Photo-responsive supramolecular self-assembly and disassembly of an azobenzene-containing block copolymer

An azobenzene-containing block copolymer poly(ethylene oxide)-b-poly(6-[4-phenylazo phenoxy] hexyl methacrylate-co-2-(dimethylamino) ethyl methacrylate) (PEO-b-P(AzoMA-co-DMAEMA)) was successfully designed to explore self-assembly behavior in an aqueous solution. PEO-b-P(AzoMA-co-DMAEMA) can self-assemble into vesicles in water. The morphologies and sizes of the vesicles can be controlled by copolymerization of hydrophobic AzoMA with different amounts of DMAEMA. Spherical vesicle-to-compound vesicle-to-irregular vesicle transitions were observed by facilely adjusting the content of DMAEMA and AzoMA. After the addition of different amounts of beta-CD, vesicles were transformed into micelles and at last dissociated. Alternating irradiation of the solution with UV and visible light induced the reversible supramolecular self-assembly and disassembly of vesicles because of the photo-induced trans-to-cis isomerization of azobenzene units. The supramolecular self-assembly and disassembly procedure was studied by dynamic light scattering (DLS), transmission electron microscopy (TEM) and UV-vis spectra.