Tuning the Magnetic Coupling of a Porphyrin with the Substrate through the Intramolecular Cyclization Reaction

One of the primary objectives in molecular nano-spintronics is to manipulate the electronic configurations of organic molecules with a d-electron center by suitable external means. Here, we demonstrate the tuning of the electronic configuration of tetrakis(pentafluorophenyl)porphyrin (FeF_20TPP) molecules on the Au(111) surface through a thermally induced intramolecular quadrauplicate cyclization reaction. During the reaction, the electronic configuration of a FeF_20TPP molecule on the Au(111) surface changes from (d_z^2^1d_\pi ^3) to (d_z^2^2d_\pi ^2). We attribute this change to significant difference in the adsorption height and variations in coupling between the orbitals of central metal atoms and the Au(111) surface. To further validate this mechanism, we substituted the central Fe ion with a Mn ion, predicting that an electronic configuration transition would not occur in MnF_20TPP and its product. Low-temperature scanning tunneling microscopy (STM) revealed that the FeF_20TPP on Au(111) exhibits no Kondo resonance, while its cyclization product exhibits Kondo dip near the Fermi level (E_\rm F). In contrast, both the MnF_20TPP and its product show pronounced Kondo dip at E_\rm F. Our work marks a significant step forward in controlling molecular electronic configuration through on-surface chemical reactions, paving the way for advanced molecular spintronics.