Syntheses, structures and luminescent properties of Sm (III) and Eu (III) chelates for organic electroluminescent device applications

Samarium(III) and europium(III) complexes of the β-diketone ligand (2-thienyl)trifluoroacetylacetone (HTTA) and triphenylphosphine oxide (TPPO) were prepared. The complexes, Sm(TTA)₂(TPPO)₂NO ₃ (1), Eu(TTA)₂(TPPO)₂NO₃H ₂O (2), and Eu(TTA)₃(TPPO)₂ (3) were characterized. Single crystal X-ray diffraction molecular structures of complexes 1 and 3 are presented and some of the crystal parameters for complex 1 are: space group, P1; a = 11.019(4) Å, b = 11.791(6) Å, c = 12.535(5) Å; α = 102.68(3)°, β = 102.06(3)°, γ = 117.75(3)°; for complex 3: space group, P - 1, a = 11.1946(9) Å, b = 12.117(2) Å, c = 23.535(2) Å, α = 80.047(13)°, β = 76.498(7)°, γ = 70.450(9)°. Electroluminescent devices were fabricated by vacuum evaporation. Apart from single layer devices, double and triple layer devices with the following structures: ITO/TPD/Complex 2/Al; ITO/TPD/Complex 3/Al; ITO/TPD/Complex 2/Alq/Al were studied, where N,N-bis(3-methylphenyl)-N,N′-diphenyl-benzidine (TPD) was used as a hole transporting layer and tris(8-hydroxyquinolinate)aluminum (Alq) as an electron transporting layer. The results indicate that single layer devices show very low quantum efficiency, while the double layer devices with a hole transporting layer exhibit enhanced efficiency and a well defined EL spectrum. No significant improvement was observed in the triple layer devices with an additional electron transporting layer.