Aix-Marseille Univ., CNRS, ICR , 13397 Marseille , France.
J Chem Theory Comput. 2019 Mar 12;15(3):1503-1513. doi: 10.1021/acs.jctc.8b00923. Epub 2019 Feb 21.
Spin-exchange internal conversion (SEIC) is a general class of reactions having singlet fission and triplet fusion as particular cases. Based on a charge transfer (CT) mediated mechanism and analytical derivation with a model Hamiltonian, we propose proxies for estimating the coupling strength in both diabatic and adiabatic pictures for general SEIC reactions. In the diabatic picture, we demonstrated the existence of a bilinear relationship between the coupling strength and molecular orbital overlap, which provides a practical way to predict diabatic couplings. In the adiabatic picture, we showed that nonadiabatic couplings can be approximated by simple functions of the wave function CT coefficients. These approaches were verified through the investigation of singlet oxygen photosensitization, where both Δ and Σ oxygen states can be competitively generated by a triplet fusion reaction. The interplay between the CT-mediated mechanism, the spatial factors of the bimolecular complex, and the electronic structure of the oxygen molecule during the reaction explains the curiously small coupling to the Σ state along specific incidence directions. The results from both the diabatic and adiabatic pictures provide a comprehensive understanding of the reaction mechanism, which applies to general SEIC problems.
自旋交换内转换（SEIC）是一类普遍的反应，其中包括单态裂变和三重态融合作为特例。基于电荷转移（CT）介导的机制和模型哈密顿量的分析推导，我们提出了用于估计一般 SEIC 反应在非绝热和绝热图像中耦合强度的代理。在非绝热图像中，我们证明了耦合强度与分子轨道重叠之间存在双线性关系，这为预测非绝热耦合提供了一种实用方法。在绝热图像中，我们表明非绝热耦合可以通过波函数 CT 系数的简单函数来近似。这些方法通过 singlet oxygen photosensitization 的研究得到了验证，其中 Δ 和 Σ 氧态可以通过三重态融合反应竞争产生。在反应过程中，CT 介导的机制、双分子复合物的空间因素和氧分子的电子结构之间的相互作用解释了沿着特定入射方向与 Σ 态的耦合非常小的原因。非绝热和绝热图像的结果提供了对反应机制的全面理解，适用于一般 SEIC 问题。
