Ratiometric Mechano-Fluorescent Elastomers Dually Promoted via Effective Force-Triggered Radicals and Preeminent Toughnesses/Stretchabilities by Unconventional Shuttling Dimensions of Tetraphenylethylene-Suspended [c2] Daisy Chain Rotaxanes

TL;DR

Scientists created a new type of stretchy material that changes color when stretched, using special molecular structures to make it tough and responsive.

Contribution

The paper introduces a novel method of enhancing polymer toughness and stretchability using daisy chain rotaxanes with unconventional shuttling dimensions.

Findings

PU films with daisy chain structures showed a record toughness of 1363 MJ/m³, 6.3 times tougher than standard PU films.

The material exhibited ratiometric fluorescent responses under stretching, enabling reversible dual fluorescent switching.

Thermal treatments enabled shape memory and reversible fluorescence behaviors in the material.

Abstract

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.

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