A modular approach to mechanically gated photoswitching with color-tunable molecular force probes
Molecular force probes conveniently report on mechanical stress and/or strain in polymers through straightforward visual cues. Unlike conventional mechanochromic mechanophores, the mechanically gated photoswitching strategy decouples mechanochemical activation from the ultimate chromogenic response, enabling the mechanical history of a material to be recorded and read on-demand using light. Here we report a completely redesigned, highly modular mechanophore platform for mechanically gated photoswitching that offers a robust, accessible synthesis and late stage diversification through Pd-catalyzed cross-coupling reactions to precisely tune the photophysical properties of the masked diarylethene (DAE) photoswitch. Using solution-phase ultrasonication, the reactivity of a small library of functionally diverse mechanophores is demonstrated to be exceptionally selective, producing a chromogenic response under UV irradiation only after mechanochemical activation, revealing colored DAE isomers with absorption spectra that span the visible region of the electromagnetic spectrum. Notably, mechanically gated photoswitching is successfully translated to solid polymeric materials for the first time, demonstrating the potential of the masked diarylethene mechanophore for a variety of applications in force-responsive polymeric materials.
Additional Information© 2021 The Author(s). Published by the Royal Society of Chemistry. This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence. All publication charges for this article have been paid for by the Royal Society of Chemistry. Submitted 27 May 2021; Accepted 21 Jul 2021; First published 22 Jul 2021. Financial support from Caltech is gratefully acknowledged. We thank the Center for Catalysis and Chemical Synthesis of the Beckman Institute at Caltech for access to equipment. We also thank Dr Mona Shahgholi and Dr David VanderVelde for technical assistance, and Dr Xiaoran Hu for helpful discussions. Author contributions: M. J. R. conceptualized the project and provided guidance during all stages. R. W. B. and M. J. R. designed the research. R. W. B. performed the experiments. R. W. B. and M. J. R. analyzed the data and wrote the manuscript. There are no conflicts to declare.
Published - d1sc02890a.pdf
Supplemental Material - d1sc02890a1.pdf