Self-assembly Of Au(Ⅰ)-thioiate Coordination Polymers And Their Application In Fabrication Of Au Nanostructures

Metal-organic coordination polymer (CP) nanoassemblies have many excellentproperties, such as, high structure, composition and property tailorability, nanoscaledimension, high surface area, and so on. Thus, CP nanoassemblies show promise foranimpressive number of applications in biological diagnosis, sensing, gas storage, ionexchange and separation, drug release, and catalysis etc. It is well known that uniquephysical properties emerge when nanoscopic dimensions of a material are achieved.Thus, CP nanoassemblies are also expected to hold highly desirable size-andmorphology-dependent optical, electrical and magnetic properties. Thus, scalingdown the size of CP materials to the nanoscale is a critical way for developing newmaterials and improving their performance. In addition, the scope of application of CPmaterials will surely be expanded by rational adjusting their composition andmorphology. More importantly, the reversible polymerization–depolymerizationcharacterization of metal-organic coordination polymers determines their uniqueself-assembly behaviors. They are new kinds of supramolecular materials, and havevery important research significance. Au(Ⅰ)-thiolate CPs are a typical kind of CPmaterials, which have attracted much attention due to their unique aurophilicinteractions. Au(Ⅰ)–thiolates CPs have been reported to self-assemble into precipitateswith unique lamellar structure rapidly. However, the macroscopical dimension ofAu(Ⅰ)–thiolates assemblies not only makes the studies on the assembly mechanismdifficult, but also limits their applications in different areas. To further realize theirapplications in sensing, drug release, preparation of Au nanospecies, and so on, on theone hand, it requires Au(Ⅰ)-thiolate assemblies have nanoscopical dimension, inaddition, characterization methods which can provide molecular-level information forstudying the assembly behaviors and properties are desperately needed. On the other hand, based on the understanding of the assembly mechanism, adopting differentmethods to realize the structural and functional diversification are prerequisite fortheir extended applications.The first chapter of the thesis reviews the developments of CP nanoassemblies,for example, synthetic methods, morphology control, properties and applications, andthe unique aurophilic interactions, the lamellar assemblies and their applications ofAu(Ⅰ)-thiolate CPs. In the end, the design of the thesis is proposed according to theactuality and the problems that remain to be resolved in this area, which is to (i)synthesize Au(Ⅰ)-thiolate nanoassemblies and further understand the molecular-levelstructure and their assembly mechanism;(ii) explore reliable method for adjusting themorphology of Au(Ⅰ)-thiolate nanoassemblies and then lay foundation for extendingtheir applications.The second chapter deals with the methods of reducing the bulk Au(Ⅰ)-MPAlamellar structures to the nanometre scale. UV-vis absorption spectroscopy has beenexplored to monitor the self-assembly process of Au(Ⅰ)-MPA CPs in situ. Bycorrelating the spectral evolutions with nanosized morphological changes, detailedmolecular-level mechanisms of assembly and disassembly have been proposed. Bychoosing water-soluble pH sensitive MPA ligands and trisodiumcitrate as adecomposable pH tuner, nanoassemblies have been successfully achieved and theassembly time has been lengthened to minutes. During their assembly, theAu(Ⅰ)–MPA CPs have underwent a rodthread-rigid-flexible“block-copolymer”-conformation-long-string-structures-coil-structures-thin-lamellar-structures-larger-extended-structures process. Both step-wise and synergetic effects ofthe weak interactions in Au(Ⅰ)–MPA CPs, such as H-bonding, coordination bonding,Au(Ⅰ)–Au(Ⅰ) interactions and static interactions have been found, which elucidates thedriving forces for the unique morphological transformations from strings to lamellarstructures.The third chapter explores chemical exfoliation method to synthesizeAu(Ⅰ)-MPA nanoassemblies with different sizes (dozens to hundreds of nanometers)and shapes successfully. Using the obtained Au(Ⅰ)-MPA nanoassembliesas precursors for fabrication of water soluble gold nanoparticle assemblies has also been studied.The chemical exfoliation process is dominated by manipulating themultipleinteractions in system, such as hydrogen bonding interaction, Au(Ⅰ)–Au(Ⅰ)interaction and Au–S coordinate interaction. By adjusting the amount of exfoliator,nanosheets with tunable thicknesses and nanostrings were achieved. Further, byfabricating Au(Ⅰ)–MPA nanosheets/PEG composite, Au nanoparticle assemblies(average diameters of Au nanoparticles on the edges and in the middle of theassemblies are17.2±8.7nm and7.8±6.0nm respectively) have been achieved byprogressive pyrolysis. Due to the high stability, featuring both Au(0) and Au(Ⅰ)species and the near-field plasmonic coupling and local field enhancement propertiesof the Au nanoparticle assemblies, they could be used in catalysis surface-enhancedRaman scattering areas.The fourth chapter explore water-in-oil microemulsion method to synthesizeAu(Ⅰ)-MPA assemblies (hundreds of nanometers) with diverse regular morphologies,and the application of these nanoassemblies in preparation of Au particle with largesize and photoluminescent Au clusters have also been illustrated. The microemulsionnot only has constraint ad direction effects on the assembly of Au(Ⅰ)–MPA CPs, butalso could further slow down the assembly speed. In this way, Au(Ⅰ)-MPA assemblieswith regular shape can be obtained in a well controllable way. The influences of the wvalues of microemulsion and the pH values of the reactants on the morphology of theassemblies have been studied. Obviously, both the coalescence between droplets andthe electrostatic interaction between MPA ligands determines the shape of the finalproducts. Au particles with diameters of520nm and250nm, red (QY:0.3%) andblue (QY:16.4%) photoluminescent Au clusters were obtained using Au(Ⅰ)–MPAquasi-square nanosheets, nanostrings and nanochips as precursors under solvothermalconditions. Due to the highly sensitive localized surface plasmon resonance of largesized Au particles and the photoluminescence of Au clusters, they could be applied insensing and bioimaging areas.To sum up, a lot of fundamental work on understanding the assembly mechanismof CPs, preparation of Au(Ⅰ)-MPA nanoassemblies with different size and shape, and fabrication of Au nanospecies has been done and it lays foundation for the extensionof applications of Au(Ⅰ)-MPA CPs.