Game of Crowns: Na+ Is Coming! Red NIR-Emissive Hybrid Liquid Crystals Containing Discotic Crown Ethers and Na2Mo6X8iCl6 (Xi = Cl or Br).

Molecular or supramolecular materials that can self-organize into columns such as discotic liquid crystals are of interest for several applications in the field of optoelectronics. We show in this work that red near-infrared (NIR)-emissive metal cluster compounds of general formula Na2Mo6X8iCl6 (Xi = Cl or Br) can be readily complexed with discotic liquid crystals containing a crown ether. Three cavity sizes have been tested with crown ethers bearing 4, 5, or 6 oxygen atoms. In all cases, 1:1 complexes were formed, thanks to the well-known supramolecular interactions existing between the Na+ cations of the metal cluster salt and the crown ether derivatives. All obtained hybrids are homogeneous, emit in the red NIR region, and show liquid crystalline properties on a wider temperature range than their precursors. Charge transport properties have been investigated by using a space charge limited current device. Obtained results demonstrate that metal cluster compounds can enhance the charge carrier mobility by 5 orders of magnitude compared to the native discotic organic ligands. Considering that the presented organic crown ether derivatives are not the best candidates to design optoelectronic devices because of their inherently low conductivity, but that similar compounds were developed to design proton conductive porous framework, our results open promising perspectives for the use of metal cluster compounds in devices dedicated to such a field.

Flexible and Transparent Luminescent Cellulose-Transition Metal Cluster Composites.

Red-NIR luminescent polymers are principally obtained from petroleum-based derivatives in which emitters, usually a critical raw material such as rare-earth or platinum group metal ions, are embedded. Considering the strong ecological impact of their synthesis and the major risk of fossil fuel energy shortage, there is an urgent need to find alternatives. We describe a luminescent nanocomposite based on red-NIR phosphorescent molybdenum nanoclusters, namely Cs2Mo6I8(OCOC2F5)6, embedded in an eco-friendly cellulose biopolymer matrix that is obtained by a simple solvent casting technique. While homogeneity is kept up to 20 wt% of cluster complex doping, annealing hybrids leads to a large increase of their emission efficiency, as demonstrated by quantum yield measurements.

Nanoarchitectonics of Glass Coatings for Near-Infrared Shielding: From Solid-State Cluster-Based Niobium Chlorides to the Shaping of Nanocomposite Films.

The high potential of [{Nb6Cli12}La6] cluster-based building blocks as near-infrared radiation blockers for energy saving applications is exposed in the present paper (i = inner edge-bridging ligand, a = apical ligand of the Nb6; L = H2O and/or Cl). To do so, a combined experimental and theoretical investigation of edge-bridged [{Nb6Cli12}Cla6-x(H2O)x]m+/0/n- cluster unit series (x = 0, 4, 6; m = 2, 3, 4; n = 2, 3, 4) has been carried out. By using the K4[{Nb6Cli12}Cla6] starting solid-state precursor, we explored the behavior of the [{Nb6Cli12}Cla6]4- cluster unit during the different steps of its integration as a building block into a polyvinylpyrrolidone (PVP) matrix to form a glass coating composite denoted {Nb6Cli12}m+@PVP (m = 2 or 3). The optical, vibrational and redox properties [{Nb6Cli12}Cla6-x(H2O)x]m+/0/n- building blocks have been interpreted with the support of electronic structure calculations and simulation of properties. The chemical modifications and oxidation properties have been identified and studied thanks to various techniques in solution. Combining Raman and ultraviolet-visible spectroscopies, electrochemistry, and quantum chemical simulations, we bring new knowledge to the understanding of the evolution of the properties of the [{Nb6Cli12}Cla6-x(H2O)x]m+/0/n- cluster units as a function of the number of valence electron per cluster (VEC) and the nature of terminal ligands (x = 0, n = 4; x = 4, charge = 0; x = 6, m = 4). The fine understanding of the physical properties and vibrational fingerprints depending on the VEC and chemical modifications in solution are mandatory to master the processing of cluster-based building blocks for the controlled design and shaping of glass coating nanocomposites. On the basis of this acquired knowledge, [{Nb6Cli12}Cla6-x(H2O)x]m+/0/n- building blocks were embedded in a PVP matrix. The resulting {Nb6Cli12}2+@PVP nanocomposite film shows excellent ultraviolet (UV, 280-380 nm) and near-infrared (NIR, 780-1080 nm) blocking ability (>90%) and a highly visible light transmittance thanks to the controlled integration of the {Nb6Cli12}2+ cluster core. The figures of merit (FOM) value of Tvis/Tsol (Tvis = visible transmittance and Tsol = solar transmittance) as well as the haze, clarity, and the NIR shielding values (SNIR) were measured. After optimization of the integration process, a {Nb6Cli12}2+@PVP nanocomposite on glass substrate has been obtained with a high FOM equal to 1.29. This high value places the transparent green olive {Nb6Cli12}2+@PVP nanocomposites at the top system in the benchmark in the field of glass coating composites for energy-saving applications.

From Solid-State Cluster Compounds to Functional PMMA-Based Composites with UV and NIR Blocking Properties, and Tuned Hues.

New nanocomposite materials with UV-NIR blocking properties and hues ranging from green to brown were prepared by integrating inorganic tantalum octahedral cluster building blocks prepared via solid-state chemistry in a PMMA matrix. After the synthesis by the solid-state chemical reaction of the K4[{Ta6Bri12}Bra6] ternary halide, built-up from [{Ta6Bri12}Bra6]4- anionic building blocks, and potassium cations, the potassium cations were replaced by functional organic cations (Kat+) bearing a methacrylate function. The resulting intermediate, (Kat)2[{Ta6Bri12}Bra6], was then incorporated homogeneously by copolymerization with MMA into transparent PMMA matrices to form a brown transparent hybrid composite Ta@PMMAbrown. The color of the composites was tuned by controlling the charge and consequently the oxidation state of the cluster building block. Ta@PMMAgreen was obtained through the two-electron reduction of the [{Ta6Bri12}Bra6]2- building blocks from Ta@PMMAbrown in solution. Indeed, the control of the oxidation state of the Ta6 cluster inorganic building blocks occurred inside the copolymer, which not only allowed the tuning of the optical properties of the composite in the visible region but also allowed the tuning of its UV and NIR blocking properties.

Facile and scalable design of light-emitting and ROS-generating hybrid materials made of polyurea gels embedding a molybdenum cluster-based salt.

Here, we demonstrate a facile and scalable preparation via sol-gel chemistry of hybrid polyurea gels containing various amounts of a phosphorescent inorganic octahedral molybdenum cluster-based ternary salt, namely Cs2Mo6Br14. The influence of the Cs2Mo6Br14 content (1-10 wt%) on the polyurea matrix and its physical properties are studied in depth by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and X-ray fluorescence microanalysis (µ-XRF). Regardless of the amount of cluster loaded into the polyurea, the integrity of these species was preserved and their dispersion is homogeneous as shown by µ-XRF mapping. Spectroscopic-structural analyses reveal a significant increase of the chain mobility (glass transition temperature Tg) from -65 °C to -55 °C after the incorporation of Cs2Mo6Br14 (DSC analyses). The FTIR studies show that the homogeneity of the dispersion is ensured by supramolecular interactions between the ether-type oxygen atoms of the PEO chains and the cluster compound. Photoluminescence studies show that the metal cluster emission properties are well retained within the host matrix whatever the loaded content. Such a combination of materials demonstrates the feasibility to fabricate a rubber NIR-emitting device. Moreover, the loaded polyurea is also able to produce reactive oxygen species (ROS) upon irradiation in the UV-A region, opening new perspectives as versatile membranes in the field of photodynamic therapy.

Expanding the Toolbox of Octahedral Molybdenum Clusters and Nanocomposites Made Thereof: Evidence of Two-Photon Absorption Induced NIR Emission and Singlet Oxygen Production.

Bright NIR phosphorescence from octahedral molybdenum clusters has been known since the 1980s. However, their behavior toward NIR excitation has never been investigated. Here we report their abilities to emit NIR light and produce singlet oxygen upon two-photon absorption. This behavior is observed in solution, in the solid state, and when clusters are embedded homogeneously in a poly(dimethylsiloxane) matrix. Such discoveries open new perspectives in several fields like optoelectronics, photodynamic therapy, or bioimaging.

Switchable Two-Dimensional Waveguiding Abilities of Luminescent Hybrid Nanocomposites for Active Solar Concentrators.

Passing from fossil energy sources to renewable ones, meanwhile answering the increasing world energy demand, will require innovative and low-cost technologies. Smart photovoltaic windows could fulfill our needs in this matter. Their transparency can be controlled to manage solar energy and regulate interior temperature and illumination. Here, we present the one-pot synthesis of polymer-dispersed liquid crystals (PDLCs), in which highly red-NIR phosphorescent transition metal clusters are selectively embedded, either in the polymer, in the liquid crystal, or in both phases. The PDLC matrix is used as a tunable waveguide to transfer the emitted light from nanoclusters to the edge of the device, where solar cells could be placed to convert it into electricity. Edge emission is obtained in both "off" and "on" states, with a maximum intensity for the scattering "off" one. These doped PDLCs showing photo-activity features and high stability under voltage represent key stepping stones for integration in buildings, displays, and many other technologies.

Supramolecular Anchoring of Octahedral Molybdenum Clusters onto Graphene and Their Synergies in Photocatalytic Water Reduction.

Dihydrogen (H2) production from sunlight should become one of the most important energy production means in the future. To reach this goal, low-cost and efficient photocatalysts still need to be discovered. Here we show that red near-IR luminescent metal cluster anions, once combined with pyrene-containing cations, are able to photocatalytically produce molecular hydrogen from water. The pyrene moieties act simultaneously as energy transmitters and as supramolecular linkers between the cluster anions and graphene. This association results in a hybrid material combining the emission abilities of pyrene and cluster moieties with the electronic conduction efficiency of graphene. Hydrogen evolution reaction (HER) studies show that this association induces a significant increase of H2 production compared to that produced separately by clusters or graphene. Considering the versatility of the strategy described to design this photocatalytic hybrid material, transition-metal clusters are promising candidates to develop new, environmentally friendly, and low-cost photocatalysts for HER.

When a Red-NIR-Emissive Cs2 [Mo6 Br14 ] Interacts with an Active Diureasil-PEO Matrix: Design of Tunable and White-Light-Emitting Hybrid Material.

Hybrid materials that combine diureasil matrices and octahedral molybdenum clusters have been synthesized to design lead-, cadmium- and rare-earth-free emitters for lighting or optoelectronic applications. This association leads to homogeneous and stable hybrids, for which the emission color can be tailored in the entire visible range, including white light; this is thanks to effective energy transfers from the host to the nanocluster.

Octahedral molybdenum cluster as a photoactive antimicrobial additive to a fluoroplastic.

Finding methods that fight bacterial infection or contamination, while minimising our reliance on antibiotics is one of the most pressing needs of this century. Although the utilisation of UV-C light and strong oxidising agents, such as bleach, are still efficacious methods for eliminating bacterial surface contamination, both methods present severe health and/or environmental hazards. Materials with intrinsic photodynamic activity (i.e. a material's ability upon photoexcitation to convert molecular oxygen into reactive oxygen species such as singlet oxygen), which work with light within the visible photomagnetic spectrum could offer a significantly safer alternative. Here we present a new, bespoke molybdenum cluster (Bu4N)2[{Mo6I8}(CF3(CF2)6COO)6], which is both efficient in the generation of singlet oxygen upon photoirradiation and compatible with the fluoropolymer (F-32L) known for its good oxygen permeability. Thus, (Bu4N)2[{Mo6I8}(CF3(CF2)6COO)6]/F-32L mixtures have been solution-processed to give homogenous films of smooth and fibrous morphologies and which displayed high photoinduced antibacterial activity against four common pathogens under visible light irradiation. These materials thus have potential in applications ranging from antibacterial coatings to filtration membranes and air conditioners to prevent spread of bacterial infections.

Transparent functional nanocomposite films based on octahedral metal clusters: synthesis by electrophoretic deposition process and characterization.

Transparent optical thin films have recently attracted a growing interest for functional window applications. In this study, highly visible transparent nanocomposite films with ultraviolet (UV)-near-infrared (NIR)-blocking capabilities are reported. Such films, composed of Mo6 and Nb6 octahedral metal atom clusters (MC) and polymethylmethacrylate polymer (PMMA), were prepared by electrophoretic deposition on indium tin oxide-coated glass (ITO glass). PMMA was found to improve both the chemical and physical stability of Mo6 and Nb6 MCs, resulting in a relatively homogeneous distribution of the clusters within the PMMA matrix, as seen by microstructural observations. The optical absorption spectrum of these transparent MC@polymer nanocomposite films was marked by contributions from their Mo6 and Nb6-based clusters (absorption in the UV range) and from the ITO layer on silica glass (absorption in the NIR range). Mo6@PMMA nanocomposite films also exhibited excellent photoluminescence properties, which were preserved even after exposure to 50°C at a relative humidity of 70% for one month. These films cumulate high transparency in the visible range with remarkable UV-NIR blocking properties and represent interesting candidates for functional glass application.

Lord of The Crowns: A New Precious in the Kingdom of Clustomesogens.

Replacing pure inorganic materials by functional organic-inorganic hybrid ones to lower production costs has become a major challenge, in particular for the optoelectronic industry. Adding nanostructuration abilities meanwhile preserving homogeneity is even more challenging for this class of new materials. Here we show that red-NIR emissive ternary molybdenum cluster salts can be assembled to liquid crystalline 15C5 crown ethers. The resulting hybrids are homogeneous and stable up to high temperature despite the weakness of the supramolecular interactions binding both components. These are illustrated by 133 Cs MAS NMR. All hybrids show hexagonal columnar arrangements and strong red-NIR emission. Surprisingly, when chlorinated clusters are used instead of brominated ones, the mesophase stability is largely enhanced.

Metal Atom Clusters as Building Blocks for Multifunctional Proton-Conducting Materials: Theoretical and Experimental Characterization.

The search for new multifunctional materials displaying proton-conducting properties is of paramount necessity for the development of electrochromic devices and supercapacitors as well as for energy conversion and storage. In the present study, proton conductivity is reported for the first time in three molybdenum cluster-based materials: (H)4[Mo6Br6S2(OH)6]-12H2O and (H)2[Mo6X8(OH)6]-12H2O (X = Cl, Br). We show that the self-assembling of the luminescent [Mo6L8i(OH)6a]2-/4- cluster units leads to both luminescence and proton conductivity (σ = 1.4 × 10-4 S·cm-1 in (H)2[Mo6Cl8(OH)6]-12H2O under wet conditions) in the three materials. The latter property results from the strong hydrogen-bond network that develops between the clusters and the water molecules and is magnified by the presence of protons that are statistically shared by apical hydroxyl groups between adjacent clusters. Their role in the proton conduction is highlighted at the molecular scale by ab initio molecular dynamics simulations that demonstrate that concerted proton transfers through the hydrogen-bond network are possible. Furthermore, thermogravimetric analysis also shows the ability of the compounds to accommodate more or less water molecules, which highlights that vehicular (or diffusion) transport probably occurs within the materials. An infrared fingerprint of the mobile protons is finally proposed based on both theoretical and experimental proofs. The present study relies on a synergic computational/experimental approach that can be extended to other proton-conducting materials. It thus paves the way to the design and understanding of new multifunctional proton-conducting materials displaying original and exciting properties.

Direct Integration of Red-NIR Emissive Ceramic-like An M6 Xi8 Xa6 Metal Cluster Salts in Organic Copolymers Using Supramolecular Interactions.

Hybrid nanomaterials made of inorganic nanocomponents dispersed in an organic host raise an increasing interest as low-cost solution-processable functional materials. However, preventing phase segregation while allowing a high inorganic doping content remains a major challenge, and usual methods require a functionalization step prior integration. Herein, we report a new approach to design such nanocomposite in which ceramic-like metallic nanocluster compounds are embedded at 10 wt % in organic copolymers, without any functionalization. Dispersion homogeneity and stability are ensured by weak interactions occurring between the copolymer lateral chains and the nanocluster compound. Hybrids could be ink-jet printed and casted on a blue LED. This proof-of-concept device emits in the red-NIR area and generates singlet oxygen, O2 (1 Δg), of particular interest for lights, display, sensors or photodynamic based therapy applications.

Stabilization of Ni2+ dimers in hexacyano Mo6 cluster-based Prussian blue derivatives: experimental and theoretical investigations of magnetic properties.

Herein, two new octahedral molybdenum cyanide cluster compounds, namely [{Ni(NH3)6}4{Ni2(NH3)8}1][Mo6Br6Q2(CN)6]3·12H2O, Q = S (1) and Se (2), have been synthesized as single crystals by slow diffusion of a solution of nickel chloride into aqueous ammonia solutions of a K2Cs2[Mo6Br6Q2(CN)6] molybdenum cyanide cluster-based compound. Both 1 and 2 were structurally characterized by single-crystal X-ray diffraction. They are isostructural and crystallize in the cubic system (Im3[combining macron]m (no. 229); Z = 2, a = 18.147(1) Å, and V = 5976(1) Å3 and a = 18.188(2) Å and V = 6016(2) Å3 for 1 and 2, respectively). 1 and 2 are based on the association of [Mo6Bri6Qi2(CN)a6]4- (Q = S, Se) cluster anions with Ni2+ dimer-based cubic [Ni2(NH3)8]4+ and octahedral [Ni(NH3)6]2+ cations. The structure is based on 2-fold interpenetrated [{Ni(NH3)6}4{Ni2(NH3)8}1][Mo6Br6Q2(CN)6]3 frameworks related to each other by [½, ½, ½] translation. The unit cell is based on a body-centered cubic framework of cubic [Ni2(NH3)8]4+. The [Mo6Bri6Qi2(CN)a6]4- (Q = S, Se) cluster units are located in the middle of the edges and at the center of the faces of the cell. The [{Ni(NH3)6}]2+ cations are located at the center of the cubes of the a/2 edge. The dimers [Ni2(NH3)8]4+ are stabilized by hydrogen bonds between the cyanide ligands of the cluster unit and the hydrogen atoms of the ammonia molecules. Both compounds exhibit a weak antiferromagnetic coupling within the [Ni2(NH3)8]4+ dimer entities at low temperatures together with a paramagnetic behavior originating from the cations of the octahedral [{Ni(NH3)6}]2+ complexes.

Mo6 cluster-based compounds for energy conversion applications: comparative study of photoluminescence and cathodoluminescence.

We report the photoluminescence (PL) and cathodoluminescence (CL) properties of face-capped [Mo6Xi8La6]2- (X = Cl, Br, I; L = organic or inorganic ligands) cluster units. We show that the emission of Mo6 metal atom clusters depends not only on the nature of X and L ligands bound to the cluster and counter-cations, but also on the excitation source. Seven members of the AxMo6Xi8La6 series (A = Cs+, (n-C4H9)4N+, NH4+) were selected to evaluate the influence of counter-cations and ligands on de-excitation mechanisms responsible for multicomponent emission of cluster units. This study evaluates the ageing of each member of the series, which is crucial for further energy conversion applications (photovoltaic, lighting, water splitting, etc.).

Time-gated luminescence bioimaging with new luminescent nanocolloids based on [Mo6I8(C2F5COO)6]2- metal atom clusters.

Bioimaging and cell labeling using red or near infrared phosphors emitting in the "therapeutic window" of biological tissues have recently become some of the most active research fields in modern medical diagnostics. However, because organic and inorganic autofluorophores are omnipresent in nature, very often the background signal from fluorochromes other than targeted probes has to be eliminated. This discrimination could be available using a time-gated luminescence microscopy (TGLM) technique associated with long lifetime phosphorescent nanocomposites. Here, we report new SiO2 nanostructured particle (50 nm in diameter) embedded luminescent nanosized [Mo6I8(C2F5COO)6]2- metal atom clusters (1 nm in diameter), successfully prepared by the microemulsion technique. This combination provides new physical insight and displays red emission in biological based solution under UV-Vis excitation with long lifetimes of around 17 and 84 µs. Moreover, the nanoparticles can be internalized by cancer cells after surface functionalization by transferrin protein and clearly imaged by TGLM under excitation at 365 nm. The nanocomposites have been mainly characterized by scanning and transmission electron microscopies (SEM and HAADF-STEM), UV-Vis and photoluminescence (PL) spectroscopies.

Versatility of the ionic assembling method to design highly luminescent PMMA nanocomposites containing [M6Q(i)8L(a)6](n-) octahedral nano-building blocks.

New luminescent poly(methylmethacrylate) (PMMA) nanocomposites with high content of different hexanuclear octahedral cluster building blocks, namely [Mo6I8(C2F5COO6)](2-), [Re6Se8(CN)6](4-) and [W6Cl14](2-) have been prepared by free-radical polymerisation. To do so, cluster complexes bearing a polymerisable ammonium counter-cation have been synthesised. In this way, we demonstrate that ionic assembling is a powerful tool to functionalise easily any type of anionic cluster units to be introduced in a PMMA organic matrix. All samples remain homogeneous, stable during several months, and retain the luminescence properties of the cluster precursor.

Epoxy Based Ink as Versatile Material for Inkjet-Printed Devices.

Drop on Demand inkjet printing is an attractive method for device fabrication. However, the reliability of the key printing steps is still challenging. This explains why versatile functional inks are needed. Epoxy based ink described in this study could solve this critical issue because it can be printed with low drawbacks (satellites droplets, long-lived filaments, etc.). Moreover, a wide concentration range of solute allows the fabrication of films from thin to high aspect ratio. Optimizing experimental parameters (temperature, overlap) and ink composition (single or cosolvent) is useful to tune the film profile. As a result, many shapes can be obtained such as donuts or hemispherical caps for a droplet and smooth or wavy shape for a thin film. This study demonstrates that epoxy based versatile ink can be used in numerous fields of applications (organic electronics, optics, sensors, MEMS, etc.). To prove this assertion, organic field effect transistors and light emitting films have been fabricated.

From Mesomorphic Phosphine Oxide to Clustomesogens Containing Molybdenum and Tungsten Octahedral Cluster Cores.

New clustomesogens (i.e., metal atom clusters containing liquid crystalline (LC) materials) have been obtained by grafting neutral cyanobiphenyl (CB)- or cholesteryl-containing tailor-made dendritic mesomorphic triphenylphosphine oxide ligands on luminescent (M6 Cl(i) 8 )(4+) octahedral cluster cores (M=Mo, W). The LC properties were studied by a combination of polarizing optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray powder diffraction analyses. While the organic ligands showed various mesophase types ranging from nematic, SmA columnar (SmACol ), SmA, and SmC phases, it turned out that the corresponding clustomesogens formed layered phases (SmA) over a wide range of temperatures that depend on the nature and density of mesogenic groups employed. Intrinsic luminescence properties of the cluster precursors are preserved over the entire range of LC phase existence.