pH Dependence of Absorption and Emission Spectra of Ru(phen)2(phenOH)2+(PF6)2 Complex

A ruthenium complex of the 4-hydroxy- 1,10-phenanthroline ligand was synthesized, and the variation of its absorption and emission intensity and litetime with pH characterized. Excited state lifetime, luminescence intensity, and emission properties were determined.  The complex exhibits a maximum at 460nm, and a small red shift at higher pH. The spectra show a well defined isobestic point. Luminescence intensity exhibited a sigmoidal relationship with pH, a behaviour that is similar to those of other ruthenium complexes carrying protonable functional groups. This characteristic is suggestive of the suitability of this complex for pH sensor design for medical practices as well as industrial processes. pH dependence is more evident in the emission than the absorption spectra, a behaviour characteristic of higher pH dependence on the excited than the ground state of the complex. Emission lifetimes of 165.4ns and 3.08ns for the protonated and deprotonated states respectively, were determined and the pK * a value calculated as 3.68.