Force-Dependent Multicolor Mechanochromism from a Single Mechanophore
We report a bis-naphthopyran mechanophore that exhibits force-dependent changes in visible absorption. A series of polymers incorporating a chain-centered bis-naphthopyran mechanophore was synthesized and mechanically activated using ultrasonication. By varying the length of the polymer chains, the force delivered to the mechanophore is modulated systematically. We demonstrate that the relative distribution of two distinctly colored merocyanine products is altered predictably with different magnitudes of applied force, resulting in gradient multicolor mechanochromism. The mechanochemical reactivity of bis-naphthopyran is supported by density functional theory calculations and described by a theoretical model that provides insight into the force–color relationship.
Additional Information© 2019 American Chemical Society. Received: May 16, 2019; Published: July 8, 2019. Financial support from Caltech and the Dow Next Generation Educator Fund is gratefully acknowledged. We thank Corey Husic, Anna Overholts, and Dr. Scott Virgil for helpful discussions and the Center for Catalysis and Chemical Synthesis of the Beckman Institute at Caltech for access to equipment. M.E.M. was supported by a NSF Graduate Research Fellowship (DGE-1745301). The authors declare no competing financial interest.
Supplemental Material - ja9b05280_si_001.pdf