Magnus Borgström

Synthesis and properties of an iron hydrogenase active site model linked to a ruthenium tris-bipyridine photosensitizer

This thesis describes the synthesis and properties of ruthenium complexes relevant to artificial photosynthesis. The work includes preparation of RuIIpolypyridine complexes as well as multi component systems where RuII(bpy)3 or RuII(tpy)2 type complexes are used as photosesnsitizers.In the first part, the synthesis and characterisation of bipyridyl(pyridyl)methane type ligands and the corresponding ruthenium(II) bistridentate polypyridyl complexes is described. The bipyridyl-pyridyl methane type ligands were designed to increase the excited state lifetime of ruthenium(II) bisterpyridine-type complexes by altering the ligand field as compared to normal terpyridine ligands.In the second part photoinduced electron transfer and formation of charge separated states in donor-photosensitizer dyads or donor-photosensitizer-acceptor triads is studied. The first covalently linked donor-photosensitizer-acceptor triad with tyrosine as electron donor was prepared, and long lived light induced charge separation was observed. RuIIterpyridine complexes linked to carotenoid or tyrosine were also prepared, for studies of light induced charge separation on a TiO2 surface. Tryptofan was covalently linked to Ru(bpy)3 and proton coupled electron transfer from tryptophan to photogenerated ruthenium(III) was demonstrated. A pH-dependent study of the electron transfer rate gave insight into the mechanism of proton coupled electron transfer in amino acids.Finally, the last part of the thesis presents the preparation and properties of the first complex containing a photosensitizer covalently linked to a Fe-hydrogenase active site model.

Distance-independent photoinduced energy transfer over 1.1 to 2.3 nm in ruthenium trisbipyridine–fullerene assemblies

Ruthenium trisbipyridine C60 dyads linked viapara-phenyleneethynylene units have been prepared. They displayed a rapid energy transfer from Ru to C60 with a rate that was independent of distance, from 1.1 to 2.3 nm. The results are explained by a hopping mechanism involving a bridge-localized excited-state. In fact, for the longest bridge this state was lower in energy than the Ru-based MLCT state, as evidenced by the spectroscopic data.

Intramolecular charge separation in a hydrogen bonded tyrosine–ruthenium(II)–naphthalene diimide triad

Long-lived charge-separated states in the ns to [micro sign]s range were observed upon laser flash excitation of a donor-chromophore-acceptor triad based on tris(bipyridine) ruthenium(ii) as photo-sensitizer, naphthalene diimide as acceptor, and a hydrogen bonded phenol as donor.