Visualizing molecular weights differences in supramolecular polymers.

Issues of molecular weight determination have been central to the development of supramolecular polymer chemistry. Whereas relationships between concentration and optical features are established for well-behaved absorptive and emissive species, for most supramolecular polymeric systems no simple correlation exists between optical performance and number-average molecular weight ( M n ). As such, the M n of supramolecular polymers have to be inferred from various measurements. Herein, we report an anion-responsive supramolecular polymer [M1·Zn(OTf) 2 ] n that exhibits monotonic changes in the fluorescence color as a function of M n Based on theoretical estimates, the calculated average degree of polymerization (DP cal ) increases from 16.9 to 84.5 as the monomer concentration increases from 0.08 mM to 2.00 mM. Meanwhile, the fluorescent colors of M1 + Zn(OTf) 2 solutions were found to pass from green to yellow and to orange, corresponding to a red shift in the maximum emission band ( λ max ). Therefore, a relationship between DP cal and λ max could be established. Additionally, the anion-responsive nature of the present system meant that the extent of supramolecular polymerization could be regulated by introducing anions, with the resulting change in M n being readily monitored via changes in the fluorescent emission features.