Chalcogen Bonding Directed Photoresponsive Helix from Azo-Fused H-Bonded Arylamide Foldamers

Abstract

In this study, a series of azo-fused H-bonded arylamide foldamers was synthesized. Molecules with extended backbones exhibited pronounced photoresponsive behavior in both dichloromethane and dimethyl sulfoxide. In low-polarity dichloromethane, intramolecular three-center hydrogen bonding remained stable, promoting the formation of well-defined S-shaped (E) and Helical (Z) conformations. In contrast, disruption of the intramolecular three-center hydrogen bonding induces a structural transition to Linear (E) and U-shaped (Z) configurations in highly polar dimethyl sulfoxide. With respect to the foldamer featuring benzoselenadiazole termini, the orthogonal interplay between intramolecular hydrogen bonding and intermolecular Se⋯N interactions synergistically drove the assembly of Linear and Helical secondary architectures, which was attributed to the inherent properties of the hydrogen-bonded arylamide foldamer combined with enhanced dual intermolecular Se⋯N chalcogen bonding. Furthermore, reversible structural interconversion was achieved through alternating irradiation at 365 nm and 600 nm. The conformational dynamics and structural transformations were rigorously characterized and computationally validated using nuclear magnetic resonance (NMR) and UV–Vis spectroscopy, as well as density functional theory (DFT) calculations, and molecular dynamics (MD) simulations. This work presents an innovative supramolecular helical self-assembly directed by noncovalent interactions, wherein the resulting helices demonstrate distinctive photoresponsive properties.