Ruthenium(II) Polypyridyl Complexes : Applications in Artificial Photosynthesis

Abstract: Molecular mimics of PS II, which consist of a photosensitizer linked to electron acceptors/donors, are attractive candidates for the conversion of solar energy into chemical energy. Several different classes of sensitizers have been studied and among these, ruthenium(II) polypyridyl complexes continue to attract major attention.The first part of this thesis presents the photophysical properties, stereochemistry, and general synthesis of ruthenium(II) polypyridyl complexes based on 2,2´-bipyridyl and 2,2´:6´,2´´-terpyridyl ligands. The second part deals with ruthenium(II) polypyridyl complexes linked to electron acceptors (benzoquinone, naphthalene diimide) and electron donors (phenothiazine, tyrosine, manganese complexes). Functionalized 2,2´-bipyridines and 2,2´:6´,2´´-terpyridines were synthesized and used in the stepwise assembly of the chromophore-quencher complexes. These were fully characterized and the redox properties were studied by cyclic and differential pulse voltammetry. The intramolecular charge-separated states formed after light excitation of the ruthenium(II) unit were observed by time-resolved absorption and EPR spectroscopy.In the third part of this thesis, the synthesis and photophysical properties of a novel class of bistridentate ruthenium(II) polypyridyl complexes based on bipyridyl-pyridyl methane ligamds are discussed. The solution structures of the homoleptic and heteroleptic complexes were studied by 2D NMR techniques. The X-ray structure of one of the homoleptic complexes has been solved. The effect on the excited state lifetime for these ruthenium(II) complexes compared to the parent [Ru(tpy)2]2+ is discussed. Finally, in one of the heteroleptic complexes an interesting reversible linkage iomerization was observed that could be induced either electrochemically or chemically.