Modified pyridine-2,6-dicarboxylate acid ligands for sensitization of near-infrared luminescence from lanthanide ions (Ln3+ = Pr3+, Nd3+, Gd3+, Dy3+, Er3+)

A detailed study of the ability of pyridine-2,6-dicarboxylic acid (1) and its 4 -mono- and 3,4,5-tri-substituted analogues to sensitize emission from Pr3+, Nd3+, Gd3+, Dy3+ and Er3+ is presented. Sensitization of Ln(3+) emission was demonstrated via the ligands in all complexes, excluding Gd3+, with emission covering the spectral range from 500 nm to 1850 nm obtained with variation of the Ln(3+) ion. From the study of the ligand-based photoluminescence obtained from Gd3+-complexes, and the relative ligand and Ln(3+) emission obtained from the other complexes, the singlet and triplet state energies of complexes of (1) are estimated to be at 3.1 eV and 2.6 eV respectively whilst for the 3,5-dibromo-substituted complexes (4) they are at 2.9 eV and 2.3 eV. Hypersensitivity of the Er3+ I-4(15/2) -> H-2(11/2) and I-4(15/2) -> (4)G(11/2) intra-atomic transitions is also observed in the 4-chloro-substituted (3) complex. Enhanced sensitization of Nd3+ (ca. 5-fold) and Er3+ (ca. 2-fold) near-infrared emission is demonstrated for complexes of (3) and (4) respectively in comparison with those of (1).

Automated summary

A study was conducted on the ability of pyridine-2,6-dicarboxylic acid and its analogues to sensitize emission from various rare earth ions, showing different sensitization effects. The 4-chloro-substituted complex demonstrated enhanced near-infrared emission for Nd3+ and Er3+, indicating potential applications in this area.