Visible-Light-Responsive Shackling Hyperbranched Azo-Ionomers with Photo-controllable Self-Assembly Behavior

A novel visible-light-controllable self-assembly system was produced by employing three kinds of novel ionic hyperbranched azo-polymers (IHBAPs), which were synthesized via one-step acyclic diene metathesis polymerization of ionic AB2 azo-monomers based on modifying the synthetic procedure. Compared to the traditional azo-polymers, UV–vis spectra showed significant red shifts (429–441 nm) of the maximum absorption peaks and, in particular, all visible-light-activated shackling trans → cis isomerization transition of azo chromophores in IHBAPs. Taking advantage of this characteristic of IHBAPs, a series of photosensitive nanosphere morphologies were constructed, which further drove the morphological transformation to produce shape-recoverable shuttle-like and worm-like nanoaggregates after alternating exposure to 465 nm blue light and 625 nm red light. Importantly, nanospheres were insusceptible to the solvent system used but could evolve into nanorods and irregularly branched and cloud-like nanostructures at different concentrations under continuous illumination of blue light. Moreover, the enhanced self-assembly concentration will promote these nanospheres to stack from one dimension to three dimensions, eventually forming large irregular nanoaggregates. This study not only demonstrates the typical example of light-responsive nonlinear azo-ionomers but also opens a new avenue for controlling morphological transformation and restoration by visible light.