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Ground-State Equilibrium Thermodynamics and Switching Kinetics of Bistable [2]Rotaxanes Switched in Solution, Polymer Gels, and Molecular Electronic Devices

Authors

  • Jang Wook Choi,

    1. Division of Chemistry and Chemical Engineering (127–72), California Institute of Technology, 1200 E. California Blvd. Pasadena, CA, 91125, USA, Fax: (+1) 626-395-2355
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  • Amar H. Flood Dr.,

    1. California NanoSystems Institute and Department of Chemistry and Biochemistry, University of California, Los Angeles, 405 Hilgard Avenue, Los Angeles, CA, 90095-1569, USA, Fax: (+1) 310-206-1843
    2. Current Address: Department of Chemistry, Indiana University, 800 East Kirkwood Avenue, Bloomington, IN 47405, USA
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  • David W. Steuerman Dr.,

    1. Division of Chemistry and Chemical Engineering (127–72), California Institute of Technology, 1200 E. California Blvd. Pasadena, CA, 91125, USA, Fax: (+1) 626-395-2355
    2. Current Address: Department of Physics, University of California, Santa Barbara CA 93106, USA
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  • Sune Nygaard,

    1. Department of Chemistry, Odense University (University of Southern Denmark), Campusvej 55, 5230, Odense M, Denmark, Fax: (+45) 66-15-87-80
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  • Adam B. Braunschweig,

    1. California NanoSystems Institute and Department of Chemistry and Biochemistry, University of California, Los Angeles, 405 Hilgard Avenue, Los Angeles, CA, 90095-1569, USA, Fax: (+1) 310-206-1843
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  • Nicolle N. P. Moonen Dr.,

    1. California NanoSystems Institute and Department of Chemistry and Biochemistry, University of California, Los Angeles, 405 Hilgard Avenue, Los Angeles, CA, 90095-1569, USA, Fax: (+1) 310-206-1843
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  • Bo W. Laursen Dr.,

    1. California NanoSystems Institute and Department of Chemistry and Biochemistry, University of California, Los Angeles, 405 Hilgard Avenue, Los Angeles, CA, 90095-1569, USA, Fax: (+1) 310-206-1843
    2. Current Address: Nano-Science Center, University of Copenhagen, Universitetsparken 5, 2100, København Ø, Denmark
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  • Yi Luo Dr.,

    1. Division of Chemistry and Chemical Engineering (127–72), California Institute of Technology, 1200 E. California Blvd. Pasadena, CA, 91125, USA, Fax: (+1) 626-395-2355
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  • Erica DeIonno,

    1. Division of Chemistry and Chemical Engineering (127–72), California Institute of Technology, 1200 E. California Blvd. Pasadena, CA, 91125, USA, Fax: (+1) 626-395-2355
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  • Andrea J. Peters Dr.,

    1. California NanoSystems Institute and Department of Chemistry and Biochemistry, University of California, Los Angeles, 405 Hilgard Avenue, Los Angeles, CA, 90095-1569, USA, Fax: (+1) 310-206-1843
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  • Jan O. Jeppesen Prof.,

    1. Department of Chemistry, Odense University (University of Southern Denmark), Campusvej 55, 5230, Odense M, Denmark, Fax: (+45) 66-15-87-80
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  • Ke Xu,

    1. Division of Chemistry and Chemical Engineering (127–72), California Institute of Technology, 1200 E. California Blvd. Pasadena, CA, 91125, USA, Fax: (+1) 626-395-2355
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  • J. Fraser Stoddart Prof.,

    1. California NanoSystems Institute and Department of Chemistry and Biochemistry, University of California, Los Angeles, 405 Hilgard Avenue, Los Angeles, CA, 90095-1569, USA, Fax: (+1) 310-206-1843
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  • James R. Heath Prof.

    1. Division of Chemistry and Chemical Engineering (127–72), California Institute of Technology, 1200 E. California Blvd. Pasadena, CA, 91125, USA, Fax: (+1) 626-395-2355
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Abstract

We report on the kinetics and ground-state thermodynamics associated with electrochemically driven molecular mechanical switching of three bistable [2]rotaxanes in acetonitrile solution, polymer electrolyte gels, and molecular-switch tunnel junctions (MSTJs). For all rotaxanes a π-electron-deficient cyclobis(paraquat-p-phenylene) (CBPQT4+) ring component encircles one of two recognition sites within a dumbbell component. Two rotaxanes (RATTF4+ and RTTF4+) contain tetrathiafulvalene (TTF) and 1,5-dioxynaphthalene (DNP) recognition units, but different hydrophilic stoppers. For these rotaxanes, the CBPQT4+ ring encircles predominantly (>90 %) the TTF unit at equilibrium, and this equilibrium is relatively temperature independent. In the third rotaxane (RBPTTF4+), the TTF unit is replaced by a π-extended analogue (a bispyrrolotetrathiafulvalene (BPTTF) unit), and the CBPQT4+ ring encircles almost equally both recognition sites at equilibrium. This equilibrium exhibits strong temperature dependence. These thermodynamic differences were rationalized by reference to binding constants obtained by isothermal titration calorimetry for the complexation of model guests by the CBPQT4+ host in acetonitrile. For all bistable rotaxanes, oxidation of the TTF (BPTTF) unit is accompanied by movement of the CBPQT4+ ring to the DNP site. Reduction back to TTF0 (BPTTF0) is followed by relaxation to the equilibrium distribution of translational isomers. The relaxation kinetics are strongly environmentally dependent, yet consistent with a single electromechanical-switching mechanism in acetonitrile, polymer electrolyte gels, and MSTJs. The ground-state equilibrium properties of all three bistable [2]rotaxanes were reflective of molecular structure in all environments. These results provide direct evidence for the control by molecular structure of the electronic properties exhibited by the MSTJs.

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