Folding of aromatic polyamides into a rare intrachain β-sheet type structure and further reinforcement of the secondary structure through host–guest interactions

Abstract

Aromatic oligoamides have been shown to adopt various secondary structures, such as helical structures, linear strands, etc., but synthetic β-sheet structures are not well known. Here we demonstrate the intrachain β-sheet like folded structure of aromatic polyamides. Precise placement of H-bonding and π-stacking motifs along the polymer chain was necessary for the folding process. The control polymer without intramolecular H-bonding motifs assumed a random-coil structure. Unfolding of the polymer was observed at higher temperatures; however, the presence of π-surface containing guest molecules improved the thermal stability of the folded structure through co-facial host–guest π-stacking interactions. The possible applications of these molecules as through-space electron-conducting materials, organocatalysts, etc. can be envisaged.