Light-driven radical catch-and-release with BODIPY photocages

Photocages release payloads upon light irradiation and are widely used for spatiotemporal control in chemical biology and materials science. Although payload release is almost universally described as a heterolytic process, homolytic pathways that generate radicals can interfere and produce unintended off-target effects. If controlled, radical photorelease would open new avenues for applications such as polymerization, however the molecular factors that govern this process in photocages remain unknown. Here, we investigate how photophysics and payload identity influence heterolytic vs. homolytic reactivity in BODIPY photocages. We find that high fluorescence quantum yields correlate with efficient homolytic cleavage, enabling reversible radical catch-and-release: light-assisted capture of radical payloads followed by clean photorelease under green light illumination. This radical release can be suppressed by the introduction of iodide or boron-methyl substituents which promote intersystem crossing. We achieve the highest photorelease quantum yield reported to date for green-light-driven radical generation (Φr = 0.5%), surpassing heterolytic carboxylate uncaging. We further exploit this reactivity in Type I photoinitiation of RAFT polymerization, yielding fluorescently labelled polymers with defined dispersity. This work establishes a structure–reactivity framework for predictable light-controlled radical generation, enabling mitigation of off-target radical effects and opening new avenues for late-stage photochemical payload installation.