Helical Self-Assembly of Amphiphilic Chiral Azobenzene Alternating Copolymers

Imposing chirality to supramolecular architectures is an important step forward toward understanding and utilization of chiral nanomaterials. This article reports the self-assembly of amphiphilic chiral alternating copolymers of poly(binaphthyl azobenzene-alt-hexaethylene glycol) (P(BNPAzo-alt-EG₆)) into helical supramolecular rods. Unlike conventional chiral assembly of copolymers largely through intermolecular organization, the intrachain stacking of chiral units along the main chain into single molecular micelles with amplified axial chirality of binaphthyl is key to the formation of helical supramolecular rods, which takes advantage of the particular chiral unit and soft unit alternating topological structure of the backbones. Moreover, the supramolecular self-assembly is light reversible because the azobenzene rings in the backbone scarcely execute trans- to cis-isomerization upon UV irradiation, and therefore the supramolecular rods keep their sublevel chirality even though the helical appearance was destroyed. This work paves an effective route to construct and regulate chiral supramolecular architectures and reveals an insight into natural and artificial chiral self-assembly.