Mechanism of intermolecular energy transfer between tris(acetylacetonato)lanthanoid complexes in solution
Abstract
Intermolecular energy transfer between excited state Tb3+ ions in Tb(aa)33H2O and Ln3+ions in Ln(aa)33H2O, where aa = acetylacetonate, Ln = Eu and Sm is shown to be markedly solvent dependent. It is proposed that the Tb3+→ Ln3+ energy transfer occurs in mixed metal dimers where the Tb–Ln distance is likely to be ∼0.4 nm. The solvent dependent behaviour is related to the relative concentrations of monomeric and dimeric species in the various solvents. The rate controlling step in the intermolecular energy transfer is probably that of monomer–dimer reaction which at 273 K is of the order of 105 dm3 mol–1 s–1. The activation energy of this reaction between Tb, Eu and Sm acetylacetonates is estimated to be ∼ 23 kJ mol–1.