Near- and far-field effects on molecular energy level alignment at an organic/electrode interface

We investigate the evolution of the interfacial electronic structure at the interface of (sub)monolayer vanadyl naphthalocyanine (VONc) on highly oriented pyrolytic graphite (HOPG). Both the vacuum level and molecular energy levels show a significant but fundamentally different dependence on coverage, resulting in an overall change of the ionization potential with coverage. We use a simple model to show how this effect arises from the differential sensitivity of these levels to the near- and far-field properties of the dipole-layer-generated interfacial electric potential. These results help to unravel the electronic structure at organic/electrode interfaces, with direct implications for organic electronic devices.