In this work, electronic structure calculations were performed on some polypyridyl ruthenium complexes to investigate their photophysical and photochemical properties. Two different topics are discussed : the S → O linkage photoisomerization of sulfoxide ligands and the photodissociation of thioether ligands in polypyridyl ruthenium complexes. We found some interesting results on the photoisomerization reaction mechanism by exploring the potential energy surface of the lowest triplet excited state for the following complexes, [Ru(bpy)2OSO]2+ and [Ru(bpy)2(DMSO)2]2+. We showed that the 3MC states populated during the photoisomerization process allow the elongation of the Ru-S bond and the isomerization of the sulfoxyde moiety. Furthermore, these states are responsible for the non-radiative deactivation of the excited state. The investigation of the Hmte ligand photodissociation in a series of [Ru(tpy)(L-L)Hmte]2+ complexes where L-L are ligands having different steric demands, highlighted that the 3MC states are strongly stabilized with respect of 3MLCT states for the most sterically hindered ligands.
