Luminescence spectroscopy of Eu(Bis-tris)3+ complexes in anhydrous DMF [Bis-tris = 2,2-bis(hydroxymethyl)-2,2′,2″-nitrilotriethanol]: luminescence quenching rate constants for the 5D0 state of Eu3+ by DMF and polyalcoholic OH groups

Abstract

Excitation and emission spectra and luminescence lifetimes of Eu³⁺ complexes obtained by dissolving anhydrous EuCl₃ and EuCl₃/2,2-bis(hydroxymethyl)-2,2′,2″-nitrilotriethanol (Bis-tris) in anhydrous dimethylformamide (DMF) and those from a Eu(Bis-tris)₂Cl₃ crystalline sample have been studied. Two distinct Eu³⁺ complexes were observed when anhydrous EuCl₃ was dissolved in anhydrous DMF, and one was interpreted as an outer-sphere complex of Cl⁻ anion. Dissolution of an excess amount of vacuum dried NaClO₄ or KPF₆ in anhydrous DMF resulted in longer luminescence lifetimes, presumably reducing the effects of trace amounts of water in the solvent due to competitive binding of the water in the solvent by alkali metal cations. The quenching rate constant for the ⁵D₀ state of Eu³⁺ ion by each complexed DMF molecule in solution and by each OH group in the Bis-tris from the Eu(Bis-tris)₂Cl₃ crystalline sample were 54 ± 1 and 495 ± 5 s⁻¹, respectively, and these were used to interpret the plausible structures of the different Eu³⁺ complexes in the EuCl₃/Bis-tris/DMF solution.