Recent Advances in Polyoxometalate-Catalyzed Reactions

Control of spontaneously emitted light lies at the heart of quantum optics. It is essential for diverse applications ranging from miniature lasers and light-emitting diodes, to single-photon sources for quantum information, and to solar energy harvesting. To explore such new quantum optics applications, a suitably tailored dielectric environment is required in which the vacuum fluctuations that control spontaneous emission can be manipulated. Photonic crystals provide such an environment: they strongly modify the vacuum fluctuations, causing the decay of emitted light to be accelerated or slowed down, to reveal unusual statistics, or to be completely inhibited in the ideal case of a photonic bandgap. Here we study spontaneous emission from semiconductor quantum dots embedded in inverse opal photonic crystals. We show that the spectral distribution and time-dependent decay of light emitted from excitons confined in the quantum dots are controlled by the host photonic crystal. Modified emission is observed over large frequency bandwidths of 10%, orders of magnitude larger than reported for resonant optical microcavities. Both inhibited and enhanced decay rates are observed depending on the optical emission frequency, and they are controlled by the crystals’ lattice parameter. Our experimental results provide a basis for all-solid-state dynamic control
of optical quantum systems.

Controlling the dynamics of spontaneous emission from quantum dots by photonic crystals

Materials fabrication with nanoscale structural precision based on bottom-up-type self-assembly has become more important in various current disciplines in chemistry including materials chemistry, ...

Layer-by-layer Nanoarchitectonics: Invention, Innovation, and Evolution

Supramolecular Amphiphiles Based on Host-Guest Molecular Recognition Motifs.

Polyoxometalates (POMs) have remarkable properties and a great deal of potential to meet contemporary societal demands regarding health, environment, energy and information technologies. However, implementation of POMs in various functional architectures, devices or materials requires a processing step. Most developments have considered the exchange of POM counterions in an electrostatically driven approach: immobilization of POMs on electrodes and other surfaces including oxides, embedding in polymers, incorporation into Layer-by-Layer assemblies or Langmuir–Blodgett films and hierarchical self-assembly of surfactant-encapsulated POMs have thus been thoroughly investigated. Meanwhile, the field of organic–inorganic POM hybrids has expanded and offers the opportunity to explore the covalent approach for the organization or immobilization of POMs. In this critical review, we focus on the use of POM hybrids in selected fields of applications such as catalysis, energy conversion and molecular nanosciences and we endeavor to discuss the impact of the covalent approach compared to the electrostatic one. The synthesis of organic–inorganic POM hybrids starting from bare POMs, that is the direct functionalization of POMs, is well documented and reliable and efficient synthetic procedures are available. However, as the complexity of the targeted functional system increases a multi-step strategy relying on the post-functionalization of preformed hybrid POM platforms could prove more appealing. In the second part of this review, we thus survey the synthetic methodologies of post-functionalization of POMs and critically discuss the opportunities it offers compared to direct functionalization.

Functionalization and post-functionalization: a step towards polyoxometalate-based materials

Hybrid polyoxometalate-porphyrin copolymeric films are obtained by the electro-oxidation of zinc octaethylporphyrin (ZnOEP) and zinc 5,15-dipyridinium octaethylporphyrin (5,15-ZnOEP(py)22+) in the presence of the polyoxometalate [MnMo6O18{(OCH2)3CNHCO(4-C5H4N)}2]3− (Py-POM-Py). These films allow the photocatalytic reduction of AgI2SO4 under visible irradiation in air in the presence of propan-2-ol at the 2D interface between water and the copolymeric films. The formation of metallic Ag0 nanowires and triangular nanosheets is observed.

Synthesis and photocatalytic properties of mixed polyoxometalate-porphyrin copolymers obtained from Anderson-type polyoxomolybdates.

Fluidization of a Dipalmitoyl Phosphatidylcholine Monolayer by Fluorocarbon Gases: Potential Use in Lung Surfactant Therapy

Monolayers of fluorinated amphiphiles present specific structure and properties, due to differences in chain stiffness and molecular interactions between fluorinated and hydrogenated amphiphiles. The combined hydrophobicity and lipophobicity of fluorinated chains result in lateral and vertical micro phase separation when fluorinated and hydrogenated amphiphiles are mixed. Monolayers of fluorinated amphiphiles have potential applications in materials and biological sciences, including for two-dimensional protein crystallization and microelectronics.

Monolayers made from fluorinated amphiphiles

Self-assemblies of a calix[6]arene (1) functionalized at the small rim by three imidazolyl arms and at the large rim by three hydrophilic sulfonato groups have been studied in water. Transmission electron microscopy, atomic force microscopy, and in situ dynamic light scattering showed that 1 forms multilamellar vesicles at a concentration equal to or higher than 10-4 M. At pH 7.8 and 10-4 M, the multilamellar vesicles present a relatively large polydispersity (50−250 nm in diameter). However, after sonication unilamellar vesicles of much lower polydispersity and smaller size are obtained. The impact of the pH and the presence of Ag+ ions have also been investigated. Whereas increasing the pH led to the formation of giant vesicles (450 nm), monodisperse vesicules of 50 nm were obtained at a pH (6.5) that is only slightly higher than the pKa of the tris(imidazole) core of 1. Most interestingly, in the presence of silver ions, micelles (2.5 nm large) were obtained instead of vesicles. These observations are ...

Architecture-controlled "SMART" Calix[6]arene self-assemblies in aqueous solution.

We report the first direct evidence for the formation of circular surface micelles (hemimicelles) on the surface of water. These highly monodisperse 30 nm hemimicelles, made from a semifluorinated alkane deposited as a Langmuir monolayer, form organized hexagonal arrays as determined by small-angle X-ray diffraction conducted directly on the water surface at grazing incidence.

Michel Goldmann

Papers

Synthesis and photocatalytic properties of mixed polyoxometalate-porphyrin copolymers obtained from Anderson-type polyoxomolybdates.

Fluidization of a Dipalmitoyl Phosphatidylcholine Monolayer by Fluorocarbon Gases: Potential Use in Lung Surfactant Therapy

Monolayers made from fluorinated amphiphiles

Architecture-controlled "SMART" Calix[6]arene self-assemblies in aqueous solution.

Direct Evidence for Highly Organized Networks of Circular Surface Micelles of Surfactant at the Air−Water Interface