Intense near-infrared luminescence of a mesomorphic ionic liquid doped with lanthanide b-diketonate ternary complexes

The ionic liquid 1-dodecyl-3-methylimidazole chloride ([C12- mim]Cl) is doped with 1 mol-% of the lanthanide ternary complexes [Ln(tta)3(phen)] (tta = thenoyltrifluoroacetonate, phen = 1,10-phenanthroline, Ln = Nd, Eu, Er, Yb), resulting in luminescent mesogenic phases at room temperature. According to DSC and SAXS measurements, the temperature of the crystal liquid crystal transition is below 10 °C. Analysis of vibrational and luminescence data points to the inner co-ordination sphere of the EuIII ion being very similar in both the mesomorphic sample and the parent β-diketonate complex. The mesomorphic samples containing NdIII, ErIII, or YbIII display relatively intense near-infrared luminescence. This emission is enhanced in the liquid crystalline phases with respect to the initial compounds, as demonstrated for instance by the quantum yield of the [Yb(tta)3(phen)]-containing mesogenic sample which amounts to 2.1%, as compared to 1.6 and 1.1%for the powdered ternary complex and its solution in toluene, respectively. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)