Berlin 2024 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 87: Focus Session: Molecular Nanostructures on Surfaces: On-Surface Synthesis and Single-Molecule Manipulation III

O 87.11: Vortrag

Donnerstag, 21. März 2024, 17:45–18:00, HE 101

On-Surface Reaction of Tetraphenylporphyrin with Caesium — •Leonard Neuhaus, Florian Münster, Kassandra Zoltner, Lukas Heuplick, Jan Herritsch, and J. Michael Gottfried — Department of Chemistry, University of Marburg, 35043 Marburg, Germany

Tetrapyrroles such as porphyrins and their metal complexes play important roles in living organisms and in modern technologies, e.g., in energy storage, (electro-)catalysis and sensor systems. While transition metal complexes of tetrapyrroles on surfaces have been well studied in the last decades, much less is known about their complexes with alkali metals. Here, we report studies of the reaction of tetraphenylporphyrin (H2TPP) with vapor-deposited caesium in the multilayer and (sub)monolayer regimes on Ag(111). XPS indicates for the submonolayer and multilayer partial metalation to Cs2TPP already at 300 K, whereas in monolayer regime no reaction is observed at this temperature. STM however, shows that the Cs atoms still coordinate to the porphyrin molecules at 300 K. After annealing to 400 K full conversion is observed. DFT calculations suggest that the Cs2TPP complex has a bipyramidal structure with Cs ions on both sides of the molecular plane, which is in line with STM measurements. In complementary temperature-programmed reaction (TPR) experiments, the desorbing species were clearly identified by mass spectrometry as Cs2TPP. TPR also indicates that Cs2TPP is thermally stable up to at least 700 K.

Keywords: Alkali Metals; Porphyrin; Metalation; XPS; TPD