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

Abstract

The uniformity and tunable ring size of toroidal nanostructures are promising in many fields but still challenging. Herein, polyolefin-based homopolymers with pyridinium cation junctions between the main chain parts and alkyl azobenzene pendants were systematically synthesized and further self-assembled into preformed spheres based on the multiple effects of solvophobic backbone, electrostatic force and strong non-covalent aromatic–aromatic interaction. Subsequently, UV-light-triggered shackling trans→cis photoisomerization transition was demonstrated, meanwhile, the uniform toroids with stable shape and adjustable dimension were observed after continuously irradiating UV-light and eventually reaching the photostationary state. The mechanistic investigation further confirmed that the strong non-covalent interaction generated during the significantly confined photoisomerization process is essential for the formation of polymeric toroid. Importantly, the toroidal morphology is insusceptible to the used solvent system, but the ring size can be optionally adjusted from nanoscale to microscale. We expect that the importance of regulation multiple non-covalent interactions in reinforcing each other will offer a new avenue to induce self-assembly of homopolymer to produce the uniform and particular morphology.