Inorganic photophysics in solution. Part 1.—Temperature activation of decay processes in the luminescence of tris(2,2′-bipyridine)ruthenium(II) and tris(1,10-phenanthroline)ruthenium(II) ions

Abstract

The luminescence lifetimes of [Ru(bipy)₃]²⁺ and [Ru(phen)₃]²⁺ have been determined in a variety of media, over as wide a temperature range as feasible in each case (with a lower limit of 77 K). These results, together with a reinterpreting of certain others in the literature, indicate that the deactivation of the luminescent state of both complexes proceeds through two energy-controlled pathways. For [Ru(bipy)₃]²⁺ one of these is characterised by a relatively large activation energy (≈ 48 kJ mol^{– 1}) which dominates at T 270 K, whilst the other route, which dominates at T < 130 K has an activation energy ≈ 2 kJ mol^{– 1} in fluid media, but only 0.64 kJ mol^{– 1} in a polymer film. In 9 mol dm^{– 3} LiCl + water (H₂O and D₂O) media, the low-energy term is 1.77 kJ mol^{– 1} above the glass transition region, but 0.65 kJ mol^{– 1} below T_g, indicating the importance of solvation forces. An exactly analogous pattern of results is shown by [Ru(phen)₃]²⁺. A simple energy-level model is proposed which covers the luminescence behaviour from cryogenic to ambient temperatures.