Wang Lu, Ou Qi, Peng Qian, Shuai Zhigang
MOE Key Laboratory of Organic OptoElectronics and Molecular Engineering, Department of Chemistry, Tsinghua University, Beijing 100084, People's Republic of China.
School of Chemical Sciences, University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China.
J Phys Chem A. 2021 Feb 25;125(7):1468-1475. doi: 10.1021/acs.jpca.0c09767. Epub 2021 Feb 15.
The thermally activated delayed fluorescence (TADF) phenomenon has attracted increasing attention because it can harvest 100% of the electro-pumped carriers to form singlet bound excited state for fluorescence. It is generally believed that the small energy gap between S and T (Δ) is essential for TADF to facilitate the reverse intersystem crossing (rISC). However, for a few donor-acceptor (D-A) organic compounds with small Δ, the TADF phenomenon is absent, indicating that Δ might not be a good molecular descriptor. Here, using our self-developed thermal vibration correlation function (TVCF) formalism in combination with quantum chemistry calculations, we revisit the key factors that dominate the TADF property for 11 D-A systems with small Δ. Based on our theoretical results in comparison to experiments, we conclude that the activation energy Δ is a good molecular descriptor to characterize the TADF performance because a significantly better linear relationship is observed between Δ and the rISC rate constant () compared to that between Δ and . These findings provide deeper understanding of the TADF mechanism, shedding light on the molecular design of high-performance TADF materials.
热激活延迟荧光（TADF）现象因其能使100%的电泵浦载流子形成单重态束缚激发态以产生荧光而受到越来越多的关注。人们普遍认为，单重态（S）与三重态（T）之间的小能隙（Δ）对于TADF促进反向系间窜越（rISC）至关重要。然而，对于一些具有小Δ的供体-受体（D-A）有机化合物，TADF现象并不存在，这表明Δ可能不是一个好的分子描述符。在此，我们结合量子化学计算，使用自行开发的热振动相关函数（TVCF）形式体系，重新审视了11个具有小Δ的D-A体系中主导TADF性质的关键因素。基于我们与实验结果相比较的理论结果，我们得出结论，活化能Δ是表征TADF性能的一个良好分子描述符，因为与Δ和rISC速率常数（）之间的关系相比，Δ与之间观察到明显更好的线性关系。这些发现为TADF机制提供了更深入的理解，为高性能TADF材料的分子设计提供了启示。
