Hybrid organic inorganic liquid crystal materials containing luminescent transition metal clusters – CLUSTOMESOGEN

One nanometre-sized [M6L14]n- units (M = Mo, Re; L = halogen, chalcogen, 1< n <8) can be highly emissive in the red-NIR area (photoluminescence quantum yields up to 0.23). Their incorporation into LCs will lead to multifunctional nanomaterials with very interesting optical and electronic properties due to synergetic effects: self assembling of anisotropic LC combined with photoluminescence of clusters.
Molecular engineering of LC is an important issue to control self-assembling and self-organization processes of single entities into periodically ordered meso- and nanostructures. Yet, dendritic structures are interesting frameworks where LC properties can be modulated by subtle modifications of the dendritic connectivity. The project aims to combine the world of LC dendrimers with the one of solid state chemistry by designing and studying LC supermolecules (dendrimers) containing luminescent transition metal cluster as their core. It will use a dual experimental/modelling approach to understand the self-assembling processes and target specific supramolecular architectures, thanks to the complementary skills of participants. The CLUSTOMESOGEN project is of peculiar interest to academics from a range of backgrounds: while the targeted materials synthesis calls on solid state, organic, coordination and supramolecular chemistries, the studies of the LC properties and luminescence require expertise in Physical-Chemistry, Molecular Modelling, and Physics and their integration into devices like LASER or wavelength tunable waveguides involves optics and physics know-how. All the necessary skills are available in the consortium to develop the different parts of the project. The interest of CLUSTOMESOGEN is also increased by the will of participants to insert these original molecular objects into optics dedicated devices.

Numerous compounds have been obtained according to the two approaches described in the project (ionic and covalent strategy), as planned. The liquid crystal and photophysical studies realized up to now, allow us to observe general trends about the optimal morphology needed to i) observe a liquid crystalline behavior, ii) get miscible hybrids with commercially available liquid crystalline mixtures, and more importantly iii) obtain stable mixtures over large periods and in operational conditions (integration in LC cells and application of a voltage).
A new approach has been recently discovered (the supramolecular approach). This strategy enables the direct integration of solid state ternary cluster compounds of general formula AxM6X14 in a liquid crystalline material.

This project generated yet 3 publications in:
Chem. Eur. J., 2014, 20, 8561-8565
J. Mater. Chem. C, 2014, 2, 9813
Chem. Commun., 2015, 58, 3774-3777
Some of the results were presented in International conferences:
International Conference on multifunctional, hybrid and nanomaterials, 9-13/03/2015, Sitges, Spain
International Liquid Crystal Conference, 29/6-04/07/2014, Dublin, Ireland

The project follows smoothly the initial plan. First results in the frame of the covalent approach indicate that these class of clustomesogens may not be stable in operational conditions (under application of a voltage in a LC cell). Therefore, we will replace from now the covalent approach by the supramolecular strategy that we discovered recently. Thus, we will use this way to design new clustomesogens and study their behavior under application of an electric field once they are integrated in a LC device. From the molecular dynamic calculations point of view, the ‘all atoms’ approach, too time consuming, will be replaced by a “united atoms” strategy. Its force field is under construction.

«Thermotropic Luminescent Clustomesogen Showing a Nematic Phase: a Combination of Experiments and Molecular Simulation Tools«, Amela-Cortes, M.; Dorson, F.; Prévôt, M.; Ghoufi, A.; Fontaine, B.; Goujon, F.; Gautier, R.; Cîrcu, V.; Mériadec, C.; Artzner, F.; Folliot, H.; Cordier, S.; Molard, Y. Chem. Eur. J., 2014, 20, 8561-8565


“From Metallic Cluster-based Ceramics to Nematic Hybrid Liquid Crystals: A Double Supramolecular Approach”, S. K. Nayak, M. Amela-Cortes, C. Roiland, S. Cordier, Y. Molard, Chem. Commun., 2015, 58, 3774-3777

“Hexacyano octahedral metallic clusters as versatile building blocks in the design of extended polymeric framework and clustomesogens”, M. Amela-Cortes, S. Cordier, N. G. Naumov, C. Meriadec, F. Artzner, Y. Molard, J. Mater. Chem. C, 2014, 2, 9813.

The CLUSTOMESOGEN project aims to synthesize and study functional liquid crystal containing metallic clusters as luminescent inorganic dyes in the Red-NIR area. These studies will orient the design of devices demonstrating the high potential of such materials in optic and optoelectronic applications. Preliminary results, published in Angew. Chem. in 2010 and Chem. Mater. in 2011, demonstrate the concept of such class of functional materials. The CLUSTOMESOGEN project will let us explore and develop efficiently the potentialities of this new class of materials by giving us the mandatory human and material supports. Liquid crystals (LC) are the molecular materials of the present day since they are extensively used as the high technology materials found in low power, flat-panel displays known as LCDs or are also found in diverse applications such as temperature sensing, solvents in chemical reactions, or in the fields of spectroscopy, holography, or biomedical, etc. In addition to their exceptional self-assembly abilities in the solid state or in solution, properties such as luminescence, redox states and/or magnetism can be incorporated inside LC materials. Controlling the molecular aggregation in the LC phases allow then, the fine tuning of the optical and electronic properties of the emergent organization. Synthesis of such multifunctional materials is a challenging area of research since new properties and applications can emerged from their comprehensive studies. Metal clusters are aggregates of few metal atoms held together by metal-metal bonds. They show unusual electronic, magnetic and optical properties due to the full delocalisation of valence electrons on the whole metallic architecture. In particular, one nanometre-sized [M6L14]n- units (M = Mo, Re; L = halogen, chalcogen, 1< n <8) can be highly emissive in the red-NIR area (photoluminescence quantum yields up to 0.23). Their incorporation into LCs will lead to multifunctional nanomaterials with very interesting optical and electronic properties due to synergetic effects: self assembling of anisotropic LC combined with photoluminescence of clusters.
Molecular engineering of LC is an important issue to control self-assembling and self-organization processes of single entities into periodically ordered meso- and nanostructures. Yet, dendritic structures are interesting frameworks where LC properties can be modulated by subtle modifications of the dendritic connectivity. The project aims to combine the world of LC dendrimers with the one of solid state chemistry by designing and studying LC supermolecules (dendrimers) containing luminescent transition metal cluster as their core. It will use a dual experimental/modelling approach to understand the self-assembling processes and target specific supramolecular architectures, thanks to the complementary skills of participants. The CLUSTOMESOGEN project is of peculiar interest to academics from a range of backgrounds: while the targeted materials synthesis calls on solid state, organic, coordination and supramolecular chemistries, the studies of the LC properties and luminescence require expertise in Physical-Chemistry, Molecular Modelling, and Physics and their integration into devices like LASER or wavelength tunable waveguides involves optics and physics know-how. All the necessary skills are available in the consortium to develop the different parts of the project. The interest of CLUSTOMESOGEN is also increased by the will of participants to insert these original molecular objects into optics dedicated devices. As stated in the Strategic Research Agenda of the European Technology Platform ‘SusChem’, such an innovative project in nanosciences has a high industrial potential in the medium and long term.