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Updated: Jun 28, 2026

Constructing Thioether/Vinyl Sulfide-tethered Helical Peptides Via Photo-induced Thiol-ene/yne Hydrothiolation
Published on: August 1, 2018
Direct Evidence for the Sulfonium-Mediated Photopolymerization of 1,2-Dithiolanes
Benjamin R Nelson1,2, Emeline C Lochmaier3, Bruce E Kirkpatrick1,2,4
1Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, Colorado 80303, United States.
None:
Light-induced, initiatorless homopolymerization of 1,2-dithiolanes is widely attributed to radical propagation. However, several experimental observations, including copolymerization behavior and EPR measurements, are inconsistent with this assignment. Here, this reaction is examined using in situ photoNMR, revealing first-order monomer consumption that is incompatible with a propagating radical mechanism. PhotoNMR further enables direct observation of a sulfonium intermediate attributed to a charge-transfer complex, corroborated through steady-state and transient absorption spectroscopy. Together, these data establish an activated-monomer-type polymerization, proceeding through a cationic rather than radical pathway. This same intermediate also enables controlled chain growth and is leveraged as a photoinitiator for cationic vinyl ether polymerization, extending the scope of dithiolane photochemistry beyond homopolymer formation and opening new opportunities for dithiolane-based photopolymerization strategies.
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