Photophysics of RuII complexes with 1,4,5,8-tetraazaphenanthrene, incorporated into sephadex SP C-25

Abstract

Photophysical properties of Ru^II-tris-(1,4,5,8-tetraazaphenanthrene)[Ru(tap)²⁺₃], Ru^II-tris-(2,2′-bipyridine)[Ru(bpy)²⁺₃], Ru(bpy)₂(tap)²⁺ and Ru(bpy)(tap)²⁺₂ have been compared when they are incorporated into Sephadex SP C-25, a cation–exchange resin, the swelling characteristics of which depend on the solvent in which it is suspended. Transient absorptions detected using diffuse reflectance laser flash photolysis for each ruthenium complex in Sephadex have been observed and shown to have identical decay kinetics to their emissions and have therefore been assigned to absorptions due to triplet metal–ligand charge-transfer excited states, ³MLCT. Emission decays from the complexes in Sephadex usually gave longer lifetimes when dry or swollen with organic solvents and shorter lifetimes when swollen with water. In dilute fluid solution the decay of emission from these ruthenium complexes was monoexponential but the emission observed when they were incorporated in dry or swollen Sephadex showed deviation from a monoexponential decay which increased with the number of tap ligands in the complex. Some of these decays were analysed using a dispersive kinetics model in which a distribution of activation energies associated with the decays was assumed. Possible mechanisms to explain these results were discussed.