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Catalyst Halogenation Enables Rapid and Efficient Polymerizations with Visible to Near-Infrared Light

preprint
submitted on 30.06.2020 and posted on 02.07.2020 by Alex Stafford, Dowon Ahn, Emily Raulerson, Kun-You Chung, Kaihong Sun, Danielle Cadena, Elena Forrister, Shane Yost, Sean Roberts, Zachariah Page
Driving rapid polymerizations with visible to near-infrared (NIR) 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. Improving 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 NIR 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/cm2) and catalyst loadings (< 50 μM), exemplified by reaction completion within 60 seconds of irradiation using green, red, and NIR light-emitting diodes.

Funding

Designing Wavelength-Specific Visible Light Photocurable Resins

United States Army

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Robert A. Welch Foundation (F-2007 to Z.A.P. and F-1885 to S.T.R.)

Research Corporation for Science Advancement, Cottrell Scholars Award (24489 to S.T.R.)

Center for Dynamics and Control of Materials

Directorate for Mathematical & Physical Sciences

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NNCI: Texas Nanofabrication Facility (TNF)

Directorate for Engineering

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History

Email Address of Submitting Author

zpage@utexas.edu

Institution

University of Texas at Austin

Country

United States

ORCID For Submitting Author

0000-0002-1013-5422

Declaration of Conflict of Interest

There are no conflicts to declare.

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