Ru(phen)2(PHEHAT)]2+ and [Ru(phen)2(HATPHE)]2+: two ruthenium(II) complexes with the same ligands but different photophysics and spectroelectrochemistry

The properties of two mononuclear Ru(II) complexes formed with the extended planar ligand PHEHAT depend drastically on the chelation site by the metallic ion. When the chelation takes place on the HAT site of the ligand (case of the novel complex Ru(phen)2(HATPHE)]2+), the emission behavior is quite similar to that of Ru(phen)2(HAT)]2+. In contrast, when the chelation is on the phen motif of the ligand (case of Ru(phen)2(PHEHAT)]2+), the spectroscopic (absorption and emission) and electrochemical data for the complex do not obey the linear spectroelectrochemical correlation and the emission behavior is comparable to that of the extensively studied dppz complex (Ru(phen/bpy)2(dppz)]2+). Thus, for Ru(phen)2(PHEHAT)]2+, the emission lifetimes and intensities as a function of temperature exhibit a maximum for nitrile solvents. However, in contrast to the dppz case, at least three different states (two emitting and one dark) participate in the deactivation with different contributions depending on the temperature. These different contributions explain the observed maximum. Moreover, the fact that the solvent is liquid or frozen also influences the nature of the luminescent species.