Huang Zhongkai, Fujihashi Yuta, Zhao Yang
Division of Materials Science, Nanyang Technological University , Singapore 639798, Singapore.
J Phys Chem Lett. 2017 Jul 20;8(14):3306-3312. doi: 10.1021/acs.jpclett.7b01247. Epub 2017 Jul 7.
Intramolecular singlet fission (iSF) materials provide remarkable advantages in terms of tunable electronic structures, and quantum chemistry studies have indicated strong electronic coupling modulation by high frequency phonon modes. In this work, we formulate a microscopic model of iSF with simultaneous diagonal and off-diagonal coupling to high-frequency modes. A nonperturbative treatment, the Dirac-Frenkel time-dependent variational approach is adopted using the multiple Davydov trial states. It is shown that both diagonal and off-diagonal coupling can aid efficient singlet fission if excitonic coupling is weak, and fission is only facilitated by diagonal coupling if excitonic coupling is strong. In the presence of off-diagonal coupling, it is found that high frequency modes create additional fission channels for rapid iSF. Results presented here may help provide guiding principles for design of efficient singlet fission materials by directly tuning singlet-triplet interstate coupling.
分子内单重态裂变（iSF）材料在可调电子结构方面具有显著优势，量子化学研究表明高频声子模式能对电子耦合进行强力调制。在本工作中，我们构建了一个iSF的微观模型，该模型同时包含与高频模式的对角耦合和非对角耦合。我们采用了非微扰处理方法，即使用多个达维多夫试探态的含时变分狄拉克 - 弗伦克尔方法。结果表明，若激子耦合较弱，对角耦合和非对角耦合都有助于实现高效单重态裂变；而若激子耦合较强，则只有对角耦合能促进裂变。在存在非对角耦合的情况下，我们发现高频模式为快速iSF创造了额外的裂变通道。本文给出的结果可能有助于通过直接调控单重态 - 三重态态间耦合，为设计高效单重态裂变材料提供指导原则。
