Tuning Transition Metal‐Containing Molecular Magnets by On‐Surface Polymerization

Porphyrins are promising multifunctional units particularly interesting for the realization of molecular nanodevices. Their structural variety allows to create precursors suitable for the on-surface polymerization of porphyrin blocks. The corresponding increased stability and improved transport properties of the formed polymerized molecular nanostructures make them practically worthwhile. For the case of 2D porphyrin materials, the effect of polymerization on the magnetic properties of transition metal ions has not been reported yet. Therefore, details on the properties of an extended covalent nickel tetraphenylporphyrin network formed via Ullmann coupling on the Cu(111) surface are reported. By using photoelectron and absorption spectroscopies together with density functional theory calculations, it is systematically evolving how the functional properties of the Ni centers are changed within a polymerized molecular structure in comparison to single-molecule nickel tetraphenylporphyrin derivatives that build the 2D molecular network. A model that explains the differences in the electronic and magnetic properties observed for the Ni centers in both structures based on the additional rigidity characteristic of the molecular layer after polymerization is drawn.