On-surface synthesis of covalent networks with integrated optical functions – PHOTONET

The engineering of highly organized systems from instructed molecular building blocks opens up new vistas for the control of matter and the exploration of nanodevice concepts. Supramolecular self-assembly at surfaces has proven in the last two decades to be very efficient for creating atomically-controlled organic nanostructures. The non-covalent character of intermolecular interactions provides high flexibility (reversibility) and defect self-healing that is required to produce perfectly ordered and well-extended superstructures. Molecular architectonic on surfaces represents thus a versatile rationale to realize structurally complex nanosystems with specific shape, composition, and functional properties, which bear promise for technological applications. In addition, well-defined surfaces provide versatile platforms for steering and monitoring in-situ the assembly of molecular nanoarchitectures in exquisite detail. In particular, scanning probe microscopy techniques provide unparalleled spatial resolution and versatility. The large number of published studies and review articles dealing with supramolecular self-assemblies at surfaces demonstrates it as a mature field. However, the low stability and the lack of electronic communication between the molecules in such networks prevent from practical applications in harsh environments. In this regard, the possibility of extending the concepts of supramolecular chemistry to the formation of covalent bonds between molecular tectons has attracted recent focus, leading to the emergence of the field of on-surface synthesis. While two-dimensional (2D) polymers are expected to have great impact on many fundamental and applied aspects of science, the search for synthetic route leading to reliable and robust periodic covalent molecular sheets is still in infancy. Nevertheless, the demonstrations of covalent polymerization performed directly at surfaces are opening promising perspectives and are raising a wide international interest.
The PHOTONET project aims at developing an adaptive 2D polymer as a universal scheme for creating robust organic surfaces possessing integrated optical functions. To this target, a variety of surface-supported extended covalent networks will be formed through in-situ reaction of the precursors. The strategy proposed enables incorporation of targeted molecular functions into large scale, extended regular networks while preserving the original molecular-level physicochemical properties. High level of control on the shape, dimensionality, chirality and functionality of the covalent networks will be demonstrated. The project includes basic investigations at the single molecule level as well as structural and spectroscopic characterizations of extended networks, on metal or insulating substrates.
The development of the new optical materials targeted in the PHOTONET project will have long-term applications in a wide range of different domains: light-emitting devices and photovoltaics, molecular memory, magnetism, catalysis, chiral surfaces, intelligent membranes. The advanced physicochemical characterization and the measurement of the optical activity of the systems will represent the proof of concept for the targeted properties. In addition, the elaboration of the networks on insulating substrates will represent an important breakthrough towards practical applications in real devices. Because the covalent systems to be developed can host a large variety of functions such as organometallic catalysts, magnetic centers, chiral surfaces, membranes, the PHOTONET project will be able to address important societal challenges like green and environmental chemistry, smart materials, energy, flexible electronics, information technology.