Issue 41, 2023

Thiophene-fused boron dipyrromethenes as energy efficient near-infrared photocatalysts for radical polymerizations

Abstract

Rapid near-infrared (NIR) light driven polymerizations have the potential to enable energy-efficient, benign, and multimaterial manufacturing for applications ranging from tissue engineering to soft robotics. However, achieving photopolymerization rates with NIR light that are viable for emergent additive manufacturing technologies (∼0.1–1.0 M s−1 at light intensities <40 mW cm−2) has proven challenging due to its inherently low energy. Herein, we begin to take down these barriers through a systematic investigation of four distinct thiophene-fused boron dipyrromethene (BODIPY) photocatalysts. Through extended π-conjugation, the thiophene-fused BODIPYs effectively absorb NIR (>780 nm) light and drive efficient acrylate polymerizations upon exposure to low-intensity (2.5–40 mW cm−2) NIR light emitting diodes (LEDs). The installation of bromine atoms is shown to further improve NIR light-fueled photopolymerization efficiency by a factor of ∼1.5×. This enhancement was rationalized by the formation of long-lived spin-triplet excited states via intersystem crossing, as observed using ultrafast transient absorption spectroscopy. However, the triplet yields are modest (∼6–14%), suggesting efficient charge transfer from singlet excited states also occurs within the present photosystem. Finally, optimization of resin formulations containing non-halogenated thiophene-fused BODIPY photocatalysts is shown to provide unprecedented polymerization rates (0.33 M s−1) upon exposure to an 850 nm LED at an intensity of 20 mW cm−2. The structure–reactivity relationships identified herein provide key insights that will inform further design and optimization of energy-efficient, NIR light-driven polymerizations with utility in photocurables for coatings, adhesives, and 3D printing.

Graphical abstract: Thiophene-fused boron dipyrromethenes as energy efficient near-infrared photocatalysts for radical polymerizations

Supplementary files

Article information

Article type
Paper
Submitted
27 Jul 2023
Accepted
07 Sep 2023
First published
13 Sep 2023
This article is Open Access
Creative Commons BY-NC license

J. Mater. Chem. A, 2023,11, 22259-22266

Thiophene-fused boron dipyrromethenes as energy efficient near-infrared photocatalysts for radical polymerizations

A. Stafford, S. R. Allen, T. A. Grusenmeyer, C. J. O'Dea, L. Estergreen, S. T. Roberts and Z. A. Page, J. Mater. Chem. A, 2023, 11, 22259 DOI: 10.1039/D3TA04462A

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