Journal
ACS APPLIED MATERIALS & INTERFACES
Volume 11, Issue 27, Pages 24571-24576Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsami.9b06302
Keywords
mechanophore; rotaxane; BODIPY; mechanoresponsive luminescence; supramolecular mechanophore
Funding
- Japan Science Technology Agency (JST), PRESTO [JPMJPR17P6]
- Tanaka Rubber Science and Technology Award
- JSPS Core-to-Core Program, A. Advanced Research Networks
- Adolphe Merkle Foundation
- Swiss National Science Foundation through the Swiss National Center of Competence in Research Bio-Inspired Materials
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A red light-emitting photoluminescent supramolecular mechanophore based on an interlocked molecular motif is presented. The rotaxane-based mechanophore contains a cyclic compound featuring a pi-extended 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) dye as a red emitter that was threaded onto a dumbbell-shaped molecule containing an electron-poor 1,4,5,8-naphthalenetetracarboxylic diimide quencher at its center. Through two aliphatic hydroxyl groups attached to the dumbbell and the cycle, the mechanophore was covalently embedded into the backbone of a thermoplastic polyurethane elastomer. The mechanophore is only weakly photoluminescent in solution, indicating that the BODIPY's emission is efficiently quenched. Solution-cast films of the rotaxane-containing polymer, by contrast, show an appreciable photoluminescence, which suggests that during film formation, some of the emitting cycles are trapped in positions away from the quencher. Interestingly, the emission intensity could be significantly reduced by swelling the films with an organic solvent and the emission increased again upon drying, suggesting that such solvent plasticization causes a reversible rearrangement. In both dry and solvent-swollen films, uniaxial deformation caused a significant, reversible increase of the emission intensity, on account of mechanically induced shuttling of the emitters away from and back to the quenchers. It is shown that the properties of the polymer can be tuned by the solvent, and that such plasticizing extends the small palette of approaches that allow modification of the activation stress of a given material system.
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