In the present study, an extensive investigation of the molecule-surface interaction in hybrid systems formed by phthalocyanines (Pcs) and inorganic semiconductors (IS) has been performed by using ab initio theoretical methods. The aim of this study is to provide a framework to design effectively coupled Pcs/IS systems, assumed here to be characterized by the formation of chemical bonds between the two components and by a molecule-surface charge-transfer involving the π-electron clouds responsible of the Pc optical and transport properties. The achieved results
strengthen a crucial point for designing coupled Pc/IS structures, that is, the occurrence of a universal alignment of the Pc electronic levels with respect to the semiconductor band structure, previously suggested only on the ground of a limited set of results. Present results also confirm that an effective organic-inorganic coupling can be achieved through a careful choice of the Pc-substrate system and the semiconductor doping. In this regard, they trace also novel routes for designing hybrid Pc/IS systems by showing that the degrees of freedom for reaching an effective coupling can be increased by modifying the molecular architecture. Finally, present results predict that X-ray photoelectron spectroscopy (XPS) measurements can give an experimental evidence of molecule-surface charge-transfer processes occurring in coupled Pc/IS systems.