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.