A multistate switchable [3]rotacatenane |
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Authors: | Barin Gokhan Coskun Ali Friedman Douglas C Olson Mark A Colvin Michael T Carmielli Raanan Dey Sanjeev K Bozdemir O Altan Wasielewski Michael R Stoddart J Fraser |
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Institution: | Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, USA. |
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Abstract: | Rotacatenanes are exotic molecular compounds that can be visualized as a unique combination of a 2]catenane and a 2]rotaxane, thereby combining both the circumrotation of the ring component (rotary motion) and the shuttling of the dumbbell component (translational motion) in one structure. Herein, we describe a strategy for the synthesis of a new switchable 3]rotacatenane and the investigation of its switching properties, which rely on the formation of tetrathiafulvalene (TTF) radical π-dimer interactions-namely, the mixed-valence state (TTF(2) )(+.) and the radical-cation dimer state (TTF(+.) )(2) -under ambient conditions. A template-directed approach, based on donor-acceptor interactions, has been developed, resulting in an improved yield of the key precursor 2]catenane, prior to rotacatenation. The nature of the binding between the 2]catenane and selected π-electron-rich templates has been elucidated by using X-ray crystallography and UV/Vis spectroscopy as well as isothermal titration microcalorimetry. The multistate switching mechanism of the 3]rotacatenane has been demonstrated by cyclic voltammetry and EPR spectroscopy. Most notably, the radical-cation dimer state (TTF(+.) )(2) has been shown to enter into an equilibrium by forming the co-conformation in which the two 1,5-dioxynaphthalene (DNP) units co-occupy the cavity of tetracationic cyclophane, thus enforcing the separation of TTF radical-cation dimer (TTF(+.) )(2) . The population ratio of this equilibrium state was found to be 1:1. We believe that this research demonstrates the power of constructing complex molecular machines using template-directed protocols, enabling us to make the transition from simple molecular switches to their multistate variants for enhancing information storage in molecular electronic devices. |
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Keywords: | molecular switches radical dimerization rotacatenanes template‐directed synthesis tetrathiafulvalenes |
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