Luminescent lanthanide complexes based on pyridine-2,6-dicarboxamide and 1,2,4-triazole-3-carboxylic acid ligands as F− anion sensor

Abstract

Different luminescent europium complexes were synthesized by the reaction of pyridine-2,6-dicarboxamide (pdcam), 1,2,4-triazole-3-carboxylic (trzc) and EuCl3 solutions in different molar ratios. The synthesized europium complexes [Eu(pdcam)2(trzc)]Cl3 (1), [Eu(pdcam)(trzc)2]Cl3 (2) and [Eu(pdcam)1.5(trzc)1.5]Cl3 (3) were characterized by elemental analysis, FT-IR spectroscopy, powder XRD studies, SEM, TGA, UV–vis and photoluminescence spectroscopy. Thermal stability results indicated that the complexes were relatively stable at high temperature. Among all the complexes, the highest lifetime and intrinsic quantum efficiency were observed for complex [Eu(pdcam)2(trzc)]Cl3 (ɸEu=48.83% and τ=1.31ms). The anion sensing properties of europium complexes had been studied in detail using absorption and emission spectral studies. The complexes showed significant changes in luminescence upon hydrogen binding to F− ions. It was noted that luminescence of the complexes was completely quenched by 4 equivalents of F− ions in DMSO solution hence these complexes can be utilized as fluorescent probes for F− ions. Maximum fluorescence quenching degree (9.8) was observed for complex (1).