Photoinduced ligand isomerisation in a pyrazine containing ruthenium polypyridyl complex

Photochemically induced ligand rearrangements for the N2 and N4 coordination isomers of the complex [Ru(bpy)2(Hpztr)]2+ and its deprotonated analogue [Ru(bpy)2(pztr)]+, where bpy is 2,2’-bipyridyl and Hpztr is pyrazine-1,2,4-triazole ligand, are reported. 1H NMR spectroscopic and HPLC studies indicate that in acetone and acetonitrile the complexes are photostable when the triazole ring is deprotonated. Irradiation of the protonated N2 isomer in acetone results in formation of the N4 isomer, with the N4 isomer being photostable. In acetonitrile both isomers show photolability of the triazole based ligand and full dissociation to form [Ru(bpy)2(CH3CN)2]2+ is observed. The activation parameters for the population of the 3MC state from the lowest 3MLCT manifold, as obtained from temperature dependent emission lifetime studies, are reported and their relevance to the observed photochemical behaviour is considered. The results obtained are discussed in relation the analogous pyridine-triazole complexes.