Linear Dichroism Activity of Chiral Poly(p-Aryltriazole) Foldamers

Abstract

Controllable higher-order assembly is a central aim of macromolecular chemistry. An essential challenge to developing these molecules is improving our understanding of the structures they adopt under different conditions. Here, we demonstrate how flow linear dichroism (LD) spectroscopy is used to provide insights into the solution structure of a chiral, self-assembled fibrillar foldamer. Poly(para-aryltriazole)s fold into different structures depending on the monomer geometry and variables such as solvent and ionic strength. LD spectroscopy provides a simple route to determine chromophore alignment in solution and is generally used on natural molecules or molecular assemblies such as DNA and M13 bacteriophage. In this contribution, we show that LD spectroscopy is a powerful tool in the observation of self-assembly processes of synthetic foldamers when complemented by circular dichroism, absorbance spectroscopy, and microscopy. To that end, poly(para-aryltriazole)s were aligned in a flow field under different solvent conditions. The extended aromatic structures in the foldamer give rise to a strong LD signal that changes in sign and in intensity with varying solvent conditions. A key advantage of LD is that it only detects the large assemblies, thus removing background due to monomers and small oligomers.