Assemblies of molecular switches at surfaces are of great interest for applications in solar energy conversion, optoelectronic and optomechanical devices. Recent experimental studies have demonstrated that it is possible to optically probe photoactive molecules in well-defined nanoscale environments. The goal of this research project is to obtain a microscopic understanding of the electronic and geometric effects on the photochemistry of molecules in well-defined environments. First-principles simulations based on a quantum embedding model will be used to understand the photochemistry of prototypical photochemical reactions. These studies will provide a detailed understanding of the influence of the substrate electronic coupling, geometry constraints from the surrounding matrix and cooperative effects on the photochemical reaction of surface bound molecules. The proposed theoretical tools address several crosscutting challenges identified in recent Basic Energy Science reports by developing methods to describe spectroscopic properties of molecules near complicated interfaces. This work will lead to significant advances in our understanding of surface-bound photoactive molecules which could lead to the next generation of materials for solar energy conversion, optoelectronic and optomechanical devices