Mechanical force is a universal stimuli in nature. For example, force stimulates growth of bones, triggers stem cell differentiations, and regulates enzyme activities. In chemistry, force-transducing functional groups, i.e., mechanophores, offers a means to utilize mechanical energy to trigger downstream functionalities, such as unusual chemical reactivity, color changing, and generation of reactive species. The advancement to tailor-make mechanophores for materials applications requires quantitative understanding of mechanical-to-chemical processes and mechanophore libraries that are synthetically facile to expand.<br/>Here, we present three classes of mechanophores that are promising candidates for developing mechano-responsive systems. The first example shows that the fusion of bistable photoswitches with donor-acceptor adduct gives rise to novel mechano-responsive chromophores. The new chromophores demonstrate reversible and controllable visualization of force. The second example pictures a new paradigm for regulating mechanophore activation. The use of an ultrafast radical clock, i.e., SH/S● pair, seizes the diradical intermediates during cyclobutane ring-opening with pathway selection dependent on the radical clock. Lastly, we report a polymerization strategy utilizing nature’s mechanophore, disulfide, while achieving high molar mass. The new method is amendable to versatile derivatization, chain-end functionalization, and on-demand remodeling.<br/>In the future, we envision that sequence-controlled polymer backbones in conjunction with multi-stimuli responsive mechanophores will open doors to materials that take a multitude of external input (including mechanical force) to drive new structures and functions.

Next-generation mechano-responsive polymers:  See the force, tame the force, and wield the force

2019 Fall National Meeting

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