Over the past two decades molecular design has played an important role to control, at the molecular level, the properties of the interface between nanostructured metal oxide semiconductors (particularly TiO₂ and ZnO) and chromophoric compounds, especially porphyrin derivatives, as these are efficient dyes for dye sensitized solar cells and effective photocatalysts. The ultimate objective is develop hybrid organic-inorganic systems that are efficient for solar energy conversion, but an important aspect of this research is the ability gain a fundamental understanding of charge transfer processes at these important interfaces. The presentation will address several aspect of porphyrin design that our group, in collaboration with others, has focused on and, in particular, our recent progress in the influence of interfacial dipoles built in the porphyrin framework.