A joint experimental and theoretical work to explain the electronic and geometrical structure of an in situ prepared film of iron phthalocyanine (FePc) on silicon (100) is presented. FePc molecular films have been characterized by core and valence photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS), and the results have been interpreted and simulated by density functional theory (DFT) calculations. C1s and N1s PE spectra have been analyzed by taking into account all chemically nonequivalent C and N atoms in the molecule. In the Fe2p(32) spectra it has been possible to resolve two components that can be related to the open shell structure of the molecule. By valence PES and N1s XAS data, the geometrical orientation of the FePc molecules in the film could be determined. Our results indicate that for the FePc on Si(100), the molecules within the film are mainly standing on the surface. The experimental N1s XAS spectra are very well reproduced by the theoretical calculations, which are both angle and atomic resolved, giving a detailed description of the electronic and geometric structure of the FePc film. Furthermore, the asymmetry and the intensity angle variation of the first N1s XAS threshold feature could be explained by the presented DFT calculations as due to the chemical nonequivalence of the N atoms and the symmetry character of the lowest unoccupied molecular orbital.

The electronic structure of a vapor-sublimated thin film of metal-free phthalocyanine (H2Pc) is studied experimentally and theoretically. An atom-specific picture of the occupied and unoccupied electronic states is obtained using x-ray-absorption spectroscopy (XAS), core- and valence-level x-ray photoelectron spectroscopy (XPS), and density-functional theory (DFT) calculations. The DFT calculations allow for an identification of the contributions from individual nitrogen atoms to the experimental N1s XAS and valence XPS spectra. This comprehensive study of metal-free phthalocyanine is relevant for the application of such molecules in molecular electronics and provides a solid foundation for identifying modifications in the electronic structure induced by various substituent groups.

Phthalocyanines (Pcs) are capable of converting sunlight into electric energy when adsorbed on TiO 2 in a dye-sensitized solar cell. Of special interest in this type of cell is the energy level alignment as well as how molecules adsorb on the surface as it determines the output of the cell. We investigated the FePc-TiO 2 (110) interface using scanning tunneling microscopy, synchrotron-based photoelectron spectroscopy, and X-ray absorption spectroscopy. We found a strong coupling of the first-layer FePc to the substrate resulting in an alteration of the electronic structure and charge transfer from the molecules. The FePc in the second layer is not severely affected by the bonding to the surface and has bulk-like electronic properties. The growth of FePc thin films proceeds in a layer plus island mode, and the molecular plane is parallel to the surface. The energy level alignment at the interface is determined, and the lowest unoccupied molecular orbital is found above the conduction band minimum of the oxide substrate.

Resonant core spectroscopies are applied to a study of the excited electron transfer dynamics on a low-femtosecond time scale in systems of aromatic molecules ͑isonicotinic acid and bi-isonicotinic acid͒ adsorbed on a rutile TiO 2 (110) semiconductor surface. Depending on which adsorbate state is excited, the electron is either localized on the adsorbate in an excitonic effect, or delocalizes rapidly into the substrate in less than 5 fs ͑3f s ͒ for isonicotinic acid ͑bi-isonicotinic acid͒. The results are obtained by the application of a variant of resonant photoemission spectroscopy.

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