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

Area of Science:

• Photochemistry and Materials Science
• Chemical Biology

Background:

• Photocages offer spatiotemporal control via light-induced payload release, typically through heterolytic processes.
• Unintended radical generation via homolytic pathways can cause off-target effects in photocage applications.
• Controlled radical photorelease remains underexplored due to unknown governing molecular factors.

Purpose of the Study:

• To investigate the influence of photophysics and payload identity on heterolytic versus homolytic reactivity in BODIPY photocages.
• To establish a structure-reactivity framework for predictable light-controlled radical generation.

Main Methods:

• Investigated BODIPY photocages with varying substituents to analyze photophysical properties and photorelease pathways.
• Quantified radical photorelease quantum yields and compared them with heterolytic uncaging.
• Demonstrated Type I photoinitiation of RAFT polymerization using the developed radical photorelease system.

Main Results:

• High fluorescence quantum yields in BODIPY photocages correlate with efficient homolytic cleavage, enabling reversible radical catch-and-release.
• Introduction of iodide or boron-methyl substituents suppresses radical release by promoting intersystem crossing.
• Achieved a record 0.5% photorelease quantum yield for green-light-driven radical generation, exceeding heterolytic carboxylate uncaging.

Conclusions:

• Established a structure-reactivity framework for predictable light-controlled radical generation from photocages.
• Demonstrated suppression of unwanted radical effects and enabled controlled radical photorelease.
• Opened new avenues for late-stage photochemical payload installation and radical-based applications like polymerization.