In this section, we will review theoretical works that propose the modification of photochemical reactivity in the collective regime. This is relevant for the present experimental setups where the individual lightmatter coupling remains vanishingly small but the collective Rabi-splitting is substantial due to the scaling by √ N with N as the number of molecules. Ref. 306 shows that when a mixture of photo-reactive molecules and photo-nonreactive molecules is strongly coupled to the same cavity mode, photoexcitation to the lower polariton can be used to enable reactions in the photo-reactive molecules. The main idea of this work follows from Kasha's rule for the molecule-cavity hybrid system which suggests that polaritonic excitations relax into the lowest energy state available to the cavity-molecule system. They use this to funnel energy, initially deposited to the lower polariton, to a molecule that can undergo a photochemical reaction to energy levels below the lower polariton. Through direct on-the-fly atomistic simulations, the author shows that collective strong coupling can be utilized to enable reactivity in a few photo-reactive molecules embedded in a large ensemble of non-reactive molecules.