Mechanically Gated Formation of Donor–Acceptor Stenhouse Adducts Enabling Mechanochemical Multicolor Soft Lithography

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Mechanochromism is one of the most widely developed areas in the quickly emerging field of polymer mechanochemistry. Stress-sensitive molecules called mechanophores are designed to undergo productive chemical transformations in response to mechanical force including changes in color that are useful for sensing and patterning. A variety of mechanochromic mechanophores have been developed, but modulating the photophysical properties of the mechanically generated dyes generally requires the independent preparation of discrete derivatives. Here we introduce a mechanophore platform enabling mechanically gated multicolor 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 colored DASA photoswitch. Critically, the color and photochemical properties of the DASA are controlled by the identity of the amine and thus a single mechanophore can be differentiated post-activation to produce a wide range of functionally diverse DASA compounds. We highlight the unique reactivity of this system by establishing the concept of mechanochemical multicolor soft lithography whereby a complex multicolor composite image is printed into a mechanochemically active elastomer through an iterative process of localized compression and reaction with different amines. Our results demonstrate the first example of multicolor pattern reproduction from a single mechanophore, empowering the fabrication of complex stimuli-responsive materials and paving the way for applications in patterning, sensing, and encryption.