Synthesis, characterizations and luminescent properties of three novel aryl amide type ligands and their lanthanide complexes

Three new aryl amide type ligands, N-(phenyl)-2-(quinolin-8-yloxy)acetamide (L1), N-(benzyl)-2-(quinolin-8-yloxy)acetamide (L2) and N-(naphthalene-1-yl)-2-(quinolin-8-yloxy)acetamide (L3) were synthesized. With these ligands, three series of lanthanide(III) complexes were prepared: [Ln(L1)2(NO3)2]NO3, [Ln(L2)2(NO3)2(H2O)2]NO3·H2O and [Ln(L3)2(NO3)2(H2O)2]NO3·H2O (Ln = La, Sm, Eu, Gd). The complexes were characterized by the elemental analyses, molar conductivity, 1H NMR spectra, IR spectra and TG-DTA. The fluorescence properties of complexes in the solid state and the triplet state energies of the ligands were studied in detail, respectively. It was found that the Eu(III) complexes have bright red fluorescence in solid state. The energies of excited triplet state for the three ligands are 20 325 cm−1 (L3), 21 053 cm−1 (L2) and 22 831 cm−1 (L1), respectively. All the three ligands sensitize Eu(III) strongly and the order of the emission intensity for the Eu(III) complexes with the three ligands is L3 > L2 > L1. It can be explained by the relative energy gap between the lowest triplet energy level of the ligand (T) and 5D1 of Eu(III). This means that the triplet energy level of the ligand is the chief factor, which dominates Eu(III) complexes luminescence.