Not dark yet: strong light-matter coupling can accelerate singlet fission dynamics

Polaritons are unique hybrid light-matter states that offer an alternative way to manipulate chemical processes and change material properties. In this work we theoretically demonstrate that singlet fission dynamics can be accelerated under strong light-matter coupling. For superexchange-mediated singlet fission, state mixing speeds up the dynamics in cavities when the lower polariton is close in energy to the multiexcitonic triplet-pair state. We show that this effect is more pronounced in non-conventional singlet fission materials in which the energy gap between the bright singlet exciton and the multiexcitonic state is large (> 0.1 eV). In this case, the dynamics is dominated by the polaritonic modes and not by the bare-molecule-like dark states, and additionally, the resonant enhancement due to strong coupling is very robust even for energetically broad molecular states. The present results provide a new strategy to expand the range of suitable materials for efficient singlet fission by making use of strong light-matter coupling.