A Tetracationic Cyclophane

A tetracationic macrocycle namely ExBluebox⁴⁺ bearing two N-phenylene-bipyridinium units that are bridged in a face-to-face manner by two rigid linkers was synthesized by using an electron rich template. Compared to the so-called “ Bluebox⁴⁺” first invented by Stoddart, ExBluebox⁴⁺ reported here has an extended cavity, allowing the recognition of guests whose sizes exceed the inner cavity of Bluebox⁴⁺. In comparison with the so-called “ Exbox⁴⁺” in which two pyridinium units are separated by a phenylene linker, the viologen dications in ExBluebox⁴⁺ remain intact. ExBluebox⁴⁺ demonstrates capabilities of recognizing various aromatic guests in both water and organic solvent such as MeCN. By taking advantage of the difference in binding affinities, the macrocycle dissolved in water was able to separate pyrene from perylene, whose separation would be otherwise rather difficult due to their similar physical properties such as boiling points. In water, ExBluebox⁴⁺ can be recognized within the cavity of cucurbit[10]uril (CB[10]), forming a complex ExBluebox⁴⁺⊂CB[10], driven by hydrophobic effect and cation-dipole interactions. After encapsulated within of CB[10], the guest recognition ability of ExBluebox⁴⁺ lived on or even rose in water, allowing the self-assembly of "Russian doll" structures in the form of guest⊂ ExBluebox⁴⁺⊂CB[10].

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