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

Abstract

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.

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