Singlet fission is a process in which one singlet exciton is converted to two triplets. Recent experimental study investigated how different crystal packing of perylenediimide (PDI) molecules modulates their singlet fission rates and yields. By employing a simple three-state kinetic model and restricted active-space configuration interaction method with double spin flip as well as ab-initio Frenkel-Davydov exciton model method, we study the electronic factors (excitation energies and coupling between relevant electronic states) responsible for the variation of singlet fission rates in these PDI derivatives. Our approach reproduces the trends in singlet fission rates and provides explanations for the experimental findings. The wave-function analysis of the adiabatic electronic states shows that in many model PDI structures the multi-exciton character is spread over several states, in contrast to previously studied systems. This different nature of the multi-exciton state poses interesting mechanistic questions. By mapping the relation between the stacking geometries of PDIs and the rates of the singlet multi-exciton formation and the binding energies, we suggest favorable PDI structures that should not lead to exciton trapping.

Singlet fission in perylenediimide dimers and crystals

2019 Spring National Meeting

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