Photophysics of ruthenium(II) complexes with 2-(2′-pyridyl) pyrimidine and 2,2′-bipyridine ligands in fluid solution

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The photophysics of three complexes of the form Ru(bpy) 3− ϱ (pypm) ϱ 2+ (where bpy2,2′-bipyridine, pypm 2-(2′-pyridyl)pyrimidine and p=1, 2 or 3) was examined in H 2O, propylene carbonate, CH 3CN and 4:1 (v/v) C 2H 5OHCH 3OH; comparison was made with the well-known photophysical behavior of Ru(bpy) 3 2+. The lifetimes of the luminescent metal-to-ligand charge transfer (MLCT) excited states were determined as a function of temperature (between −103 and 90 °C, depending on the solvent), from which were extracted the rate constants for radiative and non-radiative decay and ΔE, the energy gap between the MLCT and metal-centered (MC) excited states. The results indicate that ∗Ru(bpy) 2(pypm) 2+ decays via a higher lying MLCT state, whereas ∗Ru(pypm) 3 2+ and ∗Ru(pypm) 2(bpy) 2+ decay predominantly via the MC state.