No abstract

We report a class of highly efficient electroluminescent materials based on fluorinated iridium compounds. Using aluminum as the cathode, a device, using fac-tris[5-fluoro-2(5-trifluoromethyl-2-pyridinyl)phenyl-C,N]iridium (Ir-2h) as the luminescent layer, displayed intense electroluminescence at 525 nm with an efficiency of 20 cd/A and a maximum radiance of 4800 cd/m2. Differing from the previously reported Ir(ppy)3, Ir-2h can be used in the undiluted form without the use of a charge-transporting host. This indicates that Ir-2h by itself has good enough charge-transporting properties. Photoluminescence studies at room temperature and 77 K revealed that electroluminescence originates from the metal-to-ligand charge transfer state with a quantum yield of 0.56 for Ir-2h and 0.5 for Ir(ppy)3 in toluene at room temperature. In the thin-film form, photoluminescence quantum yield of Ir-2h is a factor of 10 greater than that of Ir(ppy)3 due to the larger self-quenching effect of Ir(ppy)3.

A series of diiron(II) complexes, [Fe 2 (µ-L)(µ-O 2 CR)(O 2 CR)(N) 2 ], where L is a dinucleating bis-(carboxylate) ligand based on m-xylylenediamine bis(Kemp's triacid imide) and N is a pyridine-or imidazolederived ligand, were prepared as models for the carboxylate-bridged non-heme diiron cores of the O 2 -activating enzymes, soluble methane monooxygenase hydroxylase (MMOH), and the R2 subunit of ribonucleotide reductase (RNR-R2). X-ray crystallographic studies revealed differences in the coordination geometry of the bridging monocarboxylate ligand, which shifts from monodentate to syn,syn-bidentate bonding modes. The extent of this carboxylate shift depends on both the steric bulk of the monocarboxylate and the basicity of the ancillary N-donor ligands. Exposure of these diiron(II) complexes to O 2 at -77°C in nonpolar solvents (CH 2 Cl 2 , THF, toluene) yielded deep blue solutions (λ max ≈ 580 nm, ≈ 1200 M -1 cm -1 ), consistent with the generation of diiron(III) peroxo species. This reaction was irreversible, and its stoichiometry was determined by manometry to be 1:1 in diiron(II) complex and O 2 . The diiron(III) peroxo complexes exhibited oxygen isotope-sensitive resonance Raman bands at ∼860 cm -1 , which are assigned to the O-O stretching frequency of a µ-1,2-peroxodiiron(III) core. 57 Fe Mössbauer spectroscopy confirmed the assignment of the diiron(III) oxidation level and indicated that the two iron sites have inequivalent environments (δ 1 ≈ 0.47 mm s -1 , ∆E Q1 ≈ 0.88 mm s -1 ; δ 2 ≈ 0.63 mm s -1 , ∆E Q2 ≈ 1.20 mm s -1 ). Kinetics experiments provided rate constants for the reaction and revealed it to be first order in both diiron(II) complex and O 2 . The factors controlling the rate of formation of the blue species and its stability are discussed.