The aim of my research was to investigate Ru(II) mixed ligand complexes through synthesis and characterisation and through the use of deuteriation. The location of the excited state in the dinuclear species was to be determined through use of selective deuteriation of ligands. Acid/ base dependency o f these 1,2,4-triazolecontaining complexes may be applied in the area of supramolecular chemistry due to its switch on/off effect. However to arrive at this stage a series of studies were necessary. In chapter 3, reveals the description of the synthesis of the starting material [Ru(L)2Cl2].2H2O, where L is bipyridyl, phenanthroline and biquinoline. This is followed by the deuteriation of these ligands (bpy, phen and biq) and the Hpytr and Hpztr ligands. The starting materials with the deuteriated ligands dg-bpy, dg-phen and di2-biq where consequently prepared .The synthesis and characterisation of the ligands 3-(pyridin-2-yl)-l,2,4-triazole, Hpytr and 3-(pyrazin-2-yl)-l,2,4-triazole, Hpztr and their complexes are shown in chapter 3. The use of deuteriation in the location of the excited state of the pztr' complexes was not as facile as first thought as the complex was found to have dual emitting properties due to close-lying excited states. New developments arose in the isolation of the stereoisomers of the pytr' and pztr complexes in collaboration with Dr. C. Villani, University of Rome, also a new concept of 99R u NMR was investigated of the pytr' and pztr isomers in collaboration with Prof. C. Elsevier, University of Amsterdam. Chapter 4 is the investigation of complexes containing the ligand 3-(pyrazin-2-yl)-5- (pyridin-2-yl)-l,2,4-triazole, Hppt. This ligand was synthesised and also deuteriated to prepare selectively deuteriated complexes as in chapter 3 with the same starting materials. The synthesis and characterisation was described in this chapter for these complexes and y9Ru NMR was obtained. Also a crystal structure of the N2 of the triazole ring to the pyrazine isomer of the ppf complex was achieved. Chapter 5 is the conclusive chapter of this text, which describes the synthesis of the dinuclear complexes of the ppf ligand, and this is prepared via two routes the indirect and the direct route. The indirect route is prepared using the isolated isomers of the monomers. The characterisation and selective deuteriation is discussed. From the redox and photophysical behaviour of the dinuclear complexes some theories were derived. Chapter 6 is conclusions and future work, which sums up the results o f this thesis and the consequential studies, which have evolved.