A facile route to viologen functional macromolecules through azide-alkyne [3+2] cycloaddition

Viologen end and side-chain functional macromolecules are synthesized through a high-yielding, copper-mediated azide-alkyne [3+2] cycloaddition reaction. Specifically, poly(ethylene glycol) (PEG) and the C-terminus of a model oligopeptide are quantitatively end-coupled to a viologen moiety as confirmed by (1) H NMR, gel permeation chromatography (GPC), and mass spectrometry (MS). Side-chain functionalization of a styrene backbone is also readily achieved forming a polyelectrolyte species and demonstrating the applicability of this method across a range of macromolecular species. It is found that viologen itself slows the reaction and that careful choice of counter ions, the specific chelating ligand for the copper-mediated reaction, solvent, as well as the amount of copper also play major roles in the time to completion of the reaction and hence the yield. Macromolecules formed through this route bind effectively with supramolecular host molecule cucurbit[8]uril allowing for controlled solution-phase self-assembly, for example of a supramolecular star polymer.