title: Porphyrin Metalation at MgO Surfaces: A Spectroscopic and Quantum Mechanical Study on Complementary Model Systems.
abstract: We show that both single-crystalline and nanostructured MgO surfaces convert free-base tetraphenyl porphyrin (2HTPP) into magnesium tetraphenyl porphyrin (MgTPP) at room temperature. The reaction can be viewed as an ion exchange between the two aminic protons of the 2HTPP molecule with a Mg(2+) ion from the surface. The driving force for the reaction is the strong stability of the formed hydroxyl groups along the steps and at defects on the MgO surface. We have used an integrated characterization approach that includes UV/Vis diffuse reflectance measurements on nanostructured powders, X-ray photoelectron spectroscopic investigation of atomically clean MgO(100) single-crystalline thin films, and density functional theory (DFT) calculations on model systems. The DFT calculations demonstrate that MgTPP formation is strongly exothermic at the corners, edges and steps, but slightly endothermic on terrace sites. This agrees well with the UV/Vis diffuse reflectance, which upon adsorption of 2HTPP shows a decrease in the absorption band associated with corner and edge sites on MgO nanocube powders.
authors.affiliation: Department of Chemistry & Physics of Materials, Paris-Lodron University Salzburg, Salzburg, Austria.
authors.forename: Johannes
authors.initials: J
authors.lastname: Schneider
authors.affiliation: Institute of Physical Chemistry II, Friedrich-Alexander-University Erlangen-Nürnberg, Erlangen, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Franke
authors.affiliation: Interdisciplinary Center for Molecular Materials (ICMM) and Computer-Chemistry-Center (CCC), Friedrich-Alexander-University Erlangen-Nürnberg, Erlangen, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Gurrath
authors.affiliation: Institute of Physical Chemistry II, Friedrich-Alexander-University Erlangen-Nürnberg, Erlangen, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Röckert
authors.affiliation: Department of Chemistry & Physics of Materials, Paris-Lodron University Salzburg, Salzburg, Austria.
authors.forename: Thomas
authors.initials: T
authors.lastname: Berger
authors.affiliation: University Service Centre for Transmission Electron Microscopy, Vienna University of Technology, Vienna, Austria.
authors.forename: Johannes
authors.initials: J
authors.lastname: Bernardi
authors.affiliation: Interdisciplinary Center for Molecular Materials (ICMM) and Computer-Chemistry-Center (CCC), Friedrich-Alexander-University Erlangen-Nürnberg, Erlangen, Germany. bernd.meyer@chemie.uni-erlangen.de.
authors.forename: Bernd
authors.initials: B
authors.lastname: Meyer
authors.affiliation: Institute of Physical Chemistry II, Friedrich-Alexander-University Erlangen-Nürnberg, Erlangen, Germany.
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Steinrück
authors.affiliation: Institute of Physical Chemistry II, Friedrich-Alexander-University Erlangen-Nürnberg, Erlangen, Germany. ole.lytken@chemie.uni-erlangen.de.
authors.forename: Ole
authors.initials: O
authors.lastname: Lytken
authors.affiliation: Department of Chemistry & Physics of Materials, Paris-Lodron University Salzburg, Salzburg, Austria. oliver.diwald@sbg.ac.at.
authors.forename: Oliver
authors.initials: O
authors.lastname: Diwald
keywords: ion exchange; metalation; nanocubes; porphyrin; surface defects