Mechanochromism of Glassy Polymers Enabled by a Loop‐Forming Supramolecular Mechanophore

ABSTRACT Glassy polymers containing a supramolecular mechanophore capable of responding to mechanical deformation are reported. The supramolecular mechanophore LOOP, which comprises two perylene diimide (PDI) moieties that are connected by a flexible linker, was functionalized with an atom transfer radical polymerization initiator, allowing the direct growth of each glassy polymer poly(methyl methacrylate) (PMMA), polystyrene (PS), and poly(ethyl methacrylate) (PEMA), from the mechanophore. Under different mechanical deformation modes, including grinding, tensile stretching, and scratching, films of LOOP‐containing glassy polymers show a readily detectable fluorescent color change, on account of mechanophore activation. Fluorescence spectroscopy, confocal microscopy and fluorescence lifetime microscopy were used to quantify the mechanochromic responses, which allow direct monitoring and visualization of pre‐failure damage and local fracture events induced by tensile deformation or scratching. The results demonstrate that LOOP can serve as an optical reporter of mechanical deformation and support the broader suitability of intrinsically reversible supramolecular mechanophores for probing irreversible mechanical processes in polymeric materials, including glassy states where chain mobility is strongly restricted.