Interfacial Assembly And Properties Of Metal And Pyridine - Containing Multidentate Ligand Composite Polymer Materials

Studies of the molecular aggregated materials focus on design, characterization of novel supramolecular compounds as well as on the function and applications in molecular level, which is different from those of the traditional molecular chemistry where in more attention is paid on building molecules from atoms. Molecular assembly has been studied by a lot of researchers from a wide range of fields. Due to its function-oriented, we can choose the proper molecular and design the process particularly according to the application prospects.In this thesis, multi-dentate ligands containing pyridine substituents with good photochemical properties were selected to build the molecular assembly materials through interfacial coordination reaction. What’s more, different metals and nano titanium dioxide were also involved in this investigation in order to study hybrid materials. Compositions, structure, physicochemical and catalytic properties of the as-prepared materials were investigated.In the first part, metal-bisterpyridine coordination polymers (CPs) have been synthesized at the air-water interface through an interfacial coordination reaction of metal ions (Zn2+/Fe2+) with bidentate ligand of4,4’"-(1,4-phenylene) bis (2,2’:6’2"-terpyridine)(PBTerpy). Surface pressure-area isotherms indicated that the average molecular area of PBTerpy was about0.8nm2on the pure water surface, which slightly increased to about1nm on the inorganic salt subphase surfaces due to the formation of Zn(Fe)-PBTerpy CPs. Monolayers of the Zn(Fe)-PBTerpy CPs were deposited on the quartz, Si and indium tin oxide (ITO) sub-strate surfaces by the Langmuir-Blodgett (LB) method. The as-prepared LB films were characterized by using UV-vis absorption and fluorescence spectroscopy, X-ray photoelectron spectroscopy, as well as by using scanning electron microscope and atomic force microscope. The pure PBTerpy ligand and its LB films showed a broad fluorescent emission at about350-370nm. This emission red shifted to about380-410nm in the LB films of Zn(Fe)-PBTerpy CPs. Time-resolved fluorescent spectra revealed that the emission lifetime was about1.2-2.4ns for the pure PBTerpy ligand in the dilute methanol solution and its LB films, while it was about5.0ns in the LB film of Fe-PBTerpy CPs and20.6ns in the LB film of Zn-PBTerpy CPs. A couple of reversible redox wave was recorded and centered at about-0.53V (vs Ag/AgCl) for the ITO electrode covered by the LB film of Fe-PBTerpy CPs, which was designated to one electron transfer process between the CPs of Fe(II)-PBTerpy and Fe(III)-PBTerpy. Since the PBTerpy can coordinate with lots of transition metal ions, we suggest that the present method may be used to prepare new optically and electrically active organic-inorganic composite materials.In the second part, triad hybrid multilayers containing the light sensitizers of zinc tetrapyridylporphyrin (ZnTPyP) and pyridine-functionalized TiO2(TiO2-Py) nanoparticles were constructed on substrate surfaces with the use of Pd(Ⅱ) ions as the connectors using the layer-by-layer (LBL) method. The assembly process was monitored using ultraviolet-visible (UV-vis) absorption and X-ray photoelectron spectra as well as scanning electron microscopy and atomic force microscopy. The content of the pyridine substituents in the TiO2-Py nanocomposites was about2%(w/w). The Soret absorption band of ZnTPyP was24nm red-shifted in the hybrid multilayers due to a strong intermolecular electronic coupling interaction among porphyrin macrocycles or porphyrin macrocycle/TiO2-Py nanoparticles. The average surface density of each ZnTPyP layer was about1.4x10-10mol/cm2. Aggregation of the small TiO2-Py nanoparticles to larger domains with sizes up to hundreds of nanometers occurred in the hybrid multilayers; however, such an aggregation behavior was weaker than that in the solutions. The quartz substrate modified with the as-prepared Pd/ZnTPyP/Pd/TiO2-Py triad hybrid multilayers was used as a heterogeneous photocatalyst for the degradation of methyl orange (MO) under irradiation (λ>420nm) at room temperature with a catalytic efficiency of about1.3×10-3MO/ZnTPyP-s. It is suggested that the present heterogeneous catalyst has the advantages of facile separation, high stability, structural controllability on the molecular and nanoscale level, and good recyclability.