Fzbrication Of Photoseitchable Host-Guest Systems On Surfaces Based On Azobenzene And β-CD

For the cis-trans photoisomerization of azobenzene, the host-guest recognition between cyclodextrin and the photoresponsive polymer Azo had been utilized in supramolecular assembly, vesicles, photoresponsive molecularly imprinted systems, photoresponsive smart templates, and surface switchable host-guest systems. Although many molecular devices satisfactorily function in solutions, problems arise when they are transferred onto solid surfaces. Hence, fabrication of multifunctional surfaces with azobenzene faces significant challenges, and has been the focus of scientific studies over the previous years. Although photoswitchable host-guest systems on surfaces have been obtained by many surfacemodification methods, the process to fabricate the film on the surface requires harsh conditions and complex reactions, resulting in inefficient polymerization reactions, and the photoisomerization of azobenzene was always inefficient because of the steric hindrance effects. In this work, the photoswitchable host-guest systems on surfaces based on azobenzene and β-CD had been constructed via two facile methods namely two-stage photopolymerization and Au-S self-assembly. The main work was as follows:(1) A responsive surface could be easily built by combiningchemical composition and two different trigger mechanisms ofphotopolymerization namely cleavage and hydrogen abstraction. Inthis study, stimuli-responsive polymers PDMAEMA and 2-methyl-4-phenylazo acrylate (MPA-Azo) were prepared on a surface byutilizing a facile and moderate two-stage photopolymerization method.In stage I, PDMAEMA containing tertiary amine groups, which could be used as a co-initiator for a type Ⅱ photo-initiator, was grafted on the silanization surface. In stage II, the type II photoinitiator(ITX) was used and MPA-Azo wasgrafted on the amine groups of the PDMAEMA network throughtype II photopolymerization. Afterwards, the classic host-guestrecognition self-assembly of MPA-Azo and β-CD was conducted atdifferent light wavelengths.(2) Thiol-functionalized long alkyl chain azobenzene polymer has been synthesized by esterification reaction, Au nanoparticles of 14 nm were prepared by citrate reduction of HAuCl4 in aqueous phase, and the silicon substrate modified with β-CD was constructed by Michael addition reaction. Au-S-Azo nanoparticles were prepared by facile ligand exchange between AuNPs with HS-Azo in ethanolic solution.Liquid-solid reversible phase transfer of AuNPs with azobenzene-containing could be conducted based on host-guest interaction between P-CD and azobenzene by irradiation with UV and visible light. This work will have extensive potential application in the recovery and recycling of the gold nanoparticles and have significant impact on nanomaterials phase transfer between solution and solid.