Orbital-Mediated Tunneling, Inelastic Electron Tunneling, and Electrochemical Potentials for Metal Phthalocyanine Thin Films

Orbital-mediated electron tunneling through both occupied and unoccupied orbitals of metal phthalocyanines imbedded in metal−insulator−metal tunnel junctions is reported and discussed in terms of transient oxidation and reduction of the molecular species. Electrochemical oxidation and reduction potentials for the solution phase molecular systems are compared to the orbital-mediated tunneling spectroscopy (OMTS) data and a strong correlation is observed. These results are consistent with a simple model. It is demonstrated that different redox sites and states within a given molecule within a thin film will shift in unique ways relative to the equivalent processes in solution. Inelastic scattering from phthalocyanine π−π* transitions and metal centered d−d transitions are also observed.