Study On Assembled Superstructures And Fluorescence Properties Of Host-Guest Complexes Based On Trialkoxy Azobenzene Derivatives And Poly(Phenylene Ethynylene) Conjugated Polymers With Pillararene Side Groups

One of the most intriguing properties of azobenzene is the photoisomerization of trans and cis isomers. The two isomers can be switched under light irradiation of particular wavelengths. This property can be used in the field of optical information storage, nonlinear optical materials, liquid crystal molecular orientation, and light-driven smart materials. In recent years, pillararenes as novel macrocycle host compounds have aroused broad attention in supramolecualr host-guest assembly for their highly symmetrical character and cavity structure, such as in preparation of supramolecular polymers, nanotubes, vesicles and other interesting supramolecular systems. The cavity structure of pillar[6]arene fits well in size with azobenzene chromophore, so a variety of photoresponsive supramolecular systems can be built based on host-guest assembly.In this thesis, the assembly superstructures and fluorescence properties based on host-guest self-assembly of azobenzene derivatives and conjugated polymers with pillararene side groups have been studied. The self-assembly behaviors and morphology changes of amphiphilic azobenzene derivatives with quaternary ammonium group in solution have also been investigated. The contents and main results are summarized as follows:1. A series of trialkoxy azobenzene derivatives with different carbon chain lengths have been designed, synthesized and systematically characterized. Referenced and modified from literature method, an improved method was employed to establish amide between amino and ester groups of the reactants for synthesizing the target azobenzene products with reduced reaction steps, milder reaction conditions and enhanced yields. An amphiphilic trialkoxy azobenzene compound with quaternary quaternary ammonium end group has also been synthesized.2. The self-assembly superstructures of conjugated polymers with pillararene side groups and trialkoxy azobenzene in bulk have been studied. It showed that the pillar[5]arene with small cavity size formed weakly complexed self-assembly structures with azobenzene group and dissociation occurred warming to 58℃, while the pillar[6]arene cavity size fits well with the azobenzene group, much more stable self-assembly superstructures were formed, a tetragonal columnar ordered structure was constructed as confirmed by SAXS after prolonged annealing.3. The poly(phenylene ethynylene) main chain of pillar[6] arene side-chain conjugated polymer has a strong fluorescence emission in CH2CI2 solution. While the fluorescence was quenched due to FRET effect between the poly(phenylene ethynylene) and azobenzene when the host-guest complex formed between azobenzene and pillar[6]arene once trialkoxy azobenzene derivative was added. The binding constant of pillar[6]arene and trialkoxy azobenzene has been estimated to be 0.76 x 103 L/mol with the fluorescence quenching. The fluorescence emission recovered upon the disassembly when the azobenzene group was transformed from trans into cis by 365 nm UV irradiation.4. The assembly behaviors and morphology changes of amphiphilic trialkoxy azobenzene derivatives with quaternary ammonium end group in n-hexane/CH2Cl2 or THF/H2O solution have also been investigated. As confirmed by TEM observation that bilayered sturctures were mainly formed in n-hexane/CH2Cl2 solution, and after 365 nm UV irradiation, the assemblage changed into vesicles in the solution of 40% volume CH2Cl2. When the water volume percentage is 50% in THF/H2O solution, the self-assembly structure was found to be single layer lamellar structure and transform into vesicles after 365nm UV irradiation. While when the water volume percentage reached 90%, the assembled structures were vesicles and dissociated into bilayered structures after 365nm UV irradiation.