Ratiometric Mechano-Fluorescent Elastomers Dually Promoted via Effective Force-Triggered Radicals and Preeminent...

Innovative radical-type mechano-fluorescent polyurethane (PU) elastomers were developed by integrating axle- and macrocycle-exerted force modes of tetraphenylethylene (TPE)-functionalized daisy chain rotaxanes with expanded/contracted conformations into polymer matrices, revealing distinct mechanical and optical performances under external tensile forces. Surprisingly, the designed PU films containing negligible amounts (0.02% molar ratio of all monomers) of daisy chain structures with unconventional shuttling dimensions (as artificial molecular muscle tougheners) exhibited ultrastretchable capabilities and preeminent toughnesses, possessing a record-high toughness of 1363 MJ/m³ at the strain rate of 20 mm/s, approximately 6.3 times tougher than the standard PU films, along with a significant loading weight ratio of 150,000. Additionally, appealing ratiometric fluorescent responses between blue-emissive TPE stoppers and yellow-emissive diarylacetonitrile radical species could be detected in PU films by stretching due to the introduction of TPE-based daisy chain rotaxanes into mechano-fluorophoric PU skeletons, enabling reversible dual fluorescent switching during tensile loading and unloading processes. Remarkably, notable shape memory and reversible ratiometric fluorescence behaviors of synthetic daisy chain-grafted PU films could be accessible by thermal treatments, indicating probable applications of mechanically interlocked molecule-functionalized PU films with splendid mechanical and optical features for designing stimuli-responsive smart materials.