The self-assembly of single chain Janus nanoparticles from azobenzene-containing block copolymers and reversible photoinduced morphology transitions

The self-assembly of amphiphilic single chain Janus nanoparticles (SCJNPs) is a novel and promising approach for fabricating assemblies with diversified morphologies. However, experimental research into the self-assembly behavior of SCJNPs is still limited. Furthermore, it is desirable to broaden the functionality of assemblies of SCJNPs. Herein, we constructed photoresponsive liquid crystalline (LC) SCJNPs through the intrachain photo-cross-linking of azobenzene-containing amphiphilic linear block copolymer precursors of poly(poly(ethylene glycol)methyl ether methacrylate)-b-poly(11-(4-((4-butylphenyl)diazenyl)phenoxy)undecyl methacrylate-co-11-(4-(4-butylstyryl)phenoxy)undecyl methacrylate). The self-assembly behavior of these LC-SCJNPs in solution was investigated via controlling the block copolymer (BCP) composition and initial concentration. Under the effect of the LC driving force, non-spherical assemblies, including lamellae and tubes, were obtained. Additionally, the photoinduced morphological transformations of assemblies with various azobenzene contents were studied via irradiation with alternative UV/vis light irradiation. Owing to the azobenzene moieties tethered within the SCJNP building blocks via intrachain cross-linking, reversible photoinduced morphology transitions of tubes-connected spheres-tubes and spherical vesicles-spheres-spherical vesicles were observed for assemblies with a higher azobenzene content. This work broadens the functionality and self-assembly systems of SCJNPs, providing a novel view of the photoinduced morphological transitions of assemblies from SCJNPs.