Controlled Reactivity of Sulfoxides on Insulating Surfaces – CROSS

On-surface synthesis has emerged as a powerful way to produce new functional nanomaterials and extended molecular structures, which cannot be prepared by “conventional” in-solution synthetic chemistry. Starting from tailor-made molecular precursors, a variety of complex nanoarchitectures exhibiting specific structural, chemical, optoelectronic and magnetic properties have been obtained with a high degree of control.
The vast majority of on-surface reactions at the solid-vacuum interface has been achieved on metallic surfaces to take advantage of their catalytic activity and of their compatibility with Scanning Tunneling Microscopy for the direct characterization of products. However, such underlying substrates strongly modify the optoelectronic properties of adsorbed species, which is a major limitation regarding building blocks reactivity and products functionality. Insulating substrates thus appear as highly promising alternatives for on-surface synthesis, allowing for novel photoreactivity pathways and for direct investigations of intrinsic optoelectronic properties of the newly-formed nanostructures, as a starting point for their optimization and future applications. On-surface synthesis on insulating substrates is still in its infancy though, with only scarce reports to date of successful reactions on bulk insulators. The key challenge lies in the absence of catalytic activity of the surface, while possibilities for thermal activation are limited due to weak molecule-substrate interactions. The main objective of the CROSS project aims at lifting these barriers and expanding the scope of chemical reactions, in particular photoinduced processes, operative on insulating substrates.
In addition, research in the newly-developing field of on-surface synthesis has primarily been focused on the covalent assembly of the target 1D- and 2D-extended frameworks by intermolecular couplings, while the internal structure of such scaffolds may be modified by intramolecular reactions on surface. However, methods available for functional modifications in a given covalent framework on surface are extremely rare, which inherently limits the modularity of multistep synthetic strategies on surfaces. In “conventional” in-solution chemistry, interconversions of organic functions are typically achieved by addition of appropriate (in)organic reagent(s) to the reaction medium. On surfaces under Ultra-High Vacuum, the implementation of similar strategies for functional group interconversion is still hampered by complex challenges related to the control of intermolecular reactivity between two non-equivalent molecular partners, i.e. between the reactant and a sacrificial reagent. With an original multidisciplinary approach combining thorough in-solution and on-surface investigations, the CROSS project will develop new and widely-applicable tools for on-surface synthesis on insulating substrates, using photoreactive polar sulfoxides as sacrificial chemical reagents to trigger selective reactions in-situ.
The CROSS project, organized in three scientific tasks, thus aims at:
1) characterizing the structural, electronic and optical properties of sulfoxides adsorbed on insulating substrates and investigating their photoreactivity as compared with their photochemical behavior in solution;
2) exploiting sulfoxides as photoactivatable oxygen transfer agents for in-situ functional modifications of a variety of (metallo-)organic structures on insulating substrates;
3) exploiting sulfoxides as photocleavable vector ligands for the delivery of catalytically-active metal atoms on insulating substrates.