School of Chemical Sciences , Indian Association for the Cultivation of Science , 2A & 2B Raja S. C. Mullick Road, Jadavpur , Kolkata 700032 , WB India.
J Chem Theory Comput. 2019 Sep 10;15(9):5014-5023. doi: 10.1021/acs.jctc.9b00419. Epub 2019 Aug 26.
Singlet fission (SF) produces two coupled triplet excitons from a high energy singlet excitation. The mechanism of SF in a variety of phenyl (-Ph) substituted pentacene is systematically studied through both and density functional theory calculations. Two classes of substitution to pentacene are considered, namely, symmetric configuration with four Ph groups (TPP) and an asymmetric configuration with two Ph groups (DPP). The positions of the singlet and triplet states are determined by calibrating the active space through state averaged complete active space self-consistent field (SA-CASSCF) calculations. The SF rates are computed based on restricted active space with single and double spin flip wave functions (RAS-SF and RAS-2SF), which are analyzed based on different intermolecular π-stacking patterns of TPP and DPP. The contribution of charge transfer (CT) state near the multiexciton (ME) state plays a significant role for SF efficiency. The role of excimer formation is supportive for ME generation [ , , 617], and hence it is critically studied. The ME generation in TPP is a slower process and occurs through an excimer-mediated path with a large coupling between the first singlet excited state and ME state. On the other hand, DPP exhibits a relatively faster SF rate through the formation of a ME state via low-lying CT state, especially the slip-stacked dimers. The present computation elegantly demonstrates the crucial role of functional group substitution in the structure of SF active molecules in determining the efficiency of fission dynamics.
单线态裂变（SF）将高能单线态激发转化为两个耦合的三重态激子。通过和密度泛函理论计算，系统地研究了各种苯基（-Ph）取代五并苯中的 SF 机制。考虑了两种取代五并苯的方法，即具有四个 Ph 基团的对称构型（TPP）和具有两个 Ph 基团的不对称构型（DPP）。通过状态平均完全活性空间自洽场（SA-CASSCF）计算校准活性空间来确定单重态和三重态的位置。基于受限活性空间的单重和双重自旋翻转波函数（RAS-SF 和 RAS-2SF）计算 SF 速率，并根据 TPP 和 DPP 不同的分子间π堆积模式进行分析。靠近多激子（ME）态的电荷转移（CT）态的贡献对 SF 效率起着重要作用。激子复合物形成的作用对 ME 的产生有支持作用[,, 617]，因此对其进行了批判性研究。TPP 中的 ME 生成是一个较慢的过程，通过激子复合物介导的路径发生，其中第一单线态激发态和 ME 态之间存在较大的耦合。另一方面，DPP 通过形成低能 CT 态的 ME 态，特别是滑动堆积的二聚体，表现出相对较快的 SF 速率。本计算巧妙地证明了功能基团取代在 SF 活性分子结构中在确定裂变动力学效率方面的关键作用。
