Mechanofluorochromic Elastomers Based on Reversible Helical Transition of Poly(phenylacetylene)s

Abstract Mechanofluorochromic (MFC) materials possessing both high sensitivity and excellent reversibility are crucial for achieving real‐time mechanical sensing and biomedical probing. Nonetheless, it currently faces the challenge of possessing both critical properties at excellent levels. Herein, we have proposed a reversible polymer mechanochromic mechanophore utilizing a novel mechanism that enables “turn‐off” fluorescence, triggered by a force‐induced helical conformational transition in poly(phenylacetylene) (PPA) from the fluorescent compact cis‐cisoid ( cc ) to the non‐fluorescent loose cis‐transoid ( ct ) conformation. Upon release, the restoring force, coupled with the reformation of intramolecular hydrogen bonds, drives the helical backbone to revert to cc conformation, thus enabling reversible mechanofluorochromism. A series of helical PPAs featuring vinyl groups underwent covalent crosslinking with polydimethylsiloxane (PDMS), yielding a range of MFC elastomers. We developed an in situ stretching‐fluorescence testing device to achieve real‐time monitoring of force‐dependent photoluminescence (PL) spectra. By adjusting the crosslinking density, Vi‐CP‐0.01@PDMS‐0.003 exhibited the highest MFC sensitivity. Significantly, the novel MFC elastomer showcases outstanding reversibility, maintaining its performance across 10 cycles. This study demonstrates a novel MFC mechanism that produces elastomers with high sensitivity and excellent reversibility, paving the way for further MFC materials development based on innovative mechanism.