Preparation And Properties Of Fluorescent Microtubes Based On Polyoxometalates

In this thesis, by selecting the classical Keggin-type polyoxometalate （POM） as asubstrate, three kinds of POM microtubes have been synthesezed through a two-stepreaction mechanism, i.e., organic dye F-doped POM microtubes, a series of lanthanideions doped12-tungstosilicate microtubes and ADM-doped POM microtubes.Synthesis conditions, growth mechanism and fuorescent properties of the POMmicrotubes are discussed systematically.1. Fluorescein sodium （FS） is a common organic fluorescent dye in the yellowgreen region, and has numerous applications in optoelectronic devices, serologicidentification, immunology, and so on. FS can be introduced into the POM microtubes,so that the POM microtubes may show tunable photoluminescence. Based on ourprevious work, we systematically study the preparation and fluorescent properties ofthe Keggin-type α-SiMW₁₁-F （M=WVI, MoVIand VV） microtubes doped withfluorescein dye. Comparative studies have been carried out on fluorescent propertiesof the three SiMW₁₁-F microtubes and fluorescein sodium. These fluorescent hybridmicrotubes exhibit luminescent emission properties which are different from those offluorescein sodium in the blue spectral region. These results indicate that differentluminescence centers may be formed in the hybrid microtubes. The SiW₁₂-F andSiMoW₁₁-F microtubes show more similar fluorescent properties than the SiVW₁₁-Fmicrotubes, due to the differences in ionic radius and oxidation state between W/Moand V. Furthermore, the three polyoxometalate components in the microtubes exhibitan inhibiting effect on photobleaching of fluorescence dye FS.2. POM-based lanthanide compounds display appealing physicochemicalproperties, including luminescence, single-molecule magnetism and Lewis acidcatalytic activity. The lanthanide cations can be introduced into the POM microtubesthrough replacing part of K+ions in the microtubes, so that the POM microtubes areendowed with the properties of lanthanide cations. So a series of lanthanide-dopedpolyoxometalate microtubes, Ln-SiW₁₂（Ln=Eu, Tb, Dy, Nd and Yb）, have beensynthesized, and their PL properties have been studied.As is known,8-hydroxyquinoline （HQ） and its derivatives are effective chelatingligands, suitable for complexation of trivalent lanthanide ions. Furthermore,coordination complexes of HQ are often strongly luminescent emission either in solution or in solid phase, so it is a good candidate for preparation of Ln-basedluminescent materials. Based on this consideration, we have further explored apost-synthesis method to obtain LnQ-SiW₁₂（Ln=Dy（III）, Nd（III）, Yb（III）） microtubes,which have a NIR emitting property generating from LnQ. It is noted that, in thiswork, a significant difference from our previous reports is that12-tungstosilic acid(H4SiW₁₂O₄₀) is used instead of mono-lacunary POM, potassium11-tungstosilicate(K8SiW₁₁O39). Thus a species transformation from the11-series to12-seriestungstosilicate was not necessary.3. Doxorubicin（ADM） has been used for over50years to treat a variety of cancers.Doxorubicin is a compound that has attracted a great deal of research activity becauseof its utility as a pharmaceutical and its reactivity under a variety of conditions. Inaddition, heteropolyanions [SiWl2O₄₀]^4-have stronger antiviral activity. Therefore, itshould be interesting to explore the ADM-doped tungstosilicate (SiW₁₂-ADM)microtubes that endow di-functions of ADM and POM components. We found thatADM molecules not only can be successfully doped into the microtubes, but alsoremain good fluorescent propertie. Furthermore, fluorescent properties of theSiW₁₂-ADM microtubes keep well upon exposure to H2S or NH3gases. These resultsindicate that microtubes based on polyoxometalate and ADM hold potential inbioprobes.The as-prepared POM tubular materials may display potential applicationsin wavelength converter, display, laser materials, and fluorescent probe, due tocombination of the physicochemical properties of POMs and the dopants.