Modified Dipicolinic Acid Ligands for Sensitization of Europium(III) Luminescence

Abstract

The effect of substitution at the 4 and 3,5 positions in the pyridine ring of europium(III) pyridine-2,6-dicarboxylate complexes has been investigated with particular emphasis on sensitization of the Eu3+ ion. Sensitization of the Eu3+ 615-nm emission was achieved through excitation of the ligands in which the 4 substituent was -H, -OH, and -Cl and the 3,5 position was -H. In these cases, the ligand-to-Eu3+ ratio was confirmed as being 3:1. The sensitization was found to increase following substitution of the 4 position in the order Cl > H > OH. This is attributed to energy transfer occurring from the ligands into different Eu3+ intra-atomic energy levels, with spin selection rules governing the efficiency of this process. The Eu3+ luminescence lifetime was measured and found to vary from 1.16 to 2.90 ms depending on the excitation energy, ligand, and solvent. For the case of the 3,5-dibromo-4-hydroxy derivative, no sensitization was observed and a ligand-to-Eu3+ ratio of 1:1 was found. The solubility of these complexes in water and their long emission lifetime make them attractive for use as probes in biological systems.

Europium Complexes of Tris(dipicolinato) Derivatives Coupled to Methylumbelliferone: A Double Sensitization

“…Apart from the parent dipic compound, the pyridine ring can be functionalized, in particular at its para position, the influence of the grafted substituent being well documented by several authors. [14][15][16][17][18][19] These couplings have often resulted in a decrease in luminescence efficiency relative to dipicolinic acid, due to a mismatch of the triplet states of the complexed ligands with the excited states of the lanthanides. However, promising results have also been achieved with substantial increase in [ either mostly on the dipicolinate (DPA) backbone (at 280 nm) or exclusively on the coupled coumarin chromophore in the near visible range (320 nm).…”

The potential of pyridine-2,6-dicarboxylic acid based organolanthanide complexes for efficient near-infrared emission

“…In particular the absorption corresponding to the 4 F 3/2 energy level can be seen to consist of a clear doublet peak with an splitting energy of ~120 cm -1 for each complex. The crystal structure of the molecules has also been confirmed for analogous Eu 3+ complexes using X-Ray crystallography and complementary spectroscopic measurements 24 . Figure 3 shows the photoluminescence spectrum of Nd 3+ (DPA) 3 excited using the 457.9 nm laser line obtained from a solid-state sample.…”

Luminescence of Eu3+ ions in hybrid polymer‐inorganic composites based on poly(methyl methacrylate) and zirconia nanoparticles

“…For this reason, direct exciting of Ln 3+ becomes successful in rare instances. The latter is due to the parity exclusion principle, as a result of which the lanthanide ions have low overlap vibrational and electronic states and 4f wave functions . The problem is solved by introducing lanthanide ions into organic or crystalline matrices.…”