Role of redox-active axial ligands of metal porphyrins adsorbed at solid-liquid interfaces in a liquid-STM setup

Thomas Habets; Sylvia Speller; Johannes A A W Elemans

doi:10.3762/bjnano.11.110

Role of redox-active axial ligands of metal porphyrins adsorbed at solid-liquid interfaces in a liquid-STM setup

Beilstein J Nanotechnol. 2020 Aug 24:11:1264-1271. doi: 10.3762/bjnano.11.110. eCollection 2020.

Authors

Thomas Habets¹, Sylvia Speller^{2

3}, Johannes A A W Elemans¹

Affiliations

¹ Radboud University, Institute for Molecules and Materials (IMM), 6525 AJ Nijmegen, Netherlands.
² University of Rostock, Institute of Physics, Albert-Einstein-Straße 23, 18059 Rostock, Germany.
³ University of Rostock, Department Life, Light, Matter, Albert-Einstein-Straße 25, 18059 Rostock, Germany.

Abstract

In a liquid-STM setup environment, the redox behavior of manganese porphyrins was studied at various solid-liquid interfaces. In the presence of a solution of Mn(III)Cl porphyrins in 1-phenyloctane, which was placed at a conductive surface, large and constant additional currents relative to a set tunneling current were observed, which varied with the magnitude of the applied bias voltage. These currents occurred regardless of the type of surface (HOPG or Au(111)) or tip material (PtIr, Au or W). The additional currents were ascribed to the occurrence of redox reactions in which chloride is oxidized to chlorine and the Mn(III) center of the porphyrin moiety is reduced to Mn(II). The resulting Mn(II) porphyrin products were identified by UV-vis analysis of the liquid phase. For solutions of Mn(III) porphyrins with non-redox active acetate instead of chloride axial ligands, the currents remained absent.

Keywords: manganese; porphyrins; redox reactions; scanning tunneling microscopy; solid–liquid interface.

Grants and funding

We acknowledge funding by the Council for the Chemical Sciences of the Netherlands Organisation for Scientific Research (ECHO grant 700.57.023 and VIDI grant 700.58.423) and the European Research Council (ERC Starting Grant NANOCAT–259064). S.S. acknowledges the collaborative research center 1270 of the German Physical Society.