Fluorescent Imaging of Loop Mechanophore Unfolding in a Glassy Polymer

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A glassy polymer containing a supramolecular mechanophore capable of responding to mechanical deformation is reported. The supramolecular mechanophore LOOP, which comprises two perylene diimide (PDI) connected by a flexible linker, was functionalized with an atom transfer radical polymerization initiator, allowing direct growth of the glassy polymer poly(methyl methacrylate) (PMMA) from the mechanophore. Under different mechanical deformation modes, including grinding, tensile stretching, and scratching, films of LOOP-PMMA show a readily detectable fluorescent color change, as a result of mechanophore activation. Fluorescence spectroscopy and confocal microscopy were used to monitor the mechanochromic responses, which allow direct visualization of pre-failure damage and local fracture events induced by tensile deformation or scratching. By integrating a supramolecular mechanophore into a glassy polymer, we demonstrate superior sensitivity in detecting localized stress compared to covalent mechanophore systems, highlighting the potential of intrinsically reversible supramolecular mechanophores as optical reporters of irreversible mechanical events.

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