Rotaxane‐Based Mechanochromic Mechanophore Enabled by Amide Bond Formation

Mechanochromic mechanophores are molecular structures that alter their absorption and fluorescence properties in response to applied mechanical force. Supramolecular mechanophores, which operate without requiring covalent bond cleavage, respond to smaller forces with instantaneous and reversible fluorescence changes. Rotaxane-based supramolecular mechanophores offer exceptional design flexibility due to their molecular structures. However, previously reported rotaxane mechanophores have predominantly relied on azide-alkyne Huisgen cycloaddition for the final rotaxane formation, which restricts the incorporation of azide or alkyne functional groups within the resulting rotaxane structure. This study presents a novel approach for synthesizing rotaxane mechanophores by constructing the axle molecule through amide bond formation between a succinimidyl ester and an amino group. Polyurethane elastomer films containing the rotaxane mechanophore exhibited a rapid and reversible on/off switch in green fluorescence from 9,10-bis(phenylethynyl)anthracene upon cycle stretching. The new mechanophore demonstrated force-responsive behavior comparable to previously reported rotaxane mechanophores. The amide bond formation strategy enables the incorporation of diverse functional groups into rotaxane-based mechanophores, significantly broadening their potential applications.