Light-Controlled Self-Assembly Of Anthracene Modified Surfactant/Polyoxometalate Complexes

Polyoxometalates (POMs) are a kind of molecularly defined, nanoscale inorganicclusters with rich functionality. They show excellent properties in catalysis, optics,electrochemistry, magnetism and so on. So they can be used as a kind of inorganicfunctional building blocks. However, POMs usually exist as powder or inorganiccrystals, which are detrimental to their functional implementation. It is essential tomodify POMs with more responsive and functional constituent, which have a hugeapplication value to realize the various functionality of polyoxometalates. Moreover, thesoft matter systems are introduced into polyoxometalates, which broadens the path ofdevelopment of supramolecular assembly.There are mainly two ways to modify organic group on polyoxometalates: a) thefirst one is the covalent modification of organic components to the POMs. b) the secondone is that using surfactants to encapsulate the POMs. For molecular assembly, a simpleapproach currently used is to replace the counterions of POMs by organic cations.Because of the multi-charges of POMs, we use the method of ion replacement to changethe organic part which can improve the solubility of complex and the stability of theclusters.Organic modified polyoxometalate is an amphiphilic supramolecular complexes, it has hydrophilic clusters and the hydrophobic organic group. By adjusting theenvironment of self-assembly (solvent, temperature, concentration, etc.) and replacingthe organic constituent, it can achieve to control the assemble behavior. In thisdissertation, we firstly designed and synthesized supramolecular complexes based onstimulus-response constituent, by adjusting the light, solvents, and redox conditions torealize the controllable aggregation.First, in order to get new assembly, we designed and synthesized surfactant withanthracene. Then we used single-phase co-precipitation method to get the(anthracene-double)4-PMo11V this supramolecular complexes, through ion replacementwith the Keggin-type polyoxometalate H4PMo11V.1H NMR spectra and IR spectraconfirm the presence of the strong electrostatic interaction between cationic surfactantand POMs. Elemental analysis (EA) data confirms the molecular composition.Second, we adjusted the mixed solvent to control the dynamic self-assembly. Inacetonitrile and n-propanol mixed solvent, we got spherical aggregates with roughsurface; in THF and methanol mixed solvent, we got nanosheet aggregates. But in THFand n-propanol or THF and n-butanol mixed solvent, we got the hollow micro-sphere.The size of the aggregates is between700nm and1μm. The XRD and TEM resultsimply that the assembles are arranged by lamellar structure in solution. The anthracenecan form dimer after UV irradiation, so we can use this property to change themorphology. After UV irradiation in THF/n-butanol mixed solvent, the morphologychanged from hollow micro-sphere to solid micro-sphere. In this process, there isenergy transfer between polyoxometalate and anthracene, which can realize thefluorescence quenching.Third, because solvent evaporation can induce self-assembly, we successfullytransferred this amphiphilic molecules from the organic phase to water phase. We useDLS, SEM, TEM and XRD to characterize the assembly of(anthracene-double)4-PMo11V in water phase. After UV irradiation, anthracene occurs photo-crosslinking, which can improve the stability of aggregates in water. In addition,we can achieve in-situ reduction of Ag nanoparticles by using stable vesicularaggregates as a tamplate through its photochromic properties. This novelsupramolecular structure and light-controlled assemble behavior provide a new modelsystem for the development of stimuli-responsive organic-inorganic hybrid materials.In conclusion, we focus on the study of dynamic self-assembly of supramolecularcomplex with stimulus-response constituent, and realize different modulation strategy,such as the light, solvent environment and redox. We believe that these findings willprovide a new model system for the development of stimuli-responsiveorganic-inorganic hybrid materials.