Interaction of Cobalt(II) Tetraarylporphyrins with a Ag(111) Surface Studied with Photoelectron Spectroscopy

The interaction of cobalt(II) tetraphenylporphyrin (CoTPP) and cobalt(II) tetrakis-(3,5-di-tert-butylphenyl)porphyrin (CoTTBPP) with a Ag(111) surface has been investigated with photoelectron spectroscopy (XPS/UPS). It is demonstrated that these adsorbed metal complexes are excellent model systems for studying the electronic interaction between a coordinated metal ion and a metal surface. The photoelectron spectra and work function data provide evidence that the electronic interaction between the cobalt ion and the silver surface results in a transfer of electron density from the surface to the ion. The presence of an additional electronic state located ∼1 eV above the singly occupied molecular orbital (SOMO) of the metalloporphyrins is consistent with a molecular orbital (MO) model of the Co−Ag interaction as is the fact that the energetic position of this state depends on the distance between the Co ion and the Ag surface. The adsorbate-induced work function changes for the saturated monolayers amount to −0.72 eV for CoTPP and −0.91 eV for CoTTBPP. For comparison, we also present data of monolayer films of tetraphenylporphyrin and zinc(II) tetraphenylporphyrin.