This thesis involves the characterisation of Ru(II) polypyridyl complexes when covalently linked to proteins and a study of their propensity to monitor conformational variances which these proteins undergo in solution. In the first section of this thesis, the Ru(II) complexes are covalently bound to various synthetic and natural proteins via selected binding sites on the biomolecules, and these protein-bound labels are extensively characterised via the spectroscopic and luminescent properties of the labels. Thereafter, these proteinbound labels are employed as spectroscopic probes of the conformational changes which the bound proteins undergo in solution via variations in the photophysical properties of these labels found to accompany structural changes of the proteins. Although the emission spectra of the labels are somewhat sensitive to the conformational properties of the bound protein, the decay lifetimes were found to be the most sensitive reporter, due to their sensitivity to their local environment. The a-helix to random coil transition of poly-amino acids were thereby probed by changes in the decay lifetimes of the labels. This section also investigates the potential of the decay lifetime of the labels as a probe of the unfolding process of natural proteins. Investigations into the effects of a number of parameters (i.e. label type and position on protein, temperature, chemical denaturants) on the probing potential of the labels were carried out. The final section involves the labelling of an enzyme with the same Ru(II) complexes. Firstly, the effect of the labelling on the activity of the enzyme was studied to determine the effect of such modification on the natural conformational properties of the enzyme. Correlation between the acid-induced loss of activity (i.e denaturation) of the enzyme and changes in the decay lifetimes of the labels were found suggesting the potential application of such fluorescent complexes as probes in real biological matrices without adverse effects on the natural characteristics of the system.