Influence of counter ions on structure, morphology, thermal stability of lanthanide complexes containing dipicolinic acid ligand.

Two kinds of lanthanide coordination polymers formed by dipicolinic acid with lanthanide ions were synthesized by varying the counter ions. And their crystal structures, morphology and thermal stabilities were measured and compared. X-ray single-crystal diffraction analysis reveals that Na3[Ln(DPA)3] (Ln = Tb or Eu) stretches to a rigid network by means of bridging Na+ ion. Moreover, Na3[Ln(DPA)]3 exhibits good thermal stability and luminescent properties, and its optical properties can be remained even after heating at 200 °C more than 3 days. However, when Na+ in Na3[Ln(DPA)3] was replaced with NH4+, i.e., (NH4)3[Ln(DPA)3] with a supramolecular structure based on π-π stacking and other weak interactions, shows relatively poor thermal stability which leads to deterioration of their luminescence properties after heating treatment. This result confirms that the rigid frame structure of Na3[Ln(DPA)]3 plays a crucial role in improving its thermal stability and keeping its highly luminescent quantum efficiency.

Water-soluble Tb(3+) and Eu(3+) complexes based on task-specific ionic liquid ligands and their application in luminescent poly(vinyl alcohol) films.

Novel water-soluble lanthanide complexes (Ln(IMI-DPA)3) have been synthesized using the task-specific ionic liquid consisting of a dipicolinic acid motif as the sensitizer of lanthanide luminescence. In Ln(IMI-DPA)3, Ln(3+) ions are in 9-fold coordination through six carboxylate oxygen atoms and three nitrogen atoms in pyridine units, and the water molecule is excluded from the coordination sphere of the lanthanides. It is found that Ln(IMI-DPA)3 possess bright luminescence, long luminescence lifetime in aqueous solution, high thermal stability and good water solubility. Furthermore, these complexes can be incorporated into water-soluble poly(vinyl alcohol) (PVA) matrixes to obtain highly luminescent, transparent and flexible PVA composite films. The emission colors of the films can be tuned from red, orange, yellow, light green, green to white light by regulating the concentration of the various luminescent components.