Intermolecular energy transfer between tris(acetylacetonato)-lanthanoid complexes in n-butanol solution

Abstract

Intermolecular energy transfer occurs between Tb(aa)₃3H₂O and Ln(aa)₃3H₂O complexes (Ln = Pr, Nd, Sm, Eu, Dy, Ho or Er; aa = acetylacetonate) in n-butanol solution at 293 K. Measurement of the decay time of the Tb^{3 + 5}D₄ level indicates that transfer occurs from this level to excited levels of the Ln³⁺ ions with bimolecular rate constants within the range 0.5–4.9 × 10⁵ dm³ mol s^–1. Data from similar measurements on a mixed crystal Eu_xTb_(1–x)(aa)₃3H₂O and other considerations indicate that this is a very short range electron-exchange transfer. Similar measurements of the Tb³⁺ ion phosphorescence yield indicate the presence of a further intermolecular transfer process between a higher excited state of the Tb³⁺ complex and the added Ln³⁺ complexes. The Stern–Volmer quenching constants vary from 11 dm³ mol^–1 for Ho and Sm to 110 dm³ mol^–1 for Pr. It is concluded that this transfer is unlikely to occur from either the ligand singlet or triplet levels and it is proposed that a higher Tb³⁺ level such as the ⁵D₃ may be involved in both inter- and intramolecular energy transfer.