The synthesis, spectroscopic and electrochemical characterisation of ruthenium (II) polypyridyl mononuclear and dinuclear complexes o f a 5-(2-pyridyl)-l,2,4-triazole ligand containing a catechol moiety are described. Chapter one is an introduction relevant to the work described in the thesis. The methods of characterisation, which are described in chapter two, include High Performance Liquid Chromatography, 'H-NMR, UV/Visible spectroscopy, fluorimetry, electrochemistry, spectroelectrochemistry, in ass spectrometry, X-Ray crystallography and lifetime emission measurements. Chapter three, describes the synthesis o f the mononuclear ruthenium (II) complexes of the protected catechol ligand 3-(r,2'-dim ethoxyphenyl)-5-(pyridin-2-yl)-l,2,4-triazole. The protected catechol moiety results in coordination of the Ru(Lx)2 (where Lx is bpy, dgbpy, phen, d8-phen or dcbpy) via N1 of the triazole and N1 of the pyridyl ring, which is confirmed by X-Ray crystallography. The synthesis of deuteriated complexes, is of significant benefit for the purposes of structural elucidation. Examination of the acidbase chemistry of the complexes by UV/Visible spectroscopy reveals information about the location of the excited state. The excited state of all the complexes is located on Lx. Electrochemical studies show a reversible metal centred Run/Rum couple. Evidence of irreversible oxidation of the dimethoxy moieties is observed at more anodic potentials. Chapter four describes the deprotection of the Ru(Lx)2 complexes o f 3 -(l',2 '- dimethoxyphenyl)-5-(pyridin-2-yl)-l,2,4-triazole forming complexes with a peripheral catechol binding site. These catechol complexes are precursors for the synthesis of dinuclear ruthenium complexes bound through the catechol binding site, the subject of chapter five, and for complexation of various other transition metals such as Fe(II), Fe(III) and Cu(II), the subject of chapter six. The electrochemical studies of the complexes in chapter four are complicated in comparison to their protected analogues. The oxidation of the catechol ligand precedes that of the metal centre and is quasireversible. Pretreatment of the glassy carbon electrode was necessary to resolve the processes due to adsorption of oxidised species onto the surface of the electrode. Attachment of the catechol complexes to nanocrystalline T i0 2 films indicates incident photon-to-current efficiency (IPCE) of greater than 30%. Chapter five describes the synthesis o f the dinuclear complexes o f 3 -(l',2 '- dihydroxyphenyl)-5-(pyridin-2-yl)-l,2,4-triazole from the mononuclear complexes discussed in chapter four. Semipreparative HPLC was required for purification and the dinuclear complexes were isolated in the semiquinone form. The complexes were characterised by mass spectrometry, HPLC and elemental analysis. Electrochemical analysis shows a reversible one-electron process for the hq/sq process and quasi reversible one electron processes for the sq/q and for the metal centre bound via the triazole. The second metal centre is not accessible with the conditions used. The complexes exhibit weak emission at neutral conditions. Finally chapter six explores the complexation of the mononuclear catechol complexes with various transition metals by titration of the catechol complexes with known molar equilavents of the metal. The stability constants and stoichiometry were estimated by attention to changes in the UV/VIS and emission spectra. The most interesting results were achieved with Fe(II), Fe(III) and Cu(II).