Toward Solar Energy Conversion into Fuels: Design and Synthesis of Ruthenium-Manganese Supramolecular Complexes to Mimic the Function of Photosystem Ⅱ

摘要

To mimic the electron donor side of Photosystem Ⅱ (PSII), a number of supramolecular model complexes have been designed and synthesized. Ruthenium(Ⅱ) tris-bipyridyl complexes have been used in most cases as photosensitizers, mimicking the function of P_(680) in PSII. As electron donors, monomeric and dimeric manganese complexes and tyrosine have been introduced into the supramolecular systems, modelling the Mn cluster and Tyrosinez respectively in PSII. For monomeric manganese complexes, di-, tri- and terra-dentate ligands have been linked to a Ruthenium(Ⅱ) tris-bipyridyl type complex; and for dimeric manganese complexes hepta-dentate ligands containing pyridines have been used. Some related ligands, where two pyridines have been replaced by phenolate groups have also been synthesized, in order to get ligands that can stabilize manganese complex in high valence states. Photophysical and photochemical studies showed that the electron transfer rate from monomeric Mn complex to photo-generated Ru(Ⅲ) was low when Mn-Ru distance was long, while the electron transfer rate was enhanced when the Mn-Ru distance was short. However, the excited state of ruthenium complex was quenched if Mn got close to the Ru, leading to a short lifetime. By synthetically inserting a tyrosine unit between Ru and Mn moieties, quenching of the excited state lifetime of Ru was reduced, and the electron transfer from Mn to Ru(Ⅲ) was very fast although the Mn-Ru distance was long. These supramolecular Ru-Mn systems are closely modelling the electron donor side of PSII both functionally and structurally. The design and synthesis of these model systems are summarized and discussed in this chapter.