Surface-orientation- and ligand-dependent quenching of the spin magnetic moment of Co porphyrins adsorbed on Cu substrates

Abstract

The magnetism of adsorbed Co porphyrin molecules is controlled by their ligands and the substrate's orientation.

Reversible redox reactions in metal-supported porphyrin: the role of spin and oxidation state

“…22 Indeed, the Co(I)-porphyrin systems supported by silver and copper surfaces show null or very week XMCD signal. 22,23 The Co(I) supported by Ag(111) enables the binding of nitric oxide (NO) at 140 K, weakening the Co-Ag interaction because of the surface trans-effect. 4,24,25 In this communication, we examine more deeply the axial ligand binding of NO 2 to a CoTPP network grown on bare and oxygen-modified Cu(100), disentangling the relation between oxidation and spin state of the metal ion, as well as elucidating the electronic configuration that promotes the reaction with the gaseous species.…”

Insight into intramolecular chemical structure modifications by on-surface reaction using photoemission tomography

“…Together with the surface-driven conformational changes, the porphyrin molecules may undergo on-surface temperatureinduced chemical changes of their molecular structure. [2][3][4][5][6] A well-known surface-assisted ring-closure reaction in the case of metal-OEP involves the peripheral ethyl groups and results in the transformation of the OEP in tetrabenzoporphyrin (TBP), which occurs via the dehydrogenation of two neighbouring ethyl groups, followed by the formation of six-membered carbon rings (see Fig. 1).…”

“…5 In contrast to this system, CoOEP on Cu(100) has shown a sizable magnetic moment, while CoTBP displayed a quenched moment on this substrate. 4 Notably, the manipulation of the magnetic anisotropy in metal porphyrin molecules induced by ringclosure reactions is a key issue for the development of molecular-based spintronic devices.…”

“…16 In the present work, we will show that the PT approach can also be extended to the study of surfaceinduced intramolecular modifications, i.e., ring-closure reaction, in single molecules self-assembled in molecular arrays. More frequently, intramolecular reactions are monitored by STM, temperature-programmed desorption (TPD), X-ray photoemission spectroscopy (XPS) and NEXAFS techniques, [2][3][4][5][6]17,18 which do not always allow the authoritative identification of an adsorbed species. Only indirect conclusions can be made from, e.g., the presence or absence of specific vibrational modes in infrared spectroscopy or chemical shifts in core-level spectroscopy.…”

“…4 Following the XMCD measurements and theoretical calculations reported in ref. 4, and the XPS and NEXAFS measurements shown here, we propose that the charge transfer at the organic/metal interface stabilizes the cobalt ion in CoOEP and CoTBP on Ag(100) in a non-integer valence state, with a formal oxidation state between +1 and +2.…”