Stress-sensitive molecules called mechanophores undergo productive chemical transformations in response to mechanical force. A variety of mechanochromic mechanophores, which change colour in response to stress, have been developed, but modulating the properties of the dyes generally requires the independent preparation of discrete derivatives. Here we introduce a mechanophore platform enabling mechanically gated multicolour chromogenic reactivity. The mechanophore is based on an activated furan precursor to donor–acceptor Stenhouse adducts (DASAs) masked as a hetero-Diels–Alder adduct. Mechanochemical activation of the mechanophore unveils the DASA precursor, and subsequent reaction with a secondary amine generates an intensely coloured DASA. Critically, the properties of the DASA are controlled by the amine, and thus a single mechanophore can be differentiated post-activation to produce a wide range of functionally diverse DASAs. We highlight this system by establishing the concept of mechanochemical multicolour soft lithography whereby a complex multicolour composite image is printed into a mechanochemically active elastomer through an iterative process of localized compression followed by reaction with different amines.
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All data are available in the manuscript or the Supplementary Information. Experimental data and characterization data for all new compounds prepared in the course of these studies are provided in the Supplementary Information of this paper. The X-ray crystallographic coordinates for compound (±)-3 have been deposited at the Cambridge Crystallographic Data Center (CCDC) with deposition no. 2163133. These data can be obtained free of charge from the CCDC via www.ccdc.cam.ac.uk/structures/. Source data are provided with this paper.
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Financial support from Caltech is gratefully acknowledged. A.C.O. was supported by a National Science Foundation Graduate Research Fellowship (DGE-1745301) and an Institute Fellowship from Caltech. We thank M. Shahgholi for technical assistance with mass spectrometry and M. Takase for assistance with X-ray crystallography.
A.C.O. and M.J.R. are inventors on a US provisional patent application submitted by California Institute of Technology (CIT 8808-P) covering the chemistry and lithographic process disclosed herein.
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Supplementary Figs. 1–30, Tables 1 and 2, and Discussion.
Supplementary Data 1
Crystallographic data for compound (±)-3; CCDC reference no. 2163133.
Supplementary Data 2
The XYZ coordinates for the DFT calculations.
Source Data Fig. 1
Source data for CoGEF plot.
Source Data Fig. 3
Source data for UV–vis spectra.
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Overholts, A.C., Granados Razo, W. & Robb, M.J. Mechanically gated formation of donor–acceptor Stenhouse adducts enabling mechanochemical multicolour soft lithography. Nat. Chem. 15, 332–338 (2023). https://doi.org/10.1038/s41557-022-01126-5
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