Structure-Function Relationships in RuII Complexes with Unconventional Ligands: Photophysical and Photochemical Studies

Abstract: The rich photophysics, photochemistry and electrochemistry of RuII complexes have attracted intense research interest in widely disparate fields. A large portion of the studied and applied complexes are derived from the archetypical [Ru(bpy)3]2+ (bpy is 2,2’-bipyridine), which absorbs in the visible region, displays a long lived (~1 μs), emissive metal-to-ligand charge transfer state, and shows reversible electrochemistry in both the ground and excited state. Adding substituents to the bpy ligand is a conventional way of fine-tuning the physical properties. Incorporating larger motifs, altering the coordination sphere geometry or coordinating ligands via other heteroatoms than nitrogen can result in substantially different physical properties. This latter approach is the subject of this thesis, and in it I have presented the results from studies on structure complexes incorporating what I chose to call unconventional ligands. This thesis is focused on the structure-function relationships in three series of RuII complexes: 1) With strained bpy-ligands, connected in the 3,3’-positions, with electron rich dithiol-motifs that display high light harvesting capabilities. Additionally, they promote hole-transfer when used for sensitizing a semiconductor substrate, with long-lived charge separated states. 2) Pyridine-thioether complexes that display excited state properties on par with [Ru(bpy)3]2+ and pyridine-sulfoxide complexes that display two-color reversible photo-isomerization in solution and immobilized on a semiconductor substrate. 3) Quinoline-pyrazole ligands that when coordinated form near perfect octahedral complexes; two of which display different selectivity toward photo-chlorination with respect to Cl--source, and one that displays room temperature dynamic diastereomerization in the ground state while at the same time being extremely photo-stable.