Synthesis, Characterization and Fluorescence of N,N′‐Bis(6‐methyl‐2‐pyridinecarboxylamide‐N‐oxide)‐1,2‐ethane and Corresponding Rare Earth(III) Complexes

Abstract

A new ligand, N,N′‐bis(6‐methyl‐2‐pyridinecarboxylamide‐N‐oxide)‐1,2‐ethane (L), and its six lanthanide(III) complexes (RE=La, Sm, Eu, Tb, Gd, Yb) were synthesized and characterized in detail. The results indicate that the composition of the binary complexes was determined as [REL(H2O)2(NO3)2] NO3 · nH2O (n=0–2), that the six complexes are 1∶1 electrolytes in DMF, and that the Eu3+ complex has bright red fluorescence in a solid state. At the same time, we synthesized three complexes of Eu3+, Tb3+, and Gd3+ with 6‐methylpicolinic acid N‐oxide (L,). The intensity of sensitized luminescence for Eu3+ increases in the following order: L>L′. The energies of an excited triplet state for the ligands are 20704 cm−1 (L) and 20408 cm−1 (L′), respectively. The fact that the ligands strongly sensitized Eu3+ and the order of the emission intensity for the Eu3+ complexes were explained by the relative energy gap between the lowest triplet energy level of the ligands (T) and 5D of Eu3+ or Tb3+. This means that the triplet energy level of the ligand is the chief factor, which dominates RE3+ luminescence.