Synthèse, caractérisation et photo-réactivité de polyoxométallates inorganiques et hybrides organique-inorganique

Les polyoxométallates (POMs) sont des oxydes moléculaires anioniques de métaux de transition à haut degré d oxydation (exclusivement Mo et W dans notre étude) et présentent une grande diversité de composition chimique, de structure et de dimensionnalité. A l état solide, les POMs développent des propriétés optiques photo-induites remarquables qui couplent la photo-génération de paires excitoniques dans le POM à des transferts électroniques, et parfois atomiques, à l interface POM/contre-cation. Dans cette thèse, les transferts électroniques photo-activés des POMs ont été mis à profit pour élaborer de nouveaux matériaux hybrides organique-inorganique photochromes à l état solide ainsi que de nouveaux photocatalyseurs plasmoniques dans le visible. Dans la première partie de ce travail, une nouvelle famille de matériaux photochromes a été synthétisée en combinant des POMs avec des cations sulfonium. Les propriétés optiques de ces systèmes hybrides ont été caractérisées et un nouveau mécanisme de photochromisme a été proposé. Parallèlement à ces travaux, l assemblage de POMs avec des molécules organiques elles-mêmes photo-actives (spiropyrane, spironaphtoxazine) a ouvert la voie à une seconde famille de matériaux aux propriétés photochromiques exaltées. La deuxième partie de cette thèse est consacrée à l étude de la nanostructure Ag@Ag2Mo3O10 2H2O obtenue selon une nouvelle méthode de photo-déposition tout solide à partir du molybdate d argent Ag2Mo3O10 2H2O, les nanofils Ag2Mo3O10 2H2O étant obtenus par une voie de synthèse inédite en conditions douces. La nanostructure Ag@Ag2Mo3O10 2H2O s avère être un photocatalyseur plasmonique efficace sous lumière visible.Polyoxometalates (POMs) are anionic molecular oxide building blocks of high oxidation state transition metals (only Mo and W in our study) and have a wide variety of chemical composition, structure and dimensionality. In the solid state, POMs develop remarkable photo-induced optical properties coupling the photo-generation of excitonic pairs in the POM with electronic, and sometimes atomic, transfers at the POM/counter-cation interface. In this thesis, the photo-activated electronic transfers of the POMs have been used to develop new photochromic organic-inorganic hybrid materials in the solid state as well as new plasmonic photocatalysts in the visible. In the first part of this work, a new family of photochromic materials was synthesized combining POMs with sulfonium cations. The optical properties of these hybrid systems have been characterized and a new mechanism of photochromism was proposed. Alongside this work, the assembly of POMs with photoactive organic molecules (spiropyran and spironaphthoxazine) constitutes a second family of materials with exalted photochromic properties. The second part of this thesis is devoted to the study of the nanostructure Ag@Ag2Mo3O10 2H2O obtained by a new "all solid state" photo-deposition method from the silver molybdate Ag2Mo3O10 2H2O obtained by an unprecedented route under mild conditions. The Ag@Ag2Mo3O10 2H2O nanostructure appears to be an efficient visible-light-driven plasmonic photocatalyst.NANTES-BU Sciences (441092104) / SudocSudocFranceF

Plasmonic properties of an Ag@Ag 2 Mo 2 O 7 hybrid nanostructure easily designed by solid-state photodeposition from very thin Ag 2 Mo 2 O 7 nanowires

International audienceA new Ag@m-Ag2Mo2O7 plasmonic hybrid nanostructure was designed by an easy two-step synthesis method. Firstly, very thin photosensitive monoclinic m-Ag2Mo2O7 nanowires (NWs) were synthesized under ambient pressure and at low temperature by using Ag2Mo3O10·2H2O NWs as a pre-nanostucturated starting material. This innovative soft chemistry route offers some precise control over the purity, the structure and the nanostructuration of the m-Ag2Mo2O7 NWs that exhibit a very thin diameter of around 100 nm and a superior specific surface area compared to previously reported synthesis methods. Secondly, the plasmonic hybrid nanostructure Ag@m-Ag2Mo2O7 was easily in situ obtained via an all solid-state photodeposition method, by irradiating the m-Ag2Mo2O7 NWs under low energy and low-power UV-light. The composition, morphology and plasmonic properties of the nanocomposite were investigated by a combination of energy-dispersive X-ray spectroscopy, high-resolution scanning transmission electron microscopy, X-ray photoelectron spectroscopy and Auger spectroscopy, and near-infrared, Raman and UV-vis spectroscopies as well as spatially-resolved electron energy-loss spectroscopy. A plausible mechanism explaining the formation of the nano-heterostructure under irradiation was also discussed. The Ag@m-Ag2Mo2O7 nanostructure manifests interesting plasmonic properties particularly high surface-enhanced Raman scattering (SERS) sensitivity probed using 2,2′-bipyridine

Introductory Note by the Editors-in-Chief

International audiencePolyoxometalates covalently linked to one or two spiropyran entities have been isolated. These organic-inorganic hybrids exhibit multi-electrochromic and photochromic properties

Photochromic Properties of Polyoxotungstates with Grafted Spiropyran Molecules

International audienceThe first systems associating in a single molecule polyoxotungstates (POTs) and photochromic organic groups have been elaborated. Using the (TBA)4[PW11O39{Sn(C6H4I)}] precursor, two hybrid organic-inorganic species where a spiropyran derivative (SP) has been covalently grafted onto a {PW11Sn} fragment via a Sonogashira coupling have been successfully obtained. Alternatively, a complex containing a silicotungstate {PW11Si2} unit connected to two spiropyran entities has been characterized. The purity of these species has been assessed using several techniques, including 1H and 31P NMR spectroscopy, mass spectrometry, and electrochemical measurements. The optical properties of the hybrid materials have been investigated both in solution and in the solid state. These studies reveal that the grafting of SPs onto POTs does not significantly alter the photochromic behavior of the organic chromophore in solution. In contrast, these novel hybrid SP-POT materials display highly effective solid-state photochromism from neutral SP molecules initially nonphotochromic in the crystalline state. The photoresponses of the SP-POT systems in the solid state strongly depend on the nature and the number of grafted SP groups

Design and optical investigations of a spironaphthoxazine/polyoxometalate/spiropyran triad

International audienceThe richness of the optical properties of covalent polyoxometalate/organic chromophores compounds is reported

Photochromic Properties of Polyoxotungstates with Grafted Spiropyran Molecules

The first systems associating in a single molecule polyoxotungstates (POTs) and photochromic organic groups have been elaborated. Using the (TBA)₄­[PW₁₁O₃₉­{Sn­(C₆H₄I)}] precursor, two hybrid organic–inorganic species where a spiropyran derivative (SP) has been covalently grafted onto a {PW₁₁Sn} fragment via a Sonogashira coupling have been successfully obtained. Alternatively, a complex containing a silicotungstate {PW₁₁Si₂} unit connected to two spiropyran entities has been characterized. The purity of these species has been assessed using several techniques, including ¹H and ³¹P NMR spectroscopy, mass spectrometry, and electrochemical measurements. The optical properties of the hybrid materials have been investigated both in solution and in the solid state. These studies reveal that the grafting of SPs onto POTs does not significantly alter the photochromic behavior of the organic chromophore in solution. In contrast, these novel hybrid SP–POT materials display highly effective solid-state photochromism from neutral SP molecules initially nonphotochromic in the crystalline state. The photoresponses of the SP–POT systems in the solid state strongly depend on the nature and the number of grafted SP groups

Novel Soft-Chemistry Route of Ag₂Mo₃O₁₀·2H₂O Nanowires and in Situ Photogeneration of a Ag@Ag₂Mo₃O₁₀·2H₂O Plasmonic Heterostructure

Ultrathin Ag₂Mo₃O₁₀·2H₂O nanowires (NWs) were synthesized by soft chemistry under atmospheric pressure from a hybrid organic–inorganic polyoxometalate (CH₃NH₃)₂[Mo₇O₂₂] and characterized by powder X-ray diffraction, DSC/TGA analyses, FT-IR and FT-Raman spectroscopies, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Their diameters are a few tens of nanometers and hence much thinner than that found for silver molybdates commonly obtained under hydrothermal conditions. The optical properties of Ag₂Mo₃O₁₀·2H₂O NWs before and after UV irradiation were investigated by UV–vis–NIR diffuse reflectance spectroscopy revealing, in addition to photoreduction of Mo⁶⁺ to Mo⁵⁺ cations, in situ photogeneration of well-dispersed silver Ag⁰ nanoparticles on the surface of the NWs. The resulting Ag@Ag₂Mo₃O₁₀·2H₂O heterostructure was confirmed by electron energy-loss spectroscopy (EELS), X-ray photoelectron spectroscopy (XPS), and Auger spectroscopy. Concomitant reduction of Mo⁶⁺ and Ag⁺ cations under UV excitation was discussed on the basis of electronic band structure calculations. The Ag@Ag₂Mo₃O₁₀·2H₂O nanocomposite is an efficient visible-light-driven plasmonic photocatalyst for degradation of Rhodamine B dye in aqueous solution

Photochromic Properties of Polyoxotungstates with Grafted Spiropyran Molecules

The first systems associating in a single molecule polyoxotungstates (POTs) and photochromic organic groups have been elaborated. Using the (TBA)₄­[PW₁₁O₃₉­{Sn­(C₆H₄I)}] precursor, two hybrid organic–inorganic species where a spiropyran derivative (SP) has been covalently grafted onto a {PW₁₁Sn} fragment via a Sonogashira coupling have been successfully obtained. Alternatively, a complex containing a silicotungstate {PW₁₁Si₂} unit connected to two spiropyran entities has been characterized. The purity of these species has been assessed using several techniques, including ¹H and ³¹P NMR spectroscopy, mass spectrometry, and electrochemical measurements. The optical properties of the hybrid materials have been investigated both in solution and in the solid state. These studies reveal that the grafting of SPs onto POTs does not significantly alter the photochromic behavior of the organic chromophore in solution. In contrast, these novel hybrid SP–POT materials display highly effective solid-state photochromism from neutral SP molecules initially nonphotochromic in the crystalline state. The photoresponses of the SP–POT systems in the solid state strongly depend on the nature and the number of grafted SP groups

VR as a tool for specification of functional requirement in construction of hospital facilities

This paper investigates how virtual reality (VR) can facilitate the planning of new hospital premises from an end-user perspective and whether VR can minimize the risk of costly reconstructions close after commissioning. Currently, review of hospital premises is done in 2D based blueprints and 3D models. These blueprints and models do not always provide sufficient understanding on the hospital staff’s part. VR has been developed by suppliers to counteract this problem and to function as a design review tool for the end-users. VR is mainly used in the design phase of the building process, whereas it acts as a complementary design tool during the later phases of the building process, when the end-user participation is less tangible. Due to VR not being an established tool for all parties involved in the building process, it has consequently led to difficulties for the hospital in terms of understanding the value of said technique and knowing what set of requirements that should be taken into consideration when implementing VR into the building project. The results in this paper have shown that VR is a better tool during the design process than other available review tools. This enhanced understanding is not only limited to the end-users, but the suppliers as well have shown a better understanding of what they offer to their hospital clients. The results also show that the value of VR mainly is apparent during the design phase and less evident during the later phases of the building process due to the technical limitations VR currently faces