The study of the charge transfer reactions that take place at the different interfaces of Dye Sensitised Solar Cells (DSSC) shows that electron transfer reactions are very much optimised. However, there are recombination reactions between the oxidised dye and the photo-injected electrons, and between these electrons and the oxidised electrolyte, which result critical for the overall efficiency of the devices. Recently, it has been demonstrated that several dyes, which show poor light-to-energy conversion performance, increase the rate of electron recombination between the photo-injected electrons and the oxidised electrolyte when used as sensitizers. These dyes have in common the presence of extended π-conjugated systems that lie close to the semiconductor surface. Taking into account these observations, we have designed a series of heteroleptic Ruthenium (II) complexes where one of the 4,4’-dicarboxy, 2,2’-bipyridine ligands has been substituted by a phenanthroline moiety. Furthermore, the phenanthroline ligand has been modified with the introduction of electron donating or electron withdrawing groups to achieve the desired control over the molecular orbitals. Whilst electron-donating groups will increase the energy gap (HOMO-LUMO gap) the introduction of electron withdrawing groups will have the opposite effect. Our aim is to study and rationalise the possible effects over the interfacial charge transfer reactions, under working device conditions that the introduction in the dye of a more conjugated ligand, such as a phenanthroline, and its functionalization will have on the overall device efficiency.