Comparison of Ground and Excited States of [Ru(bpy)2(η2-tpy)]2+ (bpy = 2,2'-Bipyridine; tpy = Terpyridine) and Associated Protonation Chemistry

Here, the ground and excited state dynamics of [Ru(bpy)2(η2-tpy)]2+ were studied. Protonation of the pendant pyridine ring of [Ru(bpy)2(η2-tpy)]2+ demonstrates that intra-ligand charge transfer (ILCT) occurs between the pendant pyridine and adjacent bpy ligand in the [Ru(bpy)2(η2-tpy)]2+ complex. The addition of trifluroacetic acid (TFA) results in slight spectral changes which have been assigned to the protonation of the pendant pyridine of [Ru(bpy)2(η2-tpy)]2+. The protonation of the pendant pyridine increases the lifetime from 0.082 ns to 2.6 ns. Mulliken-Hush analysis of the ILCT of [Ru(bpy)2(η2-tpy)]2+ has been done and compared with that of [Ru(bpy)3]2+. The value for the electronic coupling element (HDA) for [Ru(bpy)2(η2-tpyH+)]3+ suggests that the electronic coupling between bpy and the pendant pyridine is quite strong.