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Published August 28, 2013 | Supplemental Material
Journal Article Open

Ex^2Box: Interdependent Modes of Binding in a Two-Nanometer-Long Synthetic Receptor


Incorporation of two biphenylene-bridged 4,4′-bipyridinium extended viologen units into a para-phenylene-based cyclophane results in a synthetic receptor that is 2 nm long and adopts a box-like geometry. This cyclophane, Ex^2Box^4+, possesses the ability to form binary and ternary complexes with a myriad of guest molecules ranging from long π-electron-rich polycyclic aromatic hydrocarbons, such as tetracene, tetraphene, and chrysene, to π-electron-poor 2,6-dinitrotoluene, 1,2,4-trichlorobenzene, and both the 9,10- and 1,4-anthraquinone molecules. Moreover, Ex^2Box^4+ is capable of forming one-to-one complexes with polyether macrocycles that consist of two π-electron-rich dioxynaphthalene units, namely, 1,5-dinaphtho[38]crown-10. This type of broad molecular recognition is possible because the electronic constitution of Ex^2Box^4+ is such that the pyridinium rings located at the "ends" of the cyclophane are electron-poor and prefer to enter into donor–acceptor interactions with π-electron-rich guests, while the "middle" of the cyclophane, consisting of the biphenylene spacer, is more electron-rich and can interact with π-electron-poor guests. In some cases, these different modes of binding can act in concert to generate one-to-one complexes which possess high stability constants in organic media. The binding affinity of Ex^2Box^4+ was investigated in the solid state by way of single-crystal X-ray diffraction and in solution by using UV–vis and NMR spectroscopy for 12 inclusion complexes consisting of the tetracationic cyclophane and the corresponding guests of different sizes, shapes, and electronic compositions. Additionally, density functional theory was carried out to elucidate the relative energetic differences between the different modes of binding of Ex^2Box^4+ with anthracene, 9,10-anthraquinone, and 1,4-anthraquinone in order to understand the degree with which each mode of binding contributes to the overall encapsulation of each guest.

Additional Information

© 2013 American Chemical Society. Received: May 25, 2013; Published: July 18, 2013. The data reported are tabulated in the Supporting Information and the crystallographic parameters of each single crystal were deposited into the Cambridge Crystallographic Data Centre (CCDC). The research at Northwestern University (NU) was enabled by the National Center for Nano Technology Research at the King Abdulaziz City for Science and Technology (KACST) in Saudi Arabia. The authors thank Dr. Turki S. Al-Saud and Dr. Nezar H. Khdary at KACST for their interest in this research. J.F.S. is supported by the Non-Equilibrium Energy Research Center (NERC), which is an Energy Frontier Research Center (EFRC) funded by the U.S. Department of Energy, Office of Basic Energy Sciences (DOE-BES) under award DESC0000989. M.J. gratefully acknowledges The Netherlands Organization for Scientific Research (NWO) and the Marie Curie Cofund Action (Rubicon Fellowship). J.C.B. is supported by a National Defense Science and Engineering Graduate Fellowship (32 CFR 168a) from the Department of Defense (DoD) and gratefully acknowledges receipt of a Ryan Fellowship from the NU International Institute for Nanotechnology (IIN). E.J.D., N.L.S., and C.J.B. are supported by a Graduate Research Fellowship (GRF) from the National Science Foundation (NSF).

Attached Files

Supplemental Material - ja4052763_si_001.pdf

Supplemental Material - ja4052763_si_002.cif

Supplemental Material - ja4052763_si_003.cif

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