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Donor–Acceptor Ring-in-Ring Complexes

Authors

  • Dr. Ross S. Forgan,

    1. Center for the Chemistry of Integrated Systems and Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3133 (USA), Fax: (+1) 847-491-1009
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    • These authors contributed equally to this work.

  • Dr. Cheng Wang,

    1. Center for the Chemistry of Integrated Systems and Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3133 (USA), Fax: (+1) 847-491-1009
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    • These authors contributed equally to this work.

  • Dr. Douglas C. Friedman,

    1. Center for the Chemistry of Integrated Systems and Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3133 (USA), Fax: (+1) 847-491-1009
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  • Dr. Jason M. Spruell,

    1. Center for the Chemistry of Integrated Systems and Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3133 (USA), Fax: (+1) 847-491-1009
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  • Charlotte L. Stern,

    1. Center for the Chemistry of Integrated Systems and Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3133 (USA), Fax: (+1) 847-491-1009
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  • Dr. Amy A. Sarjeant,

    1. Center for the Chemistry of Integrated Systems and Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3133 (USA), Fax: (+1) 847-491-1009
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  • Dennis Cao,

    1. Center for the Chemistry of Integrated Systems and Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3133 (USA), Fax: (+1) 847-491-1009
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  • Prof. J. Fraser Stoddart

    Corresponding author
    1. Center for the Chemistry of Integrated Systems and Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3133 (USA), Fax: (+1) 847-491-1009
    2. NanoCentury KAIST Institute and Graduate School of EEWS, Korea Advanced Institute of Science and Technology (KAIST), 373-1, Guseong Dong, Yuseong Gu, Daejeon 305-701 (Republic of Korea)
    • Center for the Chemistry of Integrated Systems and Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3133 (USA), Fax: (+1) 847-491-1009
    Search for more papers by this author

Abstract

The self-assembly of three donor–acceptor ring-in-ring complexes, prepared from the π-electron-deficient tetracationic cyclophane, cyclobis(paraquat-4,4′-biphenylene), and three large π-electron-rich crown ethers (each 50-membered rings) containing dioxynaphthalene (DNP) and tetrathiafulvalene (TTF) units in pairs (DNP/DNP, DNP/TTF and TTF/TTF), is reported. 1H NMR spectroscopic analyses are indicative of the formation of 1:1 complexes in CD3CN, whilst the charge-transfer interactions between the DNP and TTF units of the crown ethers and the tetracationic cyclophane have permitted the measurement of binding constants of up to 4×103M−1 in CH3CN to be made using UV/Vis spectroscopy. Ring-in-ring complexes are proposed as intermediates in the stepwise synthesis of molecular Borromean rings (BRs) comprised of three different rings. With the particular choice of crown ethers, the 1:1 complexes have polyether loops that protrude from the donor–acceptor recognition point above and below the mean plane of the tetracationic cyclophane, which, ideally, could conceivably bind dialkylammonium centers present in a third ring. X-ray crystallographic analyses of the solid-state superstructures of two of the three 1:1 complexes reveal, however, the presence of prodigious CH⋅⋅⋅O interactions between the polyether loops of the crown ethers and the rims of the cyclophane, no doubt stabilizing the complexes, but, at the same time, masking their potential recognition sites from further interactions that are essential to the subsequent emergence of the third ring. The solid-state superstructure of one of the crown ethers binding two dibenzylammonium ions provides some insight into the design requirements for the next generation of these systems; longer polyether loops may be required to allow optimal interactions between all components. It has become clear during a pursuit of the stepwise synthesis of the molecular BRs that, when designing complex mechanically interlocked molecules utilizing multiple recognition sites, the unsullied orthogonality of the recognition motifs is of the utmost importance.

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