Institute of Theoretical Chemistry, University of Vienna, Währinger Straße 17, 1090, Vienna, Austria.
Vienna Research Platform on Accelerating Photoreaction Discovery, University of Vienna, Währinger Straße 17, 1090, Vienna, Austria.
Angew Chem Int Ed Engl. 2023 Apr 3;62(15):e202217620. doi: 10.1002/anie.202217620. Epub 2023 Feb 28.
The mechanism behind reverse intersystem crossing (rISC) in metal-based TADF emitters is still under debate. Thermal rISC necessitates small singlet/triplet energy gaps as realized in donor-acceptor systems with charge-transfer excited states. However, their associated spin-orbit couplings are too small to account for effective rISC. Here, we report the first nonadiabatic dynamics simulation of the rISC process in a carbene-copper(I)-carbazolyl TADF emitter. Efficient rISC on a picosecond time scale is demonstrated for an initial triplet minimum geometry that exhibits a perpendicular orientation of the ligands. The dynamics involves an intermediate higher-lying triplet state of metal-to-ligand charge transfer character ( MLCT), which enables large spin-orbit couplings with the lowest singlet charge transfer state. The mechanism is completed in the S state, where the complex can return to a co-planar coordination geometry that presents high fluorescence efficiency.
金属基 TADF 发射器中反向系间窜越（rISC）的机制仍存在争议。热 rISC 需要小的单重态/三重态能隙，如具有电荷转移激发态的给体-受体体系所实现的那样。然而，它们相关的自旋轨道耦合太小，无法解释有效的 rISC。在这里，我们报告了首例卡宾-铜（I）-咔唑基 TADF 发射器中 rISC 过程的非绝热动力学模拟。对于初始三重态最低几何形状，证明了在皮秒时间尺度上有效的 rISC，该形状表现出配体的垂直取向。动力学涉及具有金属-配体电荷转移特征（MLCT）的中间较高三重态，这使得与最低单重电荷转移态具有较大的自旋轨道耦合。该机制在 S 态中完成，其中复合物可以返回到呈现高荧光效率的共面配位几何形状。
