CrystOS

The objective of this project is to explore new synthetic routes, which will allow a breakthrough towards the elaboration of crystalline, porous, three-dimensional covalent hybrid silica networks. One of the main characteristics of the hybrid organic silica network, resulting from hydrolysis of organotrialkoxysilanes is that the hydrolysis and poly-condensation is a kinetically controlled process. Consequently, most hybrid silicas prepared by this sol-gel route are amorphous materials. Some structuring has been successfully achieved over the last ten years. The control of the pore structure was obtained in some cases by using organic surfactants as external template but it is limited to “small” organic substructure or to low organic content within the material. Moreover whereas ordered mesopores structures are accessible, only phenylene bridged silica exhibited molecular periodicity in the pore walls. We proposed another approach to achieve some nanostructuration upon taking advantage of intermolecular interactions between monomeric units during the poly-condensation process. It allowed the synthesis of self-organised hybrid silicas, by a transcription of the structure of supramolecular assemblies of precursors into hybrid three-dimensional networks. However the medium long-range ordering is most often limited to a lamellar arrangement of the organic substructures. Whereas crystalline covalent network such as MOF or COF are receiving attention, the synthesis of crystalline covalent hybrid silica networks remains a challenge. The crystal structure and the materials properties could be varied or tuned according to the nature of the organic component in the hybrid silica networks. Crystalline organosilicas will constitute a new class of covalent solids with tunable properties of interest for useful application in many areas. We propose to explore the synthesis of hybrid silica under thermodynamically controlled reaction conditions. The syntheses will be achieved under reaction conditions where Si-O or (and) C-C bonds will form reversibly or using dynamic combinatorial chemistry. These will therefore allow self-healing of the covalent network to generate the more stable crystalline structural arrangement. The proposal is an exploratory project with fundamental challenges. However from our experience with self-assembled organosilicas, we will explore the properties, which can be expected in these crystalline materials. We will take advantage of the regular and tunable pore structure within the crystalline network and also explore the properties associated to the introduction of organic pi-conjugated organic substructures and to their intermolecular interactions in the crystalline network. We will first focus on sorption properties of the porous organic-inorganic network and also study some optical and electro-optical properties associated to the introduction of organic pi-conjugated substructures as bridging units in the hybrid network. A variety of uses can be envisaged for crystalline organosilicas, some of them will be evaluated and will receive more attention as this new class of materials develops beyond the scope of this exploratory proposal.