Covalent crystalline organosilica networks – CrystOS

The project was developed in two approaches: - The first one aimed at the elaboration of organosilicas under reversible conditions to reach materials whose three-dimensional structure is organized. Two main routes have been explored: i) Synthesis or reorganization of materials under thermodynamic control or reversibility conditions. Experimental conditions for the reversible cleavage and formation of Si-O or C-C bond have been studied with model molecules in particular: hydrothermal conditions for formation of Si-O bonds, Si-O cleavage in the presence of fluorides, metathesis of C = C bonds. ii) Elaboration of elementary silica blocks functionalized or endowed with molecular recognition properties, followed by their self-assembly by dynamic covalent chemistry or by hydrogen bonding. - The second approach relies on the synthesis of organosilicas containing extensive pi-conjugated systems whose self-organization relies on the interactions between the pi systems. Their thin-film forming allows them to be used as a sensitive material for optoelectronic devices. Hybrid field-effect transistors show exceptional stabilities while delivering exploitable performance.

- Synthesis of organosilicas by self-assembly of silica bricks functionalized by carboxylic acids leading to a crystalline and porous hybrid material opening to a path towards the construction of 3D networks of metallo-organosilicas. - Synthesis of a new family of bis-benzothiophene semiconductors functionalized and organized by supramolecular engineering. - Synthesis of a diol derivative of self-assembled hydrogen-bonded bis-benzothiophene showing an exceptional negative thermal expansion in the solid state. This results in a new collaboration for understanding and modeling this phenomenon. - The production of thin layers introduced as sensitive material for particularly stable field effect transistors, the hybrid and covalent structure of the material resistant to solvents in the presence of ultrasound.

The work carried out within the framework of the CrystOS project allowed to identify access routes to organized organosilicas. While the covalent dynamic chemistry approach has not been successful in our hands, the non-covalent pathway has made it possible to obtain the first crystalline organosilicas by assembling organosilicon precursors by hydrogen bonds. This route is generalizable to other precursors and the polycarboxylic acids obtained open the possibility of using coordination chemistry to make new metallo-organosilicon assemblies. The self-organization of hybrid silicas in thin layers could be carried out with a new pi-conjugated system derived from bis-benzothiophene. The materials obtained showed particularly interesting performances: charges transport with high mobilities, transistor effect of the thin films incorporated in OFET, negative thermal expansion resulting from the hydrogen bond assemblies, stability of the assemblies by covalent bonds incorporated in the OFET. On the one hand, the ongoing development of hybrid thin films for transistors is envisaged from novel asymmetric monofunctional analogs of bis-benzothiophene. On the other hand, new collaborations have been set up to study and rationalize the negative thermal expansion in our materials and its extension to other donor or acceptor of hydrogen bonds.

1) In massive materials, the dynamic noncovalent chemistry applied to the POSS-Acid made it possible to obtain a perfectly crystalline supramolecular material, the study of which was described in CrystEngComm, 2017, 19, 492-502. 2) In thin film, the study of the structural properties of alcohol derived from BTBT was published in J. Mater. Chem. C, 2016, 4, 6742-6749 and selected as part of the «2016 Journal of Materials Chemistry C Hot Papers«. A paper describing the properties of negative thermal expansion is submitted to J. Amer. Chem. Soc. The control of the aggregation of the silylated derivative of the BTBT offering not only hybrid but also extremely stable transistors facing the solvents led to a first publication in Adv. Elec. Mater, 2017, 1700218.