Synthesis, characterization and fluorescence of N,N'-BIS (6-metyl-2-pyridine-carboxylamide-N-oxide)-1,2-ethane and corresponding rare earth (III) complexes

Abstract

A new ligand, N,N-BIS (6-metyl-2-pyridinecarboxylamide-N-oxide)-1,2-ethane (L) and six lanthanide(III) complexes (RE=La, Sm, Eu, Tb, Gd, Yb) were synthesized and characterized in detail. The results indicated that the composition of the binary complexes was determined as [REL(H 2O)(NO 3) 2]NO 3· nH 2O ( n=0–2), and the Eu 3+ complex had bright red fluorescence in solid state. Three complexes of Eu 3+, Tb 3+, and Gd 3+ with 6-methylpicolinic acid N-oxide (L') were also synthesized. The relative intensity of sensitized luminescence for Eu 3+ increased in the following order: L>L'. The phosphorescence spectra of the Gd 3+ complexes at 77 K were measured. The energies of excited triplet state for the ligands were 20704 cm −1 (L) and 20408 cm −1 (L'). The facts that the ligands sensitized Eu 3+ strongly and the order of the emission intensity for Eu 3+ complexes were explained by Δ E(T- 5D). This meant that the triplet energy level of the ligand was the main factor to influence RE 3+ luminescence.