Synthesis, structure and OLED application of a new europium(III) complex: {tris-(thenoyltrifluoroacetonate)[1,2,5]selenadiazolo[3,4-f][1,10]phenanthroline}europium(III)

Herein we describe the synthesis, characterization and spectroscopic properties of the complex tris-(thenoyltrifluoroacetonate)([1,2,5]selenadiazolo[3,4-f][1,10]phenanthroline) europium(III) acetonitrile solvate, [Eu(TTA)3PhenSe]1.5CH3CN, where TTA = 2-thenoyl trifluoroacetone and PhenSe = [1,2,5]selenadiazolo[3,4-f][1,10]phenanthroline. X-ray crystallography reveals that it is an eight-coordinate Eu(III) complex, containing three β-diketonate chelates and one N,N-bidentate ligand, [1,2,5]selenadiazolo[3,4-f][1,10]phenanthroline. Under excitation at 350 nm at room temperature, the europium complex in chloroform solution displayed the typical Eu(III) red emission as a sharp band at 612 nm, characteristic of Eu(III) electronic transition 5D0-7F2. Thermally evaporated films of this complex showed the same emission band under photoexcitation. However, the electroluminescence from multilayer devices displayed different profiles. The 5D0 → 7FJ (J = 0, 1, 2, 3 and 4) transitions of Eu(III) ion appear over a broad emission band which can be attributed to the electroluminescence of the ligand or excimer formation. Although light emitting diodes show the same profile independently of driving voltage, the intensity ratio of the peaks is determined by the active layer thickness, allowing us to obtain light sources varying from orange to red.