Synthesis and luminescence properties of novel 8-hydroxyquinoline derivatives and their Eu(III) complexes

Six novel 8-hydroxyquinoline derivatives were synthesized using 2-methyl-8-hydroxyquinoline and para-substituted phenol as the main starting materials, and were characterized by ¹ H nuclear magnetic resonance (NMR), mass spectrometry (MS), ultraviolet (UV) light analysis and infra-red (IR) light analysis. Their complexes with Eu(III) were also prepared and characterized by elemental analysis, molar conductivity, UV light analysis, IR light analysis, and thermogravimetric-differential thermal analysis (TG-DTA). The results showed that the ligand coordinated well with Eu(III) ions and had excellent thermal stability. The structure of the target complex was EuY^1-6 (NO₃ )₃ .2H₂ O. The luminescence properties of the target complexes were investigated, the results indicated that all target complexes had favorable luminescence properties and that the introduction of an electron-donating group could enhance the luminescence intensity of the corresponding complexes, but the addition of an electron-withdrawing group had the opposite effect. Among all the target complexes, the methoxy-substituted complex (-OCH₃ ) had the highest fluorescence intensity and the nitro-substituted complex (-NO₂ ) had the weakest fluorescence intensity. The results showed that 8-hydroxyquinoline derivatives had good energy transfer efficiency for the Eu(III) ion. All the target complexes had a relatively high fluorescence quantum yield. The fluorescence quantum yield of the complex EuY³ (NO₃ )₃ .2H₂ O was highest among all target complexes and was up to 0.628. Because of excellent luminescence properties and thermal stabilities of the Eu(III) complexes, they could be used as promising candidate luminescent materials.