Iron and ruthenium compounds with low-lying ligand field excited states anchoring to titanium dioxide

The work presented in this thesis quantifies the excited state properties of iron(II) and ruthenium(II) compounds in fluid solution and when anchored to mesoporous thin films of nanocrystalline TiO2 particles. A brief overview of potential application in dye-sensitized solar cells and of spin crossover in iron(II) compounds is introduced in Chapter 1. In Chapter 2, thermally induced and light-induced spin crossover were characterized for a series of iron(II) tris-chelate compounds in fluid solution and on nanocrystalline TiO2 surfaces. The high spin to low spin relaxation process displayed a first order kinetics in solution and a distribution analysis was used to quantify the same behavior on the metal-oxide surfaces. Chapter 3 reports the photophysical properties of ruthenium compounds coordinated with diazafluorenone and related ligands. Comparative studies in solution and on TiO2 surfaces were investigated as well as the effects of surface pretreatments with aqueous acid or base solution. Evidence for a ring opening reaction for a ruthenium-diazafluorenone compound on base-pretreated TiO2 film is presented. In Chapter 4, a series of ruthenium ammine compounds with short lived lifetimes were used to sensitize nanocrystalline TiO2 thin films, and the excitation wavelength dependence of the electron injection efficiency was quantified. An unusual temperature-dependent spectroscopic absorbance is reported for a high spin iron(II) compound in fluid solution in Chapter 5.