Reactive Aromatic Molecules on Metal Surfaces: Syntheses, Reactions and Structures
The interaction of organic molecules with metal contacts and the reactivity of those molecules are of high technological interest, especially in the field of organic electronics and surface-assisted catalysis. The presented work comprises the investigation of several reactive aromatic compounds on c...
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|Summary:||The interaction of organic molecules with metal contacts and the reactivity of those molecules are of high technological interest, especially in the field of organic electronics and surface-assisted catalysis. The presented work comprises the investigation of several reactive aromatic compounds on coinage metal surfaces. Although all systems raise their own scientific questions, all discussions concern either the on-surface synthesis, possible reactions or the formation of two-dimensional structures. In the studies, the methods of scanning tunneling microscopy (STM), X-ray and ultraviolet photoelectron spectroscopy (XPS, UPS) as well as near-edge X-ray absorption fine structure (NEXAFS) spectroscopy were employed. The experimental results are substantiated with insights from density functional theory (DFT) calculations.
The first experimental topic is focused on the structures and reactions of tetrapyrrole macrocycles on diverse surfaces. Corroles exhibit a slightly different chemical structure than porphyrins. In the investigations of hexaethyldimethylcorrole (3H-HEDMC) monolayers on Ag(111), an enhanced surface reactivity was observed. Furthermore, superstructures of 2H-HEDMC are formed at this temperature. The metalation of 3H-HEDMC with iron, cobalt and nickel was studied on Ag(111). The resulting organometallic complexes were investigated regarding the electronic state of the metal center. The investigation of tetraphenylporphyrin with co-adsorbed lead revealed a possible metalation and a transmetalation at increased temperatures. A bromine substituted nickel-tetraphenylporphyrin was studied concerning its reactive coupling and thus a resulting formation of covalent C–C bonds due to an Ullmann coupling.
The investigations on aromatic dicarbonitriles are dedicated to the influence of functional groups in reactively formed or self-assembled structures. An annulated naphthalenedicarbonitrile serves as precursor for the synthesis of an extended iron-naphthalocyanine. The precursor molecules self-assemble in locally ordered phases. The tetramerization was observed after post-deposition of iron onto a monolayer of the corresponding precursor and a subsequent annealing. While dicarbonitriles can be reactively linked in this fashion, the functional groups are also responsible for self-assembled nanostructures.
Large acenes are promising novel organic semiconductors, whose properties, e.g., the HOMO-LUMO gap or the reactivity, scale with the length of the annulated aromatic backbone. A diketone-bridged precursor was used in a surface-assisted synthesis of heptacene. The transition is achieved by thermal didecarbonylation. The precursor and heptacene molecules were furthermore investigated concerning the influence of the surface on the molecules.|
|Physical Description:||157 Pages|