Record release of tetramethylguanidine using a green light activated photocage for rapid synthesis of soft materials

Photocages have enabled spatiotemporally governed organic materials synthesis with applications ranging from tissue engineering to soft robotics. However, the reliance on high energy UV light to drive an often inefficient uncaging process limits their utility. These hurdles are particularly evident for more reactive cargo, such as strong organobases, despite their attractive potential to catalyze a range of chemical transformations. Herein, two metal-free boron dipyrromethene (BODIPY) photocages bearing tetramethylguanidine (TMG) cargo are shown to induce rapid and efficient polymerizations upon exposure to a low intensity green LED. A suite of spectroscopic characterization tools were employed to identify the underlying uncaging and polymerization mechanisms, while also determining reaction quantum efficiencies. The results are directly compared to state-of-the-art TMG-bearing ortho-nitrobenzyl and coumainylmethyl photocages, finding that the present BODIPY derivatives enable step-growth polymerizations that are >10x faster than the next best performing photocage. As a final demonstration, the inherent multifunctionality of the present BODIPY platform in releasing radicals from one half of the molecule and TMG from the other is leveraged to prepare polymers with starkly disparate physical properties. The present findings are anticipated to enable new applications of photocages in both small-molecule photochemistry for medicine and advanced manufacturing of next generation soft materials.

Automated summary

This study demonstrates the use of two metal-free boron dipyrromethene (BODIPY) photocages to induce rapid and efficient polymerizations upon exposure to low intensity green LED light. The uncaging and polymerization mechanisms were characterized using spectroscopic tools, and the reaction quantum efficiencies were determined. The BODIPY photocages showed significantly faster step-growth polymerizations compared to other TMG-bearing photocages. Additionally, the inherent multifunctionality of the BODIPY platform was leveraged to prepare polymers with distinct physical properties. These findings are expected to have important applications in small-molecule photochemistry and advanced manufacturing of soft materials.