Preparation, Optical Properties And Application Of Thermoresponsive Polymer Ligand Functionalized Fluorescent Hybrid Nanoparticles Systems

Fluorescent nanoparticles(NPs), including semiconductor NPs(Quantum Dots) and metal NPs(or nanoclusters), have been a major focus of research and development during the past decade. Because these NPs exhibit unique properties associated with optical and electrical behaviors, which are different from the properties in their bulk materials. The fluorescent nanoparticles show unique chemical and optical properties, such as high fluorescence quantum yields, higher photostability and size-dependent emission wavelength, compared to classical fluorescent organic dyes. Moreover, the nanoparticles can also act as multivalent scaffolds for functionalization with multi-functional polymer ligand due to their high surface to volume ratio. Fluorescent NPs/polymer ligand hybrids are appealing opto-electronic materials due to the possibility of combining desired properties from both components in one, thus creating new properties that may not be present in each individual material. Collective properties of hybrid NPs can build the foundation for constructing hybrid nanocomposites with unlimited possibilities.In this thesis, QDs and gold NPs are chosed as scaffolds to be functionalized with muti-functional thermoresponsive polymer ligands by coordination interactions. Thus, we can construct a new type of multi-functional integrated fluorescent NPs/polymer hybrid systems with the emission tailor-made, controllable self-assembled morphology, thermoresponsive and environmentally sensitive properties. The detailed content and novelties of this thesis include:(1) Novel thermoresponsive Cd Te/Zn S quantum dots(QDs) decorated with a random copolymer ligand(CPL) containing 8-hydroxyquinoline and NIPAM units were prepared through coordinate bonding in aqueous solution. The dependence of the morphology and optical properties of the QDs/CPL assemblies formed via coordinate bonding on the experimental conditions were studied. The CPL functionalized QDs exhibited independent double channel emission from the cooperating interaction between the inherent emission(606 nm) of the QDs and the surface-coordinated emission(517 nm) of the CPL complex formed on the QD surface. The thermoresponsive QDs/CPL assemblies also exhibited dual reversible PL properties between the inherent emission of QDs and surface-coordinated emission by the modulation of temperature. A ratiometric fluorescent probe based on dual luminescence QD/CPL for selective sensing of the nitroaromatic explosive of picric acid(PA) was constructed. The observed ratiometric fluorescence intensity change allowed the quantitative detection of PA with a detection limit of 9nm.(2) Blue light emitting gold nanoparticles(Au NPs) decorated with CPL were prepared by both the “top-down” and the “bottom-up” approaches. The Au NPs obtained from p H induced reduction method exhibited interesting coordinate induced self-assemblies and aggregation-induced emission enhancement(AIEE) effect. The mechanism study of blue light emission of Au NPs suggested that the emission should result from a ligand-to-metal charge transfer transition. The observed fluorescence intensity decreasing of CPL capped Au NPs allowed the quantitative detection of mercury(II) in aqueous solution with a detection limit of 0.9 n M. The novel Au NPs with low cytotoxicity were used in the in vitro researches of the fluorescence imaging of cells.(3) A novel random copolymer ligand(S-CPL) containing 2,3-epithiopropylmethacrylate and NIPAM units were prepared as thermoresponsive polymer ligand, which was further employed as scaffolds to in-situ prepare of different size and morphology of gold NPs. The double channel emission of gold nanoclusters with the diameter less than 2 nm was obtained via a p H induced reduction of Au3+. These nanoclusters capped with Au+ on the surface were able to efficiently catalyze the reduction of 4-nitro phenol to 4-aminophenol by Na BH4 in an aqueous environment. As the S-CPL has the sensitive thermally triggered response,the catalytic activity can be controlled by therm-switching. Moreover, the anisotropic Au NPs still showed catalytic activity to reduction of 4-nitrophenol.(4) Amphiphilic block copolymers ligand containing 8-hydroxyquinoline and NIPAM units were prepared via reversible addition-fragmentation chain transfer polymerization(RAFT) and was employed to construct the coordinate micelles. Encapsulation of QDs into the micelles via coordinate interaction can achieve the following purposes: a) Precise control of QDs location in the micellar core or shell; b) Independent double channel emission from the synergistic effects between intrisic emission of QDs and the surface-coordinated emission; c) Based on the trichromatic theory, white-light hybrid micelles were obtained from the special synergy effects of red light emission of QDs, green light emission of surface-coordinated emission and blue light emission of micelles.