  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.
