Li Shuhang, Kuang Zhuoran, Li Yang, Wang Zeming, Wan Yan, Zhang Xian-Fu, Song Di, Xia Andong
State Key Laboratory of Information Photonic and Optical Communications, School of Science, Beijing University of Posts and Telecommunications (BUPT), Beijing 100876, P. R. China.
College of Chemistry, Beijing Normal University, Beijing 100875, P. R. China.
J Phys Chem B. 2024 Sep 26;128(38):9224-9232. doi: 10.1021/acs.jpcb.4c05498. Epub 2024 Sep 12.
In heavy-atom-free organic molecules, the rate of triplet generation through charge recombination, as dictated by the El-Sayed rule, can be enhanced by 10-10 times compared with the rate of spontaneous spin flipping between π-π* orbitals. This mechanism is known as the spin-orbit charge-transfer intersystem crossing (SOCT-ISC). Within the framework of the SOCT-ISC mechanism, facilitating the generation of charge-separated (CS) states and suppressing the spin-allowed direct charge recombination to the ground state are pivotal for maximizing the efficiency of generating localized triplet states. Herein, a series of orthogonal aryl-substituted boron-dipyrromethene dyads were studied by time-resolved spectroscopy to unravel the multichannel competitive relationships in the SOCT-ISC mechanism. The energy level of the electron donor and the stabilization of the solvent effect to the charge-transfer state are reflected in the Gibbs free energy changes of the electron transfer and recombination reactions, leading to significantly different triplet quantum yields. Additionally, solvation-induced electronic coupling changes in excited states lead to the fact that the spin-allowed charge recombination rate cannot be well simply predicted by the Marcus inverted region but has to consider the specific excited-state dynamics in optimizing the proportion of triplet generation channels based on charge recombination.
在无重原子的有机分子中，根据埃尔 - 赛义德规则，通过电荷复合产生三重态的速率，与π - π*轨道之间自发自旋翻转的速率相比，可以提高10到100倍。这种机制被称为自旋 - 轨道电荷转移系间窜越（SOCT - ISC）。在SOCT - ISC机制的框架内，促进电荷分离（CS）态的产生并抑制自旋允许的直接电荷复合到基态，对于最大化产生局域三重态的效率至关重要。在此，通过时间分辨光谱研究了一系列正交芳基取代的硼二吡咯亚甲基二元体系，以揭示SOCT - ISC机制中的多通道竞争关系。电子供体的能级以及溶剂效应对电荷转移态的稳定作用，反映在电子转移和复合反应的吉布斯自由能变化中，导致三重态量子产率有显著差异。此外，激发态中溶剂化诱导的电子耦合变化导致，自旋允许的电荷复合速率不能简单地通过马库斯反转区域很好地预测，而是在基于电荷复合优化三重态产生通道比例时必须考虑特定的激发态动力学。
