Synthesis, structures, photo- and electro-luminescent properties of novel oxadiazole-functionlized europium(iii) benzamide complexes

Abstract

With N-(5-phenyl-1,3,4-oxadiazol-2-yl)-benzamide (HL₁) as the first ligand, three new luminescent europium complexes Eu₂Na₂(L₁)₆(OH)₂·2C₂H₅OH·2CHCl₃ (1), Eu(L₁)₃(phen) (phen = 1,10-phenanthroline) (2) and Eu₂Na₂(L₁)₆(L₂)₂(OH)₂·8CHCl₃ [L₂ = 2,5-bis(2-pyridyl)-1,3,4-oxadiazole] (3) have been prepared and structurally characterized. Each ligand L₁ coordinates with a Eu³⁺ ion through a carbonyl oxygen atom and oxadiazol nitrogen atom, the coordination geometry at europium is a distorted square antiprism. Complexes 1 and 3 have centrosymmetric dimeric structural features with OH⁻ as the bridging ligand, while 2 is mononuclear with phen as the neutral ligand. All these complexes show efficient red emissions typical of Eu³⁺ ions at room temperature, the overall quantum yields of complexes 1, 2 and 3 were 0.15, 0.37 and 0.23, respectively. Using Eu(L₁)₃(phen) as the emitting material, an electroluminescent device with the structure ITO/TPD (30 nm)/Eu(L₁)₃(phen): TPD (1 : 3, 50 nm)/AlQ (30 nm)/Mg_0.9Ag_0.1/Ag was fabricated. The device emits sharp red light originating from europium complex, demonstrating that Eu(L₁)₃(phen) is a promising red emitter with good electron-transporting property.