Dye-sensitized solar cells (DSCs) were designed by Michael Grätzel. They have become as a promising inexpensive alternative to light-current conversion. Basically, DSCs are constituted by nanocrystalline films of a semiconductor oxide, a layer of dye adsorbed to the oxide surface, solution of iodide/triiodide redox couple that by its reduction regenerates the dye after theelectron-injection to the semiconductor. Nowadays, continuous researches are being carried out because of the variety of elementary components present in these cells.The process of current generation starts with the photo-excitation of the dye molecules, being this, the most important topic that has attracted a considerable experimental and theoretical interest. Studies point to different kind of dyes that allow tuning the properties and then to optimize their overall performance in assembled devices.The dyes show interesting properties useful in the design of a DSC, namely light absorption in the UV-Visible region of the electromagnetic spectrum, chemical stability, sensitization, effective adsorption on the semiconductor surface, electron-separated states, etc. Among the wide amount of dyes employed, porphyrinic systems have shown to be efficient lightharvesting.In this sense, properties of different families constituted by monomers, dimers andtrimers of porphyrinic macrocycles coordinated to metals like Ti, Ni and Zn were studied. The structural modification consists in changing the peripheral β-substituents in the rings with the proposal to predict the geometrical and electronic properties of new complexes which can be good candidates as sensitizers in solar cells. In addition, the study of electron-injection mechanisms from dyes to a TiO2 nanoparticle was performed since a theoretical point of view.In general, the results show that complexes with electron donor peripheral substituents are very promising to provide good performances as sensitizers and they could act as light-harvesting for DSCs. On the other hand, it was found a theoretical tool which allows differentiation of the direct and indirect photo electron-injection mechanisms in a DSC.PFCHA-BecasDoctorado en Fisicoquímica Molecular105p.PFCHA-BecasTERMINADA