The ERC project SURFLINK aims to fabricate surface-supported covalently-linked molecular networks in a bottom-up approach, which are characterized by scanning probe microscopy techniques. Specially designed molecular building blocks are used to create low-dimensional carbon-based materials, in particular, functionalized 2D networks with tunable electronic properties and nanometer-sized pores. We successfully fabricated porous surface-supported nanostructures including macrocycles, 1D nanoribbons, and long-range ordered 2D networks on metal surfaces via Ullmann-type coupling and other coupling reactions reactions. Some of the main achievements of SURFLINK include:
I. We achieved to grow high-quality covalently-linked 2D networks using a hierarchical synthesis, where hexagonal macrocycles and chains were assembled in a first reaction step and connected to extended porous networks in a second reaction step. We used thereby N-heterotriangulene as precursors. We demonstrated experimentally for the first time in carbon structures produced by on-surface synthesis the reduction of the electronic bandgap going from the monomer to the one-dimensional chains and the two-dimensional networks using scanning tunneling spectroscopy (STS), thus corroborating the extension of the effective pi-system (Nat. Comm. 2017).
II. We successfully demonstrated the on-surface synthesis of 1D porous carbon nanoribbons via a preprogrammed isomerization of conformationally flexible polymer chains (JACS 2017).
III. We unraveled the properties of metallated graphyne-like networks as 2D materials. Organometallic networks use the advantage of a reversible structure formation in contrast to C-C coupling reactions. We studied the electronic structure and the covalent bond character of surface-supported organometallic networks with Ag-bis-acetylide bonds. STS revealed a frontier, unoccupied electronic state that is delocalized along the entire organometallic network and that proves the covalent nature of the Ag-bis-acetylide bonds. (Nanoscale 2018, ACS Nano 2020)
IV. We investigated the host-guest chemistry in triphenylamine-based COFs and identified strategies for supermolecular doping in COFs. (Nanosclae 2021)
V. Concerning the bulk insulating surfaces, an in-situ cleaver was built, and suitable preparation procedures were developed for several salt and metal oxide surfaces. We achieved atomically-resolved imaging on those surfaces using non-contact atomic force microscopy (nc-AFM) and have characterized common surface defects, which might act as reactive centers to initiate surface reactions. Controlled structure formation of one-, two-, and three-dimensional triphenylamine derivatives was demonstrated on KBr and presented by means of nc-AFM measurements in combination with DFT calculations.
