Intramolecularly resolved Kondo resonance of high-spin Fe(II)-porphyrin adsorbed on Au(111)

Using cryogenic scanning tunneling microscopy, we measured the electronic states and Kondo resonance of single Fe(II)-porphyrin molecules adsorbed on a Au(111) surface with intramolecular resolution. We found that the Fe(II) ion introduces a spin-polarized molecular state near the Fermi level. Tunneling spectroscopy revealed that this state gives rise to Kondo resonance exhibiting characteristics different from those of the Fe(II) spin state. Spin-polarized density functional theory calculations revealed that the molecule was weakly adsorbed on the surface, yet still switches its spin configuration from S = 1 to 2. The spin switching was found to be driven by three effects: a structural distortion of the macrocyclic ring from planar to saddle shaped, a weak chemical bonding between the Fe and the Au surface atom underneath, and weakened Fe-N bonds due to Au(111)-molecule charge transfer.