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[gt-or-equal] 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 Tg, 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.