Mapping the electronic structures of a metalloporphyrin molecule on Au(111) by scanning tunneling microscopy and spectroscopy

The intramolecular structure of a Co-porphyrin molecule adsorbed on Au(111) is studied using scanning tunneling microscopy and spectroscopy. As the energy is swept from -2 to +2 eV across Fermi level, the shape of the molecular image dramatically evolves from a two-lobed object to a shape with a bright center and, finally, to a four-lobed object. With the help of first-principles calculations, we explain these distinctive features in terms of the integrated molecular orbitals of a saddle conformation and the contribution of a Kondo state. Based on the molecular structure and the orbitals, we explain why the modification in the electronic states of the molecules by the presence of the substrate is relatively modest.