EXtended Polyoxometetalate Assemblies: a Nanostructuration Design – EXPAND

The development of nanostructured molecular materials is a major scientific challenge for various contemporary societal issues. In this context, elaboration of materials of suitable properties integrating polyoxometalates (POMs) as molecular building blocks is particularly attracting owing to their various properties and potential applications. EXPAND aims at synthesizing finite and 2D mesoscopic POM-based nanostructures via metal-directed self-assembly processes. The approach relies on the synthesis of rigid POM-based building blocks bearing covalently bonded ligands with well-suited orientations and denticities (Task 1). Coordination of these hybrid building blocks to complementary metal ions with available coordination sites will straightforwardly afford various self-assembled architectures with attractive properties. Different types of assemblies will be foreseen: mesoscopic cyclic coordination oligomers (task 2) and 2D networks (task 3) from ditopic and tritopic POM-based hybrid building blocks respectively. Owing to the ionic character of POMs, aggregation of the primary self-assembled systems through intermolecular electrostatic interactions should afford larger multi-scale assemblies. The control of the aggregation process of these supramolecular assemblies will constitute an important aspect of this project. In addition to the classical analytical techniques of POM-based hybrids, new methods will be developed to characterize the supramolecular assemblies according to their morphology (discrete cyclic oligomers, nano-aggregates, monolayers, molecular films…). A major advantage of the proposed approach is to enable control of the dimensionality (from 0D to 2D) according to the pre-determined geometric patterns of the POM-based (number and mutual orientation of appended ligands) and the metal linker units and the overall intermolecular interactions (electrostatic and hydrophobic especially). According to their morphology, the systems will display different properties that should find applications in various research fields. As a first step, each system will be tested in a specific application: nano-aggregates as host-material for light upconversion, nanoporous 2D monolayers for surface nano-patterning and 2D nanofilms as conductive interfacial layer (task 4). The objectives of this project involve not only the design, formation and characterization of finite and 2D supramolecular POM-based architectures but also the understanding and control of their multi-scale organization as well as the development of a few specific applications.