Capturing Paraquats

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Science  25 Feb 2011:
Vol. 331, Issue 6020, pp. 988
DOI: 10.1126/science.331.6020.988-c

Supramolecular polymers, in which the monomer units are bound by weak interactions, could have several potential advantages over covalently bonded chains. For example, their extent of association could be temperature-dependent, so they could have lower viscosities during processing steps and assemble longer chains after cooling. However, supramolecular polymers tend to be short oligomers with only about 10 repeating units. Niu et al. report on a supramolecular polymer made from two monomers, one a conjugated chain bearing 32-crown-10 cryptand cages at both ends, and the other bearing complementary paraquat rods at both ends. When these were mixed in organic solvent, the solution turned deep yellow, reflecting charge-transfer interactions between the different monomer units. Proton nuclear magnetic resonance spectra signaled the formation of longer pseudorotaxane polymers. An analysis indicated that at concentrations of ∼0.3 molar, the polymer chains had over 40 subunits.

J. Am. Chem. Soc. 133, 10.1021/ja110384v (2011).

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