Issue 22, 2023

Mechanochemical reactivity of a multimodal 2H-bis-naphthopyran mechanophore

Abstract

Multimodal mechanophores that react under mechanical force to produce discrete product states with uniquely coupled absorption properties are interesting targets for the design of force-sensing polymers. Herein, we investigate the reactivity of a 2H-bis-naphthopyran mechanophore that generates thermally persistent mono-merocyanine and bis-merocyanine products upon mechanical activation in solution using ultrasonication, distinct from the thermally reversible products generated photochemically. We demonstrate that a force-mediated ester C(O)–O bond scission reaction following ring opening establishes an intramolecular hydrogen bond, locking one merocyanine subunit in the open form. Model compound studies suggest that this locked subunit confers remarkable thermal stability to bis-merocyanine isomers possessing a trans exocyclic alkene on the other subunit, implicating the formation of an unusual trans merocyanine isomer as the product of mechanochemical activation. Density functional theory calculations unexpectedly predict a thermally reversible retro-cyclization reaction of the bis-merocyanine species that could explain the mechanochemical generation of the unusual trans merocyanine isomer.

Graphical abstract: Mechanochemical reactivity of a multimodal 2H-bis-naphthopyran mechanophore

Supplementary files

Article information

Article type
Paper
Submitted
29 Mar 2023
Accepted
02 May 2023
First published
10 May 2023

Polym. Chem., 2023,14, 2717-2723

Author version available

Mechanochemical reactivity of a multimodal 2H-bis-naphthopyran mechanophore

S. K. Osler, M. E. McFadden, T. Zeng and M. J. Robb, Polym. Chem., 2023, 14, 2717 DOI: 10.1039/D3PY00344B

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