Observed and Theoretical Differences Between Ru(II) and Ir(III) Based Photosynthetizing Agents

Photosensitizing agents have been of interest for several decades due to their many catalytic applications. Photosensitizers capable of converting hydronium ions into hydrogen gas have recently become of particular interest as people look for renewable energy sources. Traditionally Ru(II) based complexes have been used for photoinduced hydrogen production, but some recent research indicates that Ir(III) based complexes may be better suited for this purpose. To explore the differences between Ru(II) and Ir(III) based complexes more thoroughly, [Ru(bpy)3] is compared to two other metal-ligand systems, [Ir(ppy)2(bpy)] and [Ir(ppy)2(phen)]. Molecular orbital theory in conjunction with redox and excited state data will be used to describe some of the reasons to expect reactivity differences between these compounds.