Surface-Governed Photoredox Reactivity of CsPbBr ₃ Quantum Dots

Surface chemistry is central to the design of colloidal quantum dots (QDs) for photoredox catalysis, where charge transfer, access to active sites, and colloidal stability must be balanced. Using CsPbBr₃ QDs as a model system, we show that systematic variation of surface ligand coverage serves as a diagnostic tool to distinguish reactions proceeding via direct electron transfer through the ligand shell from those dependent on chemisorption. In the latter case, reducing surface coverage increases the rates of reactions requiring substrate adsorption, such as C(sp³)-H brominations, with yields measured at a constant time increasing by up to 3-fold without compromising QD stability. This improvement arises from the efficient activation of chemisorbed substrates, which scales with the number of available surface sites. Extending this approach, we demonstrate that substrate adsorption on CsPbBr₃ QDs enables the activation of more demanding chlorinated compounds, establishing surface coverage as a key parameter for controlling reactivity in QD-based photocatalysis.