The development of mechanoresponsive materials is inspired by mechanosensory neurons or color changing chromatophores that can translate mechanical stimuli into a materials response. To artificially prepare such materials, non-covalent bonds are potentially useful mechanoresponsive moieties of tunable strength. In this context, we are exploiting supramolecular interactions to prepare materials which, upon mechanical activation, exhibit a macroscopic response such as a change of color.<br/>Here we explore the reversible coordination between amines and thiourea-carrying naphthalimide-based chromophores to prepare damage-sensing polymeric materials. In solution and in the solid state, primary, secondary, and tertiary amines coordinate to the thiourea-motif, inducing a substantial red-shift of the chromophore absorption and a color change from yellow to purple. Preliminary experiments demonstrate the responsive nature of these chromophore-amine complexes, as grinding of purple complex/polycaprolactone blends induced a color change to yellow that indicates complex dissociation. Bifunctional chromophores were subsequently blended with acrylic polymers carrying secondary amines and the material exhibited the purple color of the thiourea-amine complex with its absorption band at 530 nm. Upon tensile deformation, transmittance measurements showed that the intensity of the band of the complex decreased, while the signal for the non-coordinated chromophore at 390 nm increased in intensity. Moreover, the original spectra were recovered after release of the mechanical stress. Thus, the new material displays a reversible visual indication of mechanical deformation. In addition, these chromophores were embedded together with amine-containing microcapsules in different polymer matrices. Amine-chromophore complexes form upon rupture of the capsules, providing a facile pathway toward damage-reporting polymeric materials.

Towards mechanochromic materials based on non-covalent interactions

254th National Meeting (2017)

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