Acid–Base Behaviour in the Absorption and Emission Spectra of Ruthenium(II) Complexes with Hydroxy-Substituted Bipyridine and Phenanthroline Ligands

Two bis(2,2′-bipyridyl)ruthenium(II) complexes bearing hydroxy-substituted diimine ligands [Ru^II(bpy)₂(N-N)](BF₄)₂(N-N = phenOH or bpyOH) have been synthesized and characterized. These complexes can be readily deprotonated under basic conditions to yield the deprotonated forms [Ru^II(bpy)₂(N-N)](BF₄) (N-N = phenO^–or bpyO^–). The structures of one of the complexes and its deprotonated form have been determined by X-ray crystallography. The photophysical and electrochemical properties of these complexes have been examined. Detailed photophysical studies showed that the luminescent properties of these complexes are sensitive to the nature of the solvent media. In addition, the emission properties of these complexes exhibit a strong dependence on the pH of the aqueous medium, and hence these complexes are potentially useful as phosphorescent pH probes.