Thermally Induced Intra-Carboxyl Proton Shuttle in a Molecular Rack-and-Pinion Cascade Achieving Macroscopic Crystal Deformation.
Huang YG1,2, Shiota Y1, Su SQ1, Wu SQ1, Yao ZS1, Li GL1, Kanegawa S1, Kang S1, Kamachi T1, Yoshizawa K1, Ariga K2, Sato O1.
Angew Chem Int Ed Engl. 2016 Nov 14;55(47):14628-14632. doi: 10.1002/anie.201607886. Epub 2016 Oct 13.
Proton transport via dynamic molecules is ubiquitous in chemistry and biology. However, its use as a switching mechanism for properties in functional molecular assemblies is far less common. In this study, we demonstrate how an intra-carboxyl proton shuttle can be generated in a molecular assembly akin to a rack-and-pinion cascade via a thermally induced single-crystal-to-single-crystal phase transition. In a triply interpenetrated supramolecular organic framework (SOF), a 4,4'-azopyridine (azpy) molecule connects to two biphenyl-3,3',5,5'-tetracarboxylic acid (H4 BPTC) molecules to form a functional molecular system with switchable mechanical properties. A temperature change reversibly triggers a molecular movement akin to a rack-and-pinion cascade, which mainly involves 1) an intra-carboxyl proton shuttle coupled with tilting of the azo molecules and azo pedal motion and 2) H4 BPTC translation. Moreover, both the molecular motions are collective, and being propagated across the entire framework, leading to a macroscopic crystal expansion and contraction.© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
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