Inorganic photophysics in solution. Part 4.—Deactivation mechanisms of the 2Eg state of CrIII complexes from lifetime studies

Abstract

The temperature dependences of the luminescence lifetimes, τ_lum, of several Cr^III complexes of particular photochemical interest have been determined over temperature ranges 77–370 K in a variety of media, especially 9 mol dm^–3 LiCl + H₂O and cellulose acetate film. In most cases, k_lum fits an expression k_Tl+A_NR exp(–ΔE^{[graphic omitted]}_NR/RT) where the subscripts refer to temperature-independent and (temperature-dependent) non-radiative terms. The strong solvent-dependence of ΔE^{[graphic omitted]}_NR, which is always only a fraction of the ⁴T_2g–²E_g splitting, suggests a chemical pathway for deactivation of the ²E_g state rather than a purely physical route such as back-intersystem crossing. For complexes which have been examined in a wide variety of media, values of ln A_NR correlate fairly well with those of ΔE^{[graphic omitted]}_NR, implying a common overall mechanism.