Preparation Of Azobenzene-containing Photo-responsive Materials By The Way Of Superamolecular Self-assembly

Azobenzene undergoes reversible trans-cis isomerization with stimulation of light or heat, which makes it an ideal candidate for molecular devices or functional materials. Superamolecular assemble is one of the important methods to fabricate nanostructured materials. Azobenzene-containing amphiphilic molecules can self-assemble into various micelles with photo-induced properties, which have promising applications in drug-delivery, light-driven reactors, biodiagnostics, and so on. Although, recent years, the azobenzene-containing amphiphilic polymers and surfactants have attracted wide attention and developed rapidly, there are some disadvantages(e.g. the complicated synthetic routes, difficult control of molecular sequential structure) for the former. Additionally, for some important micellar structure such as tubes, helical ribbons and so on, the formation mechanism and preparation conditions are still in the stage of exploration. This dissertation aims at exploring simple and efficient methods of polymerization to synthesize polymers bearing regulated azobenzene groups, and investigating the self-assembly of the azobenzene-containing polymer and photo-induced property of the assembies. Moreover, efforts have been made to prepare the azobenzene-containing nanostructure with photo-reponsive properties,and study the mechanism of the formation or transition.Firstly, we have synthesized a polymer bearing regulated azobenzene groups by one-pot multi-component polymerization(MCP-azo-OH) based on Passerini reaction, and investigated the self-assembly behavior and photo-induced deformation properties. We found that this compound can form spherical structures when being dissolved in THF. NMR and FTIR spectra indicate that there are intermolecular hydrogen bonds among the molecules in the aggregates, which is responsible for the formation of the nanospheres. By controlling the stirring rate as dropping the THF suspension into water, the nanospheres can be sorted according to the size, and the smaller nanospheres can be obtain at the higher stirring rate. When irradiated by the UV light in the aqueous medium, the nanospheres tend to aggregate into large clusters; while in dry state, they are ready to merge into island-like structures, showing a good photo-induced deformation property.Secondly, a kind of achiral azobenzene-containing long chain fatty acid(ABA11) has been prepared, and this molecule can self-assemble into nanotubes with uniform diameter. TEM, XRD and FITR data indicate that the wall of nanotube is composed of the bilayer of the molecules, which is a result of the hydrogen bonds between carboxylic groups. What’s more, by controlling the incubation temperature and time, the aggregates can go through a morphology evolution from membrane, ribbons, helical ribbons to nanotubes. All the structures mentioned in the theoretical model of tube formation proposed by Selinger et al can be observed in the same system, and the process of transformation is quite consistent with the theory. Thus this study provides experimental support to the theory.