On-Surface Synthesis of Regular 2D Polymers – Novel Structures, Properties, and Synthetic Routes

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Project aim is to develop, study and establish novel methods for the synthesis of regular functional 2D polymers on inert solid surfaces under ultra-high vacuum conditions. The syntheses in the first part are carried out through the direct deposition of poly-radicals that react into C-C bonded networks through additions on the surfaces. These radicals are generated from precursor molecules in a radical-deposition-source (RaDeS) upon deposition by the dissociation of halogen-substituents. The newly devised RaDeS features an integrated cooling stage that reduces the thermal energy of the poly-radicals sufficiently to allow for stationary adsorption on weakly interacting surfaces. Thereby, the growth of 2D polymers with exceptional structure quality can be expected, owing to the combination of high monomer mobility and low reaction temperatures, as compared to the conventionally used metal surfaces. Syntheses are focused on graphitic surfaces and structural characterization of the 2D polymers will be primarily carried out by high-resolution Scanning-Probe-Microscopy.The impact of molecular structure and the most important reaction parameters deposition rate and reaction temperature is fundamentally studied on polyphenylene 2D polymers. The synthesis of functional 2D polymers will be based on these experiences: conjugated 2D polymers are synthesized from thiophene based monomers. Their electronic structure will be characterized locally by tunneling spectroscopy and globally by photoelectron spectroscopy. Porphyrin-based 2D polymers are synthesized from established tetraphenylporphyrin precursors and post-synthetically functionalized by on-surface metalation. Finally, we will explore synthesis of the carbon allotrope graphdiyene by direct deposition of radicals. Since halogenated precursors are too unstable, using trimethylsilyl as alternative leaving group will be evaluated.In the second part, heating in a noble-gas atmosphere instead of the usual vacuum conditions will be explored as a novel synthesis approach. The resulting increase of desorption temperatures enables reactions on surfaces that have failed thus far due to premature desorption of the educts. Two model reactions will be studied: (1) Melem condensation for the synthesis of carbon nitrides. After fundamental research on the reaction conditions, regular 2D polymers will be targeted by carrying out the reaction under reversible conditions. (2) Deprotonation of thiols on inert surfaces with the goal to synthesize disulfide-bridged 2D polymers. Thereby, dynamic covalent chemistry shall facilitate equilibration into regular structures.