This thesis describes the development of a new single-step method for the deuteriation of polypyridyl ligands and the possible applications of those deuteriated ligands. Chapter 1 gives a summary of some of the deuteriation methods used previously and describes how ligand deuteriation may be used as a tool for the study of the excited states of Ru(II)polypyridyl ligands. Chapter 3 details the optimisation of the new deuteriation method to the synthesis of deuteriated 2,2’-bipyridyl (bpy), temperature and time variation studies revealed that the optimum reaction conditions for the synthesis of bpy-d8 were 3 days at 200°C, using 0.25g Pd/C per 3g bpy, the bpy deuteriated in this manner was calculated to be 95% deuteriated, it was also found that complete deuteriation may be obtained by repeating the procedure once with fresh D20 and Pd/C. In this chapter we also see that the deuteriation method reported was successfuly applied to a whole range of (never previously deuteriated) pyridyl- and pyrazyl- triazole ligands. The temperature variation studies carried out on bpy indicated that it should be possible to achieve selective deuteration of bpy by carrying out the experiment with shorter reaction times, at lower temperatures and using less Pd/C. These milder conditions may also allow the deuteration of those compounds for which the previous conditions had proved too severe, eg. 3-(2,5’-dimethoxy-phenyl)-5-(pyridin-2-yl)-l,2,4-triazole. Chapter 4 shows some examples of how deuteriated polypyridyl ligands can be used both to obtain valuable information on the excited states, and to simplify the 'Hnmr, of Ru(II)polypyridyl complexes.