In this section, we will review works that have proposed possible ways to modify photoexcited electron transfer reactions in the collective regime. Typical photoexcited electron transfer reactions occur between an optically bright donor state to an optically dark acceptor. As expected, the bright donor states have a large transition dipole (from the ground state) while the dark acceptors have a negligible transition dipole. This asymmetry can be exploited in a cavity, as cavity radiation only couples to optically bright states (here the donor state), allowing us to tune such chemical reactivity. An optical cavity can modify photoexcited electron transfer through a wide range of mechanisms. To appreciate this, consider the polariton states |±⟩ at resonance given by