Modified dipicolinic acid ligands for sensitization of europium(III) luminescence.
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.
School of Chemistry, University of Southampton, Highfield, UK.
Michael R
MR
George
Christopher A
CA
Golden
Martin C
MC
Grossel
Richard J
RJ
Curry