Light-Induced Reversible Hierarchical Self-Assembly of Amphiphilic Diblock Copolymers into Microscopic Vesicles with Tunable Optical and Nanocarrier Properties

In contrast to the conventional hierarchical self-assembly process, effective methods to enable reversible hierarchical self-assembly of block copolymers are comparatively few and limited in scope. Herein, we report, for the first time, a simple yet robust strategy for light-induced reversible hierarchical self-assembly of an amphiphilic diblock copolymer, poly(4-vinylpyridine)-block-poly[6-[4-(4-butyloxyphenylazo)phenoxy]hexyl methacrylate] (denoted P4VP-b-PAzoMA). The hierarchical structures are constructed via a two-step self-assembly process (first-level reverse micelles, second-level compound micelles, and rearrangement into micrometer-sized vesicles) driven by use of solvent. Intriguingly, because of reversible photoinduced trans-to-cis isomerization of azobenzene moieties in PAzoMA, the vesicles could disassemble into subunits upon UV light and then recover the nearly identical vesicular morphology upon visible light. Such a reversible hierarchical self-assembly process is accompanied by reversible fluorescence, encapsulation, and controlled release of dyes and can be used as a template for the synthesis of nanoparticles. Clearly, the ability to render the light-enabled reversible hierarchical self-assembly provides a unique platform for smart delivery vehicles and templates for nanomaterials.