Building blocks for molecular devices: Organic molecules on the MgO (001) surface

The interaction of hydrocarbon and basic polar organic molecules with the MgO (001) surface has been theoretically studied using an embedded cluster model and hybrid density functional. It is found that both methane and benzene molecules do not bind strongly with the perfect surface and will not be deprotonated. Polar organic groups interact more strongly with the surface, with nitromethane and pyridine providing the largest binding energies (0.37 and 0.75 eV, respectively); however, in each case the molecules are physisorbed and not strongly polarized by the surface. The interaction of benzene and the larger aromatic hydrocarbon molecules, naphthalene and pyrene, with a single oxygen vacancy (F center) in neutral, +1, and +2 charge states is investigated. The +2 charged vacancy increases the binding energy of the molecules to the surface; however, there is no charge transfer to or from the vacancy in any of the states. It is found that the charged vacancies can significantly affect the electronic energy levels of the molecule and that the +2 vacancy can lower both the HOMO and LUMO levels of the molecule by approximately 3 eV. These calculations have importance for the design and control of molecular structure and energy levels in single-molecule electronic devices. © 2007 American Chemical Society