Synthesis, characterization and properties of 1,2,4-triazolo[3,4-b][1,3,4]thiadiazole derivatives and their europium complexes

Eight novel 1,2,4-triazolo[3,4-b][1,3,4]thiadiazole derivatives and their corresponding Eu(III) complexes were synthesized and characterized. From the spectral studies it has been concluded that the title Eu(III) complexes display six coordination. The investigation of the luminescence properties of the title complexes showed that the ligands favor energy transfers to the emitting energy level of europium ions. The title Eu(III) complexes exhibited characteristic emissions of europium ions, and possessed strong luminescence intensities, good fluorescence quantum yields, and the highest fluorescence quantum yield is up to 0.522. Furthermore, the luminescence intensity of the complex with chlorine-substituted group is the strongest than that of other complexes. The exploration of the electrochemical properties of the title complexes shows that the introduction of electron-donating groups can increase the HOMO energy levels, LUMO energy levels and the oxidation potential of the complexes, however, the result of introduction of electron-withdrawing groups was just opposite.