Strategien zur Entwicklung funktionalisierter Oberflächen auf Basis von Tetrapyrrolkomplexen - Porphyrine und Corrole an Metall/Organik-Grenzflächen

This thesis examines the relationship between structure and molecular properties of adsorbed porphyrins on coinage metal surfaces using surface-sensitive methods under ultra-high vacuum conditions. The employed experimental methods include photoelectron spectroscopy and near edge X ray absorption fine structure spectroscopy as well as scanning tunneling microscopy and low-energy electron diffraction. The experimental results are supported by quantum chemical calculations within the framework of density functional theory. The main focus of this thesis lies on the relationship between the size of the porphyrin mac-rocycle and the molecular properties as well as the interaction of an adsorbed porphyrin with the underlying substrate. The influence of the ring size is systematically investigated by comparing porphyrins and corroles. The latter contain a smaller macrocycle and act as trianionic ligands. On the basis of quantum chemical calculations of the parent porphin and corrole macrocycles, the fundamental properties of both molecules are discussed. In particular, the influence of the porphyrin ring contraction on the molecular structure, aromaticity, NH acidity, and electronical properties as well as the metal−ligand bond are investigated. Using monolayers of an alkyl sub-stituted free-base porphyrin and a similar corrole on the Au(111), Ag(111), and Cu(111) sur-face, the effect of the smaller ring size on the adsorbate interactions is studied experimentally. In case of the free-base corrole a surface-induced NH dehydrogenation and the formation of a radical is observed. As a result of an electron transfer emerging from the metal surface, the mol-ecule is reduced and the aromaticity is re-established. On Cu(111) the corrole is affected by an on-surface reaction with a copper adatom forming a copper corrole complex. The relationship between the central metal atom, the ligand structure, and the choice of the substrate material are investigated by a comparative study of cobalt porphyrin and corrole com-plexes as well as their nickel equivalents. The influence of the ring contraction on the met-al−ligand bond and the electronic state of the central atom as well as the role of the substrate are elucidated. On Ag(111), the smaller macrocycle of the cobalt corrole complex interacts more strongly with the metal substrate than the corresponding cobalt porphyrin complex. In case of the nickel porphyrin a reduction of the central atom is observed depending on the substrate used. On the relatively inert Au(111) surface the Ni2+ state is preserved upon adsorption, while the formation of a peculiar mixed-valence adsorbate structure occur on the more reactive Ag(111) surface. In this structure a certain fraction of the nickel atoms is reduced by an electron transfer from the metal surface to the porphyrin complex. The mixed-valence structure can be further modified by decreasing the overall molecular coverage or using a different substrate lat-tice. On the even more reactive Cu(111) surface all nickel centers are uniformly reduced. The studied nickel corrole complex exhibits a Ni2+ central atom. As a result, the ligand is formally oxidized. Thus, in the adsorbed molecule the Ni2+ state of the central atom is preserved and the corrole ligand is reduced depending on the substrate used. Thereby the ring size of the ligand’s macrocycle can be used to control whether an electron transfer from the substrate leads to a re-duction of the incorporated central atom or the ligand. Despite their interesting properties porphyrin and corrole complexes of s-block metals have not yet been studied extensively. Another major aspect of this thesis is to report on novel por-phyrin and corrole complexes of lithium, magnesium and calcium. Mass spectra are evaluated based on the isotopic signature of the molecular ion and possible fragments by using a self-developed software. In addition magnesium and calcium corrole complexes adsorbed on Au(111) and Ag(111) are investigated further. Moreover, the on-surface demetalation and transmetalation are investigated using a labile lead porphyrin complex. On Au(111) a demetalation of the porphyrin complex takes place while a tansmetalation was observed on Cu(111). Here, the central lead atom is exchanged by an adatom of the copper surface. This thesis also contains a contribution to the development of an electrospray ionization ion beam deposition device. In addition to an optimization of the quadrupoles and other construc-tional changes, a computer software was developed to read out various measuring instruments.