Although we have only considered a single molecule coupled to the cavity, the proposed modification of PMET rate can also be accomplished in the collective coupling regime (which involves many molecules coupled to the cavity as described in Sec. 6.2), involving both a modification of the effective driving force ∆G c 324,325 as well as the polaron decoupling mechanism. While having different chemical mechanisms, singlet fission reactions share much in common with charge transfer reactions in terms of how they can be controlled using light-matter coupling. 326 Like charge transfer reactions, singlet fission reactions are often modeled quantum mechanically with singlet and triplet surfaces that are shifted parabolas with certain driving forces and reorganization energies. These fission reactions can thus be controlled through light-matter coupling with the same effects previously described in this section. In particular, theoretical investigations have shown that cavities may increase or decrease triplet yield and production rate depending on the singlet fission parameters as well as cavity parameters such as the cavity frequency and coupling strength. The similar cavity control of singlet fission reactions and charge transfer reactions highlights the broad applicability of cavity modifications to many different types of photochemical reactions.