Thermotropic Luminescent Clustomesogen Showing a Nematic Phase: A Combination of Experimental and Molecular Simulation Studies

Joint Venture of Metal Cluster and Amphiphilic Cationic Minidendron Resulting in Near Infrared Emissive Lamellar Ionic Liquid Crystals

Inorganic red-NIR emissive materials are particularly relevant in many fields like optoelectronic, bioimaging or solar cells. Benefiting from their emission in devices implies their integration in easy-to-handle materials like liquid crystals, whose long-range ordering and self-healing abilities could be exploited and influence emission. Herein, we present red-NIR emissive hybrid materials obtained with phosphorescent octahedral molybdenum cluster anions electrostatically associated with amphiphilic guanidinium minidendrons. Polarized optical microscopy and X-ray analysis show that while the minidendron chloride salts self-organize into columnar phases, their association with the dianionic metal cluster leads to layered phases. Steady-state and time-resolved emission investigations demonstrate the influence of the minidendron alkyl chain length on the phosphorescence of the metal cluster core.

Mixed-metal clusters with a {Re3Mo3Se8} core: from a polymeric solid to soluble species with multiple redox transitions

Soluble compounds based on new heterometallic {Re₃Mo₃Se₈}ⁿcluster cores were synthesized and investigated.

Clustomesogens: Liquid Crystalline Hybrid Nanomaterials Containing Functional Metal Nanoclusters

Inorganic phosphorescent octahedral metal nanoclusters fill the gap between metal complexes and nanoparticles. They are finite groups of metal atoms linked by metal-metal bonds, with an exact composition and structure at the nanometer scale. As their phosphorescence internal quantum efficiency can approach 100%, they represent a very attractive class of molecular building blocks to design hybrid nanomaterials dedicated to light energy conversion, optoelectronic, display, lighting, or theragnostic applications. They are obtained as AnM6X(i)8X(a)6 ternary salt powders (A = alkali cation, M = Mo, Re, W, X(i): halogen inner ligand, X(a) = halogen apical ligand) by high temperature solid state synthesis (750-1200 °C). However, their ceramic-like behavior has largely restricted their use as functional components in the past. Since these last two decades, several groups, including ours, started to tackle the challenge of integrating them in easy-to-process materials. Within this context, we have extensively explored the nanocluster ternary salt specificities to develop a new class of self-organized hybrid organic-inorganic nanomaterials known as clustomesogens. These materials, combine the specific properties of nanoclusters (magnetic, electronic, luminescence) with the anisotropy-related properties of liquid crystals (LCs). This Account covers the research and development of clustomesogens starting from the design concepts and synthesis to their introduction in functional devices. We developed three strategies to build such hybrid super- or supramolecules. In the covalent approach, we capitalized on the apical ligand-metal bond iono-covalent character to graft tailor-made organic LC promoters on the {M6X(i)8}(n+) nanocluster cores. The supramolecular approach relies on the host-guest complexation of the ternary cluster salt alkali cations with functional crown ether macrocycles. We showed that the hybrid LC behavior depends on the macrocycles structural features. Finally, a third strategy, known as the ionic-assembling strategy, exploits the anionic character of the [M6L14](n-) nanocluster units whose charge is counterbalanced by tailor-made organic cations. We first focused on rationalizing the structural-LC behavior relationships of these noncovalent nanostructured materials by using NMR, SAXS, DSC, and POM technics. Depending on the hybrid organic-inorganic volumic fraction, thermotropic layered or nematic phases were observed. In this last case, the nematic phase being the most fluid of all LC phases, we further investigated this class of clustomesogen by introducing them in electro-controlled devices to tune either their photoluminescence or observe polarized emission. We hope this Account will provide useful tools for the development of new materials integrating such bright but still underused inorganic phosphors.

Ionic Liquid Crystals: Versatile Materials

This Review covers the recent developments (2005-2015) in the design, synthesis, characterization, and application of thermotropic ionic liquid crystals. It was designed to give a comprehensive overview of the "state-of-the-art" in the field. The discussion is focused on low molar mass and dendrimeric thermotropic ionic mesogens, as well as selected metal-containing compounds (metallomesogens), but some references to polymeric and/or lyotropic ionic liquid crystals and particularly to ionic liquids will also be provided. Although zwitterionic and mesoionic mesogens are also treated to some extent, emphasis will be directed toward liquid-crystalline materials consisting of organic cations and organic/inorganic anions that are not covalently bound but interact via electrostatic and other noncovalent interactions.

Combined theoretical and time-resolved photoluminescence investigations of [Mo6Bri8Bra6]2− metal cluster units: evidence of dual emission

Distinct emissive species have been identified in [Mo₆Brⁱ₈Br^a₆]²⁻ containing systems. Strong geometrical relaxations of the triplet excited states are responsible for the huge energy shift leading to intense red-NIR emission.

From metallic cluster-based ceramics to nematic hybrid liquid crystals: a double supramolecular approach

Luminescent bulky anionic inorganic species are directly integrated in a liquid crystalline material by a double supramolecular approach combining host–guest and electrostatic interactions.

Tuned red NIR phosphorescence of polyurethane hybrid composites embedding metallic nanoclusters for oxygen sensing

Phosphorescent metallic clusters are functionalized and integrated in polyurethane by copolymerization. Solid state quantum yield measurements show a drastic and reversible enhancement of nanocomposite luminescence depending on its surrounding atmosphere.