Synthesis And Self-Assembly Properties Of Organic-Inorganic Hybrid Molecules: Oxadiazole-Containing Cyclotriphosphazene

The spontaneous self-assembly of small molecules to form nanostructures, such as spheres, tubes, rods, wires, belts, has evolved as an attractive strategy for fabricating materials with tunable physical and chemical properties via control of their composition, size, and shape. Such materials possess unique physical and chemical properties and potential applications in electronic and optoelectronic nanodevices. Hexachlorocyclotri-phosphazene is an important intermediate in phosphazene chemistry. The most striking characteristic of this type of compound is its associated synthetic versatility, which enables the introduction of almost any substitute group R at phosphorus and allows properties to be tailored by the choice of appropriate functional groups. In recent years, the derivatives of cyclotriphosphazene have also received extensive attention in preparation of nano-materials, such as phosphazene nanotubes, phosphazene microspheres.In this thesis, nine cyclotriphosphazene derivatives with oxadiazole groups (5-phenyl-1,3,4-oxadiazole,5-(phenylethynyl)-1,3,4-oxadiazole,5-(4-pyridyl)-1,3,4-oxadiazole) and different substituents number (two, four, six) were synthesized by nucleophilic substitution of hexachlorocyclotriphosphazene. The molecular structures of these compounds were characterized by 1H,13C,31P-NMR and mass spectrometry. Herein, the 1,3,4-oxadiazole groups were incorporated in the molecules in view of their excellent ability to undergo efficientπ-πstacking. In this paper, we studied the capability of cyclotriphosphazene oxadiazole derivatives forming nano-and micromaterials viaπ-πself-assembly and the properties of the resulted materials.Via two simple solution processes, single-crystal nano-and microbelts of hexakis-(4-(5-phenyl-1,3,4-oxazodiazol-2-yl)-phenoxy)cyclotriphosphazene (HPCP) have been prepared by exploiting the strongπ-πinteractions between neighboring HPCP molecules as the driving force. By tuning the solubility of HPCP by varying the solvent and the volume ratio of solvents, the thickness and the length of belts gradually changed from tens to 500 nm and tens of micrometers to several millimeters, respectively. A growth mechanism for the 1-D self-assembly has been proposed. Crystal structure analysis supports that the contact between the oxadiazole groups of the phosphazene backbone forms effectiveπ-πintermolecular linking for 1-D crystal growth. Current-voltage (Ⅰ-Ⅴ) measurement of single nano- and microbelts shows that these new nano- and microbelts have little conductivity. The conductivity of microbelts is ca.6.0×10-5 Scm-1, a value belonging to the scope of the semiconductor. These new nano- and microbelts also demonstrate dramatic emission.Hexakis-(4-(5-styryl-1,3,4-oxazodiazol-2-yl)-phenoxy)-cyclotriphosphazene (HSCP) could self-assemble into nanobelts and micro flower-like structures via simple solvent exchange process by exploiting theπ-πinteractions between neighboring HSCP molecules as the driving force. Microscopic investigations provided clear evidence for the different superstructures obtained by tuning the solubility of HSCP via varying the volume ratio of solvents. The UV-Vis, FTIR,1HNMR, FSEM and Fluorescence microscopy studies show that HSCP capable of undergoing [2+2] photodimerization both in solution and solid state. And 1HNMR analysis evidences that the result photoreaction products of the as prepared nanobelts different from the solution, which have a better stereochemistry control. These new superstructure materials include nanobelts, and flower-like particles also demonstrate dramatically emission before and after photo-irradiation. The resulted superstructures can be retained during the photoreaction process and obtained insoluble cross-linking polymer network materials. A growth mechanism for the 1-D self-assembly and photoreaction has also been proposed. In addition, HSCP can self-assembly from different solvents such as DMF, THF, dioxane, chloroform and toluene by the solvent evaporation method on glass substrate, obtained microspheres, film, and spiral disk structures.The properties of hexakis-(4-(5-(4-pyridyl)-1,3,4-oxadiazole-yl)phenoxy)cyclotripho-sphazene (bwez) were preliminary studied. Its fluorescence changes in solution were unlike the above two compounds, showing the dissociation of aggregate molecules similar to hemoglobin, indicating that the pyridyl oxadiazole cyclotriphosphazene derivative has a stronger interaction between molecules. Also, one-dimensional materials of Hbwez can be self-assembled through the solvent exchange method.The self-assembly properties of two asymmetric cyclotriphosphazene oxadiazole derivatives,1,1-catechol-3,3,5,5-tetra(4-(5-phenyl-1,3,4-oxadiazole-2-yl)-phenoxy)cycl-otriphosphazene (TPCP) and 1,1,3,3-bis-catechol-5,5-bis(4-(5-phenyl-1,3,4-oxadiazole-2-yl)-phenoxy)cyclotriphosphazene (DPCP) were investigated. The results show that, TPCP self-assembled into elliptical sheet crystals rather than one-dimensional material. The DPCP mainly formed one-dimensional self-assembled materials, and the resulting fibers have good flexibility.