Polymeric toroidal assemblies formed from ionic homopolymers with shackling photo-responsive behavior

Abstract

The uniformity of toroidal nanostructures and their tunable ring sizes give them promise for applications in many fields, but their synthesis remains challenging. Herein, polyolefin-based homopolymers with pyridinium cation junctions between the main chain and alkyl azobenzene pendant groups were systematically synthesized and self-assembled into preformed spheres due to the solvophobic backbone and electrostatic and strong non-covalent aromatic–aromatic interactions present in the homopolymers. Subsequently, UV light-triggered shackling of the trans → cis photoisomerization transition was demonstrated, and subsequently, uniform toroids with stable shapes and adjustable dimensions were observed after continuously irradiating with UV light to eventually reach the photostationary state. A mechanistic investigation further confirmed that the strong non-covalent interactions generated during the significantly confined photoisomerization process are essential for the formation of the polymeric toroids. Importantly, the toroidal morphology is not susceptible to the solvent system used, but the ring size can be optionally adjusted from the nanoscale to the microscale by varying other factors. We expect that the importance of the regulation of the different non-covalent interactions in reinforcing each other will offer a new avenue to induce self-assembly of homopolymers to produce uniform and specific morphologies.