Isotope and temperature dependence of dual emission in a mononuclear ruthenium(II) polypyridyl compound

Detailed photophysical measurements on a series of [Ru(bpy)(2)(L)](n+) comp lexes, which are deuterated to varying degrees are reported, where bpy is 2 ,2'-bipyridyl and L is 3-(pyrazin-2-yl)-1,2,4-triazole (Hpztr) or 3-(pyridi n-2-yl)-1,2,4-triazole (Hpytr). For the pyridinyltriazole complexes, deuter ation of bpy leads to a doubling of the emission lifetime, while deuteratio n of the triazole ligand has no effect on the emission lifetime. For the co mplex containing the protonated pyrazinyltriazole ligand, deuteration of bp y does not affect the emission lifetime, but the lifetime is strongly affec ted by the deuteration of the triazole-containing ligand. These observation s indicate that in the pyridinyltriazole complexes the emitting state is bp y based, while for the complex containing the protonated pyrazinyltriazole ligand the emission is pyrazine based. For the compound containing the depr otonated pyrazinyltriazole ligand a remarkable insensitivity of the emissio n lifetime to deuteration is observed. Time-resolved resonance Raman data c learly indicate that the emitting triplet state is bpy based at room temper ature when the triazole is deprotonated and switches to being pyrazine base d on protonation. Variable temperature emission studies on the deprotonated complex reveal a remarkable dual emission between 120 and 200 K. The two e mitting states exhibit different lifetime dependences on temperature. It is proposed that the presence of these two, weakly coupled emitting states, o ne bpy and one pyrazine based, is responsible for the relative insensitivit y of the emission lifetime of the deprotonated pyrazinyltriazole complex to deuteration.