Electronically Nonadiabatic Dynamics in Singlet Fission: A Quasi-Classical Trajectory Simulation

The recently developed symmetrical quasi-classical (SQC) method (Cotton, S. J.; Miller, W. H. J. Phys. Chem. A, 2013, 117, 7190) has been applied to a model system for molecular dimers of polyacenes, a family of organic materials for highly efficient solar energy conversion by using singlet fission (SF). Our results describe the electronic nuclear coupled dynamics of singlet fission very well for the model system, in good agreement with those recently obtained by using Redfield theory. The quantum interference between the charge transfer mediated pathway and the direct pathway of singlet fission has been investigated, and we found that pathway coherence may change the short-time SF dynamics quite a lot, even though the direct pathway itself may be very slow. The SQC method performs very efficiently in treating the model system with up to several thousand degrees of freedom and therefore shows a potential to be implemented to real complex molecular systems, such as singlet fission materials.