Polyoxometalates For The Building Blocks Of Ultra-thin Films: From Structure To Assembly To The Function To Build

The design and attainment of functional molecular materials have been a main challenge for scientists in now world when science and technology competition is becoming more and more drastic. Polyoxometalates (POMs) have been found to be extremely versatile inorganic building blocks for the construction of novel functional materials owing to their defined structure and predominant physical properties, in particular electrical, magnetic, and optical properties. After POMs are introduces into nanocomposite films by virtue of intermolecular weak acting force, the cooperative action from inorganic and organic components can induce and bring novel functional characteristics. It can create more chances for the application of this kind of inorganic building blocks in the fields of materials. Layer-by-layer (LbL) self-assembly technique has been proved to be a powerful and versatile means for assembling multicomposite supramolecular structures. Many inorganic components have been incorporated into polymers, which could be applied in chemical sensors, modified electrodes and photoelectronics. In this thesis, author carried out a series of research in multilayers based on POMs and their properties, and some constructive and helpful results were obtained. All the results are summarized as follows: 1. Firstly, we have demonstrated that a convenient method of adsorption-deposition can be applied to in situ synthesize size-controlled Ag3PW12O40 nanoparticles. And sequential absorption of polyelectrolyte built the multilayered structure. The key point of this approach is that acidity of POMs can control the released amount of Ag+ complexed with –COO- groups of PAA and in turn control the size of nanoparticles. At the same time the polyelectrolyte, which acts as the stabilizer to stabilize silver ions, contributes to in situ synthesis of POMs nanoparticles. 2. Novel photo- and thermochromic inorganic-organic multilayers composed of POMs and PEI have been prepared by LbL self-assembly method. Irradiated with ultraviolet light or heated, the transparent films changed from colorless to blue. Moreover, the blue films showed good reversibility of photo- and thermochromic, and could recover the colorless state gradually in air where oxygen plays an important role in the bleaching process. On account of the ESR and XPS results, parts of W6+ in multilayers were reduced to W5+ which exhibited characteristic blue, a possible photo- or thermochromic mechanism can be speculated. 3. Ultrathin multilayer films containing a lacunary Dawson type polyoxometalates cluster K17[Ln(P2Mo17O61)2] (Ln = Eu, Tb) and PAH have been prepared by LbL method. The photoluminescent behavior of films at room temperature was investigated to show the Ln3+ characteristic emission pattern. Additionally, the electrochemical behavior of multilayer films was studied and the growth of multilayer films can be observed.