Self-Assembly and Photoinduced Spindle-Toroid Morphology Transition of Macromolecular Double-Brushes with Azobenzene Pendants

Asymmetric macromolecular double-brushes (MDBs) are composed of two different side chains grafted on a linear backbone, possessing distinct assembly behaviors in comparison with conventional amphiphiles, owing to the Janus architecture and combined effects of backbone and hetero double-brushes. Additionally, the introduction of unique functionalities and responsiveness into the self-assembly system of MDBs endows extra opportunities to pursue morphologic diversity and intriguing properties. Herein, we report the synthesis of Janus-like MDBs of polyacrylate-g-poly(6-(4-butyl-4'-oxyazobenzene) hexyl acrylate)/poly(ethylene oxide) (PA-g-PAzo/PEO), in which hydrophilic PEO and hydrophobic PAzo brushes were grafted using the combination of concurrent ATRP and click reaction. Due to the special Janus topology and inter/intramolecular association of pendant azobenzene groups, amphiphilic PA-g-PAzo/PEO self-assembled into multimolecular rod and spindle-like aggregates. It is interesting that a transition of spindle-toroid-spindle was observed upon the alternative irradiation between UV and visible light, which is ascribed to the trans-to-cis isomerization of azobenzene molecular brushes. To our best knowledge, this is the first time that azobenzene-containing MDBs enable the fabrication of distinctive self-assembled morphologies and photoinduced toroid formation. The controlled synthesis of MDBs with unique functionalities and subsequent development of their structure-property relationships would shed light on the design and optimization of bottlebrush-based nanomaterials.