Photocatalysis uses (sun)light to create new molecules or to break down pollutants. It is key to building a sustainable future. We need to improve the efficiency, selectivity and du-rability of this process. Covalent Organic Frameworks (COFs) are a new family of crystalline, porous polymers, that can be prepared in many structures and compositions to tune them in principle to any given photocatalytic reaction. A thorough understanding of the dynamics of the “excited state” of the irradiated catalyst is a crucial but challenging frontier to develop novel photocatalysts. Insights from this examination at extremely small time and length scales (up to femtoseconds and nanometers) will enable us to create a set of robust design rules to create potent COF-based photocatalysts and to validate them in the degradation of pollutants in air and in synthesizing hydrogen peroxide from air and water.