COVANET

The realization of molecule-based miniature devices with advanced functions requires the development of new and efficient approaches for combining molecular building blocks into desired functional structures. Supramolecular chemistry concepts have been largely exploited to produce controlled structures thank to selective and directional non-covalent interactions. More recently, these concepts have been widely applied to molecular systems at surfaces to produce two-dimensional organic layers with specific properties. However, because of the weak nature of these non-covalent bonds the networks lack the necessary stability to be used for the patterning of practical nano-technology devices. The main aims of the project are to synthesize new functional building-blocks and to develop novel routes to produce covalent nanoporous organic frameworks with the objective of immobilizing well-defined functionalities (metal/magnetic atoms, gas sensing, hydrogen storage, biocompatible functions, etc…) inside the pores. This work is supported by recent reports demonstrating a significant improvement of the stability of the organic monolayers resulting from covalent linkages between elementary building-blocks. These organic films constitute ideal candidates to immobilize transition metal atoms. Metal ions incorporated in supramolecular structures possess multiple electronic/spin states and a related variety of redox, photochemical, and magnetic properties. These systems represent some of the most interesting materials for the fabrication of functional devices, including nanoscale molecular catalysts, sensors, electronic and magnetic components. In this project we propose to realize self-assemblies of highly ordered molecular monolayers on surfaces, still based on the generation of boroxines starting from boronic acids. Originality of the boronic acids that we propose to synthesize lies in the fact that heteroatoms will be introduced in the core ring or at the periphery of the aromatic rings. Presence of these heteroatoms is first devoted to improve the anchorage of the monolayer onto the surface by use of the diffuse character of the orbitals. Secondly, based on the fundamental principle of coordination chemistry, these electron-rich heteroatoms will interact with electrodeficient transition metal atoms via their non-bonding electrons and act as stabilizing agent to maintain and immobilize metals in the nano-cavities of the organic framework. This will be processed through in situ vapor-deposition of metal atoms. Reduction of the cation can be expected by the surface, eventually after thermal annealing. We also intend to study the chelation properties of the frameworks used in this project and to adapt the size of the cavities in order to favor the stability of the metallated frameworks. The characterization of the frameworks will be done at the molecular scale by scanning tunneling microscopy (STM).