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

Samarium(111) and europium(111) complexes of the beta-diketone ligand (2-thienyl)trifluoroacetyl acetone (HTTA) and triphenylphosphine oxide (TPPO) were prepared. The complexes, Sm(TTA)(2)(TPPO)(2)NO3 (1), Eu(TTA)(2)(TPPO)(2)NO3H2O (2), and Eu(TTA)(3)(TPPO)(2) (3) were characterized. Single crystal X-ray diffraction molecular structures of complexes I and 3 are presented and some of the crystal parameters for complex I are: space group, P1 a = 11.019(4) Angstrom, b = 11.791(6) Angstrom, c = 12.535(5) Angstrom; alpha = 102.68(3)degrees, beta = 102.06(3)degrees, gamma = 117.75(3)degrees; for complex 3: space group, P - 1, a = 11.1946(9) Angstrom, b = 12.117(2) Angstrom, c = 23.535(2) Angstrom, alpha = 80.047(13)degrees, beta = 76.498(7)degrees, gamma = 70.450(9)degrees. 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. (C) 2003 Elsevier B.V. All rights reserved.