这将拓展有机激光增益介质的设计思路，为发光分子的设计/筛选奠定理论基础。接下来，我们基于沉淀下来的理论筛选流程，全面系统地分析了数十种TADF分子的电子结构及光物理性质，并根据净受激辐射截面筛选了具有电致激光潜力的TADF分子。此外，我们还探索了基于有机极化激元强化的逆系间窜越过程的机理，这将有效协助有机极化激元激光实验和理论工作的进一步开展。

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