Switchable Mechanochromic Poly(methyl acrylate) Enabled by Dianthryl Disilane

Abstract

Mechanochromic polymers have potential in visualization of microscopic damages in materials, and the integration of non-invasive switching into mechanochromic polymers can enable rich on-demand functionality of polymer materials. In this work, we report the development of a mechanoresponsive fluorescent polymer with photogated properties, comprising poly(methyl acrylate) (PMA) and the photoswitchable mechanophore S₂A₂, which features two anthracene groups linked by a disilane spacer. The mechanochromic polymer PMA-S₂A₂ exhibits ratiometric fluorescence response upon mechanical deformation, which arises from the monomer and excimer emission ratio of anthracene controlled by the polymer strain. The mechanochromic property of the polymer can be switched off by irradiation with 365 nm UV light which induces [4 + 4] cycloaddition of the anthracene groups between and within the polymer chains. Importantly, the anthracene dimers can be reversibly dissociated in situ within the polymer film by irradiation with 254 nm UV, restoring the mechanochromic function. Furthermore, intermolecular photodimerization of anthracene increases the molecular weight and forms an entanglement network, significantly enhancing the material toughness. This reversible photocontrolled switch design offers a novel strategy for developing mechanochromic materials with modulated responses and mechanical properties.