The development of materials that exhibit a color change in response to mechanical force mimics biological mechano-transduction pathways that translate mechanical stimuli into chemical signals and elicit a change of the materials’ properties. One motivation for the development of such materials is to develop approaches that allow the detection of mechanical damage in polymeric materials. Several chemical motifs, referred as “mechanophores”, have been developed to respond to mechanical activation through the scission of covalent bonds. Alternatively, non-covalent interactions, which offer dynamic behavior, tunable interaction strength, and reversibility, can be exploited to achieve mechanochromic behavior. Here, we present several recent mechanochromic materials systems based on this general mechanism. For example, blends of telechelic molecules terminated with excimer-forming dyes enable mechanochromic fluorescent responses when blended into a broad variety of polymers. A new thiosemicarbazide-naphthalimide-based chromophore forming ionic complexes via a proton transfer was exploited as non-covalent mechanophore to induce colorimetric response. Here, the binding event causes a substantial red shift of the absorption, resulting in a color change from yellow to purple. The protonated complex can be mechanically dissociated in the solid state. Finally, microcapsules filled with solutions of aggregachromic chromophores were exploited to access mechanochromic materials. The capsules were incorporated into various polymers and release their cargo upon being damaged through mechanical impact. The physical changes which the dye molecules experience in this process lead to a visual color change in the damaged region of the material. We demonstrate that several physical effects can be exploited to achieve such behavior and show that the self-calibrating feature of such systems allows for quantitative assessment of the structural integrity.

Approaches towards the design of mechanochromic materials relying on supramolecular interactions

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.