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Supramolecular organisation, conformation and electronic properties of porphyrin molecules on metal substrates Weber, Alexander

Abstract

The investigation and control of molecular properties is currently a dynamic research field. Here I present molecular level studies of porphyrin molecules adsorbed on metal surfaces via Low Temperature Scanning Tunneling Microscopy/Spectroscopy (STM/STS), supported by complementary X-ray absorption experiments. Intermolecular and molecule-surface interactions of tetrapyrdil porphyrin (TPyP) on Ag(111) and Cu(111) were investigated. TPyP self-assembles on Ag(111) over a wide sample temperature range into large, highly-ordered 2D chiral domains. By contrast, adsorption of TPyP on the more reactive Cu(111) leads to temperature dependent assemblies, governed decisively by the strong substrate influence. The increased metal-surface interactions on Cu(111) are accompanied by a conformational distortion of the porphyrin macrocycle. The TPyP’s pyridil groups were coordinated with single iron molecules, forming metal-organic complexes. Furthermore, the porphyrin’s macrocycle was metalated by exposing a layer of well-ordered TPyP to an iron atom beam, demonstrating a novel approach towards the fabrication of metallo-tetraaryl porphyrins performed in two dimensions under ultrahigh vacuum conditions. This method was similarly used to form lanthanideporphyrinates by coordinating tetraphenyl porphyrin (TPP) macrocycles with cerium. The influence of the metal center on the porphyrins’ electronic structure was investigated via STS for TPP, TPyP,Fe−TPyP, Fe−TPP, Ce−TPP, and Co−TPP, whereby the inhomogenous electron density distribution associated with individual frontier orbitals were imaged via dI/dV mapping. The symmetry and form of the molecular orbitals could be directly correlated to the saddle-shaped conformational adaptation for the case of Co −TPP.

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