Integrated transient chromophores for efficient photo-induced radiofluorination.

Photoredox catalysis has emerged as a powerful tool in organic synthesis, enabling substrate activation via visible light in the presence of an external photocatalyst. However, reliance on bimolecular interactions between the photoexcited catalyst and substrate limits efficiency, a critical drawback for applications such as radiolabeling. To address this challenge, we report a molecular design strategy that bypasses this constraint by integrating a transient chromophore directly into the substrate. This approach eliminates diffusion-dependent activation, achieving highly efficient transformations through a self-correcting mechanism: reactive intermediates either engage nucleophilic addition or revert to the ground state via decay, minimizing side reactions. The transient chromophore additionally acts as a charged leaving group, enabling facile purification of the neutral labeled product. We demonstrate this strategy in radiofluorination reactions, achieving superior yields and simplicity compared with conventional photoredox methods. Its utility is highlighted by the synthesis of positron emission tomography (PET) tracers for oncology, neurology, and cardiology.