EuIII luminescence in a hygroscopic ionic liquid:: Effect of water and evidence for a complexation process

The spectroscopic characteristics (excitation, emission and lifetime) of Eu-III dissolved in 1-methyl-3-butyhmidazolium bis(trifluoromethanesulfon)imide (BumimTf(2)N) are reported. In a first series of experiments, the effect of the presence of water in BumimTf(2)N was examined. It appears that non-degassed solutions are most probably inhomogeneous, displaying large water clusters leading to an intense diffusion of the red light of an He:Ne laser. In these samples, the Eu emission spectrum is close to that observed in slightly acidic aqueous solutions. In contrast, when the samples were de-gassed the solution appeared homogeneous and water can be considered as a competitive ligand for the first coordination sphere of Eu. In a subsequent series of experiments, tetrabutylammonium chloride (TBACl) was added to the solution and the resultant species investigated. The ensuing enhancement in the metal-centered luminescence has been interpreted in terms of changes in the inner coordination sphere of the Eu-III ion and possible structures are discussed. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.