Merocyanine-based photoacids as recyclable catalysts in visible-light-driven transformations

Visible light-driven proton transfer is crucial in nature and catalysis. Here, we report that protic merocyanine-based photoswitches act as efficient and recyclable homogeneous Brønsted acid catalysts under blue or green light irradiation. Photo-promoted proton release efficiently enables Friedel-Crafts reactions with easy catalyst recovery and reuse. Furthermore, by leveraging the high two-photon absorption cross-section of merocyanines, we successfully promote the reaction using near-IR light (λ ∼ 975 nm).