Intense Near-Infrared Luminescence of a Mesomorphic Ionic Liquid Doped with Lanthanide β-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)