Yang Chou-Hsun, Hsu Chao-Ping
Institute of Chemistry, Academia Sinica, 128 Section 2 Academia Road, Nankang, Taipei 115, Taiwan.
J Phys Chem Lett. 2015 May 21;6(10):1925-9. doi: 10.1021/acs.jpclett.5b00437. Epub 2015 May 8.
The electronic coupling for singlet fission, an important parameter for determining the rate, has been found to be too small unless charge-transfer (CT) components were introduced in the diabatic states, mostly through perturbation or a model Hamiltonian. In the present work, the fragment spin difference (FSD) scheme was generalized to calculate the singlet fission coupling. The largest coupling strength obtained was 14.8 meV for two pentacenes in a crystal structure, or 33.7 meV for a transition-state structure, which yielded a singlet fission lifetime of 239 or 37 fs, generally consistent with experimental results (80 fs). Test results with other polyacene molecules are similar. We found that the charge on one fragment in the S1 diabatic state correlates well with FSD coupling, indicating the importance of the CT component. The FSD approach is a useful first-principle method for singlet fission coupling, without the need to include the CT component explicitly.
单线态裂变的电子耦合是决定速率的一个重要参数，现已发现，除非在非绝热态中引入电荷转移（CT）成分，主要是通过微扰或模型哈密顿量，否则该耦合太小。在本工作中，片段自旋差（FSD）方案被推广用于计算单线态裂变耦合。对于晶体结构中的两个并五苯，获得的最大耦合强度为14.8毫电子伏，对于过渡态结构则为33.7毫电子伏，这产生了239或37飞秒的单线态裂变寿命，总体上与实验结果（80飞秒）一致。对其他多并苯分子的测试结果类似。我们发现，在S1非绝热态中一个片段上的电荷与FSD耦合有很好的相关性，这表明CT成分的重要性。FSD方法是一种用于单线态裂变耦合的有用的第一性原理方法，无需明确包含CT成分。
