Polypyridyl transition metal complexes with application in water oxidation catalysis and dye-sensitised solar cells

Abstract

This thesis contains complementary synthetic and computational studies of transition metal complexes with polypyridyl ligands for use either as water oxidation catalysts or for application in dye-sensitised solar cells (DSSCs). Chapter 1 introduces the reasons for researching water splitting catalysts and describes a number of current techniques used to do so; from photoelectrochemical cells to the use of transition metal polypyridyl complexes. It also introduces three commercially available types of solar cells; silicon, thin film and the dye-sensitised solar cell. Chapter 2 describes the synthesis of seven ruthenium(II) complexes with substituted 4'-(4-pyridyl)-2,2':6',2''-terpyridine ligands and their photophysical and electrochemical properties. Density Functional Theory (DFT) calculations were used to explore the compositions of the highest occupied- and lowest unoccupied molecular orbitals (HOMO and LUMO, respectively) and Time Dependent DFT (TD-DFT) was used to predict the absorption spectra of the complexes. Chapter 3 contains information on water soluble ruthenium(II) complexes, their synthesis, photophysical and electrochemical properties and their activity as water splitting co-catalysts. A mechanism to explain the variable activities of the complexes is also put forward. Chapter 4 describes the synthesis of two homoleptic Cu(I) complexes. One complex involves a simple 6,6'-dimethyl-2,2'-bipyridine ligand. The other complex contains a ligand with extended ?-conjugation. The properties of the Cu(I) complexes are studied in terms of their suitability for use in DSSCs. A strategy of ligand-exchange on the surface of titanium dioxide (TiO2) is then utilised to form surface-bound heteroleptic Cu(I) complexes and efficiences of these complexes in DSSCs were measured. Chapter 5 details the development of a suitable basis set to be used in both DFT and TD-DFT to predict the absorption spectra of the homoleptic Cu(I) complexes in Chapter 4; the accuracies of the predicted spectra are assessed. The properties of the uncharacterised, heteroleptic Cu(I) complexes were then predicted and the effects of the anchoring ligands on the overall properties of the complexes were assessed. Chapter 6 describes the synthesis of two mono-substituted bipyridine-based ligands and their corresponding homoleptic chiral copper(I) complexes. Variable temperature nuclear magnetic resonance (VT-NMR) experiments are described, along with the photophysical properties of the ligands and complexes. Chapter 7 consists of the overall conclusions and an outlook.