Institute of Chemistry , Academia Sinica , 128 Section 2 Academia Road , Nankang, Taipei 115 , Taiwan.
Institute of Chemistry , University of the Philippines Diliman , Quezon City 1101 , Philippines.
J Chem Theory Comput. 2019 Apr 9;15(4):2246-2253. doi: 10.1021/acs.jctc.8b01185. Epub 2019 Mar 21.
Intramolecular singlet fission and triplet-triplet annihilation (TTA) has been experimentally observed and reported. However, problems remain in theoretically accounting for the corresponding intramolecular electronic couplings and their rates. We used the fragment excitation difference (FED) scheme to calculate the coupling with states from restricted active-space spin-flip configuration interaction. We investigated three covalently linked pentacene dimers via a phenyl group in an ortho-, meta-, and para-arrangement. The singlet fission and TTA couplings were enhanced when two chromophores were covalently linked. With the Fermi golden rule, both the estimated singlet fission and TTA rates were in line with the experimental results. For systems with significant singlet-fission coupling, charge-transfer components were observed in the excited states involved, and charge-transfer states were also seen within 1 eV above the singlet excited states. Our approach allows for an analysis of through-bond versus through-space singlet fission in the full electronic wave functions. The FED scheme is useful for calculating intramolecular singlet-fission and TTA couplings.
分子内单重态裂变和三重态-三重态湮灭（TTA）已经被实验观察和报道。然而，在理论上解释相应的分子内电子耦合及其速率仍然存在问题。我们使用片段激发差（FED）方案来计算与受限活性空间自旋翻转组态相互作用的状态的耦合。我们通过苯基以邻位、间位和对位排列研究了三个共价连接的五苯二聚体。当两个发色团共价连接时，单重态裂变和 TTA 耦合得到增强。利用费米黄金定则，估计的单重态裂变和 TTA 速率都与实验结果一致。对于具有显著单重态裂变耦合的体系，在涉及的激发态中观察到了电荷转移成分，并且在单重激发态上方 1 eV 内也观察到了电荷转移态。我们的方法允许在全电子波函数中分析键间与键上的单重态裂变。FED 方案可用于计算分子内单重态裂变和 TTA 耦合。
