School of Chemistry Colloquia: Dr Anthoula Papageorgiou Tethering and assembling N-heterocyclic carbenes on planar metal surfaces
N-heterocyclic carbenes (NHCs) are strong ligands and a promising alternative to thiols for self-assembled monolayers. However controlling their adsorption on solid surfaces is a current challenge of surface functionalization. I will introduce our recent work, that focuses on understanding [Chem. Sci., 2017, 8, 8301] and controlling the assembly of NHCs on metal-vacuum interfaces. Our analysis encompasses an integration of microscopy, diffraction, spectroscopy and desorption in ultra-high vacuum combined with theoretical considerations to generate a high degree of precision in the understanding of interfacial processes at the atomic level. To control the NHC tethering we exploited the surface chemistry of a well-established building block for on-surface assembly: a porphyrin [J. Phys. Chem. C, 2021, 125, 3215; Angew. Chem. Int. Ed., 2021, 60, 16561]. A suitable metalloporphyrin is a pedestal that orients and defines the lateral arrangement of NHCs on a planar surface by providing a single atom site. We applied NHCs on a self-assembled metalloporphyrin layer and discovered that they are suitable pillars for the formation of out-of-plane architectures [J. Am. Chem. Soc., 2021, 143, 4433]. The resulting modular arrangement of NHCs allows us to address individual ligands by controlled manipulation with the tip of a scanning tunnelling microscope, creating patterned structures on the nanometer scale. Under certain conditions, we also observed a fascinating, dynamic interface rearrangement based on the NHC ligand acting as a molecular porter for metalloporphyrin molecules: they transfer porphyrin molecules from the first to the second molecular layer. Harnessing these dynamic events will serve the engineering of atomically precise NHC-containing complex interfaces.