Energy level alignment of a zinc(II) tetraphenylporphyrin dye adsorbed onto TiO₂(110) and ZnO(112̄0) surfaces

The electronic structure of the Zn(II)-5-(3,5-dicarboxyphenyl)-10,15,20- triphenylporphyrin dye (ZnTPP-Ipa), chemisorbed onto ZnO(112̄0) and TiO₂(110) single-crystal surfaces, has been investigated by means of density functional theory (DFT) and by electron spectroscopy methods in an ultra-high-vacuum environment. The core levels (Ti 2p and Zn 2p) as well as the valence band have been probed using X-ray and ultraviolet photoemission spectroscopies, whereas the conduction band has been evaluated from inverse photoemission spectroscopy. The calculated density of states for the gas phase molecule compares well to the experimentally determined electronic structure, allowing both a simple understanding of the adsorbate electronic properties and a direct determination of the ZnTPP-Ipa frontier orbitals with respect to the substrates' band edges.