The synthesis, electrochemical, spectroscopic, and photophysical characterisation of ruthenium(II) polypyridyl complexes containing quinone/hydroquinone moieties

The synthesis and characterisation of photophysical, electrochemical and photochemical properties of rulhenium(II) polypyridyl containing hydroquinone triazole or pyrazole moieties are described. The characterisations described involve, HPLC, ^Hnmr, UV/vis/NIR spectroscopy, fluorimetry, electrochemistry, spectroelectrochemistry, laser flash photolysis, and resonance Raman spectroscopy. In the main chapter of this thesis the investigation of a series of Ru(II) complexes bound to pyridyltriazole ligands bridged to pendent electroactive phenol, hydroquinone and quinone moieties is described. A novel synthesis for oxidation of the hydroquinone containing complex is described, employing benzeneselininc acid which, in a one pot reaction under very mild conditions, the hydroquinone may be completely oxidised without concomitant oxidation of the quinone. None of the complexes described exhibit intramolecular electron transfer from any of the electroactive groups under neutral conditions. This was associated with endoergonic AG values for intramolecular electron transfer in these complexes under neutral conditions. At high pH however, intramolecular electron transfer was observed in all complexes containing the electroctive aryl groups. This was associated with intramolecular hole transfer from the Ru(III)* to the phenolate, semiquinone or anionic hydroquinone formed from these ligands at high pH. This electron transfer is ranges around 2 x 10() s-1 in neutral acetonitrile, it is therefore rather a slow transfer, however, the resulting charge separated state is stable over several microseconds. The electron transfer processes also persist at cryogenic temperatures, and outside the glass phase are largely temperature independent. These complexes were therefore described as simple abiotic models for photosynthesis, this is particularly the case for the hydroquinone containing complex, which also exhibits an electrochemically induced intramolecular proton transfer verified by electrochemical and spectroelectrochemical measurements. In the second part of this thesis the synthesis and characterisation of mononuclear and dinuclear 0,N coordinated Ru(II) complexes to hydroquinonepyrazole and phenolpyridyltriazole were described. The mononuclear complexes exhibit intense, broad range, visible absorbances, with Xmax tailing to 800 nm, they are photostable, luminescent and electroactive. Luminescence in complexes bound via 0,N are normally rare. The dinuclear 0,N coordinated complexes produced stable mixed valence states. These mixed valence states exhibit class II behaviour, i.e. weakly coupled, electronic communication between the metal centres. This interaction is particularly weak in the complex bridged by the phenolpyridyltriazole, which shows an intervalence transition of unusually high energy. Most interestingly, this complex, which is luminescent in the (II)-(II) state exhibits increased luminescence in the mixed valence state, whereby it appeared that the unoxidised N,N coordinated side of this complex became isolated from the Ru(III)0,N side of the complex in the excited state. Finally, a novel synthesis for the deuteration of bipyridyl was described, this synthesis is a one pot, high yield reaction, that was considerably easier than that available in current literature. The properties of complexes containing deuterated bpy are described and the value of employing deuterat ion as a means of ascertaining the position of the LUMO was discussed