J Am Chem Soc. 2020 Aug 26;142(34):14733-14742. doi: 10.1021/jacs.0c07136. Epub 2020 Aug 17.

Catalyst Halogenation Enables Rapid and Efficient Polymerizations with Visible to Far-Red Light.

Journal of the American Chemical Society

Alex Stafford, Dowon Ahn, Emily K Raulerson, Kun-You Chung, Kaihong Sun, Danielle M Cadena, Elena M Forrister, Shane R Yost, Sean T Roberts, Zachariah A Page

PMID: 32786788 DOI: 10.1021/jacs.0c07136

Abstract

The driving of rapid polymerizations with visible to near-infrared light will enable nascent technologies in the emerging fields of bio- and composite-printing. However, current photopolymerization strategies are limited by long reaction times, high light intensities, and/or large catalyst loadings. The improvement of efficiency remains elusive without a comprehensive, mechanistic evaluation of photocatalysis to better understand how composition relates to polymerization metrics. With this objective in mind, a series of methine- and aza-bridged boron dipyrromethene (BODIPY) derivatives were synthesized and systematically characterized to elucidate key structure-property relationships that facilitate efficient photopolymerization driven by visible to far-red light. For both BODIPY scaffolds, halogenation was shown as a general method to increase polymerization rate, quantitatively characterized using a custom real-time infrared spectroscopy setup. Furthermore, a combination of steady-state emission quenching experiments, electronic structure calculations, and ultrafast transient absorption revealed that efficient intersystem crossing to the lowest excited triplet state upon halogenation was a key mechanistic step to achieving rapid photopolymerization reactions. Unprecedented polymerization rates were achieved with extremely low light intensities (<1 mW/cm

Publication Types

• Journal Article
• Research Support, U.S. Gov't, Non-P.H.S.
• Research Support, Non-U.S. Gov't