Surface-directed Elaboration of Two-dimensional Nanoporous Covalent Organic Frameworks ) – DUALITY

Single-layered surface covalent organic frameworks (SCOFs) are a new class of porous polymers with structural periodicity in the skeleton and predesignable pore parameters. Up to now, most of the SCOFs have been prepared by Ullmann dehalogenation reactions of brominated aromatic compounds or trimerization of diboronic acids. If the side-product released during the first reaction is quite aggressive (Br2), the availability of monomers for the second one is extremely limited as a result of difficult synthesis. In this work, we propose to overcome these two problems by using the Knoevenagel condensation for SCOF formation. Application of Knoevenagel reaction to polymerized monolayers on surface is unprecedented in the literature. The preliminary results we obtained in this field evidenced our monomer to exhibit an unexpected dual reactivity. Two possible reaction pathways were evidenced, the choice of the reaction type being directed by the crystallographic orientation of the surface, namely the oxidative coupling or the Knoevenagel reaction. Based on these recent and pioneering works on surface-directed reactions, we propose to get a deeper insight into the mechanisms governing the dual reactivity of our monomers and to create novel well-defined functionalized and extended covalent networks. The objectives of the present project are three-fold: 1) to develop new monomers aiming at optimizing the reaction advancement, offering a better control on the supramolecular pattern and reduction of the number of defects 2) to emphasize the difference types of bond formed and determined the reaction path involved during the different coupling. To reach this goal, the vibrational properties of the SCOFs will be investigated by scanning tunnelling microscopy combined with high-resolution electron energy loss spectroscopy (HREELS).
The electronic properties will be characterized by photoemission spectroscopy (XPS/UPS). 3) to introduce functionalities in the backbone of the polymer network, investigate new shape of polygons or introduce nitroxide groups that could be later used for the polymer growth in the third dimension.