Ruthenium (II) polypyridyl complexes as models for artificial photosynthesis: synthesis and characterisation

This thesis presents a study on the synthesis and characterisation of a series of novel ruthenium (II) polypyridyl complexes, which are potentially models for artificial photosynthesis. Chapter 1, the introduction, highlights the literature relevant to the topic. In Chapter 2, the experimental conditions of the various methods of characterisation are described. The synthesis and characterisation of a range of novel 5-phenyI-3-(2- pyridyl)-1,2,4-triazoles, their Ru(bpy)2 and their Ru(dg-bpy)2 complexes are discussed in Chapter 3. Each of the new ligands bear terminal functional groups which allow larger supramolecular systems to be constructed. Complexes were characterised by spectroscopic (NMR, UV/Vis, Luminescence) and electrochemical techniques. Their properties were found to be pH dependent. In every case, the emissive excited state of the ruthenium complexes was determined to be located on the bpy ligands. Chapter 4 is concerned with the synthesis and characterisation of the Ru(bpy)2 and Ru(dg-bpy)2 complexes of novel 5-phenyl-3-(2-pyrazyl)-l ,2,4-triazoles, analogous to those described in Chapter 3. The presence of the strongly ^-accepting pyrazine alters the electronic properties, with respect to the pyridyl triazole complexes. Again, spectroscopic and electrochemical studies display a strong pH dependency. The location of the excited state was pH dependent, with it being bpy-based above pH 4, while below this pH, results were inconclusive. In Chapter 5, the complexes prepared in Chapters 3 and 4 are used to prepare more complex systems. In collaboration with Prof. Akkermark in Sweden, two tyrosine containing complexes were prepared, as models of the tyrosine Yz, which is located between Peso and the manganese cluster in Photosystem II. A range of ruthenium complexes containing potential manganese chelating ligands were also prepared. Due to chromatographic problems, it was not possible to isolate them in a pure form. In collaboration with Prof. Girerd in Paris, a Ru-Tyr-Mn2 system was prepared and characterised. The manganese atoms were found to be antiferromagnetically coupled, giving rise to similar EPR and magnetic susceptibility measurements to a known model manganese complex. The work presented in Chapter 6 was carried out in collaboration with Prof. Fuhrhop in Berlin, where a novel bola amphiphile was prepared. It is hoped that this may be used to prepare a rigid membrane containing Angstrom gaps, which may be closed by complexation with ruthenium. The ruthenium complexes of the interemediates were also prepared and characterised by spectroscopic and electrochemcial techniques. Finally, Chapter 7 gives an overview of the work that is presented in this thesis and suggests further experiments, which may be carried out in future studies