[Show abstract][Hide abstract] ABSTRACT: We present the strategic design and synthesis of Os(II) complexes bearing a single pyridyl azolate pi-chromophore with an aim to attain high efficiency blue phosphorescence by way of localized transition. It turns out that our proposal of localized excitation seems to work well upon anchoring a single pi-chromophore on the Os(II) complexes such that the control of MLCT versus pipi* (or even LLCT) transitions is more straightforward. Among the titled complexes, [Os(CO)3(tfa)(fppz)] (1) and [Os(CO)3(tfa)(fbtz)] (5) (tfa=trifluoroacetate, (fppz)H=3-(trifluoromethyl)-5-(2-pyridyl)pyrazole, and (fbtz)H=3-(trifluoromethyl)-5-(4-tert-butyl-2-pyridyl)-1,2,4-triazole) give the anticipated blue phosphorescence with efficiencies of 0.26 (lambdamax=460 nm) and 0.27 (lambdamax=450 nm), respectively. For their halide analogues [Os(CO)3(X)(fppz)] (2, X=Cl; 3, X=Br; 4, X=I) and phosphine-substituted isomeric derivatives [Os(tfa)(fppz)(PPh2Me)2(CO)] (6-8), the localization of the excitation energy seems to populate at certain vibrational modes with weak bonding strength and hence an associated shallow potential energy surface to induce a facile radiationless transition. Furthermore, their ancillary ligands play an important role in fine-tuning not only the energy gap but also the emission intensity, i.e., in manifesting the radiationless transition pathways. Our results clearly show that there is always a tradeoff upon varying the parameters in an aim to optimize the hue and efficiency of phosphorescence toward blue.
[Show abstract][Hide abstract] ABSTRACT: Preparation of a new series of neutral metal complexes [(cod)Ir(fppz)] (1), [(cod)Ir(bppz)] (2), [(cod)Ir(fptz)] (3) and [(cod)Ir(bptz)] (4), bearing one cod ligand and a pyridyl azolate chelate are reported. A single-crystal X-ray diffraction study of 3 reveals the expected distorted square-planar geometry. The lowest absorption band consists of IrI atom increased triplet dpi-->pi* transitions (3MLCT), the assignment of which is firmly supported by the theoretical approaches. Complexes 1-4 exhibit weak phosphorescence in degassed solution at room temperature, whereas much more intense, solid-state phosphorescence appears in the range 622-649 nm. The pure MLCT emission was used as a prototypical model to address its remarkable spectral differences from the IrIII isoquinoline pyrrolide complex (5), which has mainly 3pipi phosphorescence. Complex 3 was used as a dopant to fabricate red-emitting phosphorescent organic light-emitting diodes (OLEDs). For the 7 % doped device, a maximum brightness of 3010 cd m-2 was achieved at an applied voltage of 15 V and with CIE coordinates of (0.56, 0.33), demonstrating for the first time the potential of neutral IrI complexes in OLED applications.
Chemistry - A European Journal 12/2006; 13(9):2686 - 2694. DOI:10.1002/chem.200601019 · 5.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Luminescent complexes: Through the design and synthesis of a series of new osmium-based β-diketonate carbonyl complexes (see picture; MLCT=metal-to-ligand charge transfer, kisc=intersystem crossing constant), a remarkable aromatic tunable fluorescence/phosphorescence ratio was explored. The relative luminescent efficiencies and associated dynamics were evaluated.
[Show abstract][Hide abstract] ABSTRACT: A new series of Os(II) diimine complexes with the general formula [Os(N(wedge)N)(CO)(2)I(2)], N(wedge)N = 2,2'-bipyridine (bpy) (1), 4,4'-di-tert-butyl-2,2'-bipyridine (dbubpy) (2), 4,7-diphenyl-1,10-phenanthroline (dpphen) (3), 2-(2'-pyridyl)benzoxazole (pboz) (4), and 5-tert-butyl-2-(2'-pyridyl)benzoxazole (bupboz) (5), were synthesized and characterized by spectroscopic methods and by a single-crystal X-ray diffraction study on the dpphen complex 3. The corresponding photophysical properties were studied using UV-vis and emission spectrometry. The resulting phosphorescence features both in solution and as a solid film, in combination with the MO calculation, lead us to conclude that the emissions originate from mixed halide-to-ligand (XLCT approximately 70%) and metal-to-ligand (MLCT approximately 30%) transitions instead of the typical MLCT transition. Using complexes 4 and 5 as the dopant emitters, we evaluated their potential to serve as a phosphor for organic light emitting diodes by examining their electroluminescent performances. Reddish orange electroluminescence centered around 600 nm was observed for organic light emitting diodes (OLEDs) fabricated using complex 5 as the emitter; the device efficiency was shown to be as high as 2.8% (and 5.0 cd/A or 2.7 lm/W), and the peak luminance was shown to be 5600 cd/m(2) at a driving voltage of approximately 15 V.
[Show abstract][Hide abstract] ABSTRACT: We report the probe of specific triplet state properties of organic chromophores that are otherwise inaccessible in low viscous solution. The prototypical example demonstrated here is [Os(CO)3(Cl)(NDP)] (1) ((NDP)H = 2-naphthyl-7-dimethylanilino-1,3-propanedione), which, upon electronic excitation, undergoes intramolecular charge transfer in both S1 and T1 manifolds of NDP. The dipolar changes in S1 and T1 monitored via the solvatochromism for both fluorescence and phosphorescence were deduced to be 18.0 and 11.9 D, respectively. The appreciable difference in the dipolar change can be qualitatively rationalized by different extents of charge-transfer character between S1 and T1 states. The results led to the probe of other reactions in triplet manifold feasible.
The Journal of Physical Chemistry B 12/2004; 108(52). DOI:10.1021/jp0453111 · 3.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Octahedral Os(II) complexes 1-5 with formula [Os(CO)3X(dbm)] are prepared through utilization of both solid-state pyrolysis and ligand exchange reactions. These complexes exhibit prominent 3pi-pi* phosphorescence with unusually long lifetimes (29-64 micros) and high quantum yields (0.08-0.13).
Chemical Communications 01/2004; DOI:10.1039/B308340C · 6.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The design and synthesis of Pd complexes with two β-ketoiminate or with two imino-alcoholate chelate ligands is reported. In order to establish their structures in the solid-state, methoxyethyl substituted complexes 1c and 2c were characterized by single crystal X-ray diffraction, showing a square-planar local coordination for the Pd atom, but the β-ketoiminate ligands of 1c gave a bent basal plane involving two chelating hexagons, which was in sharp contrast to the boat configuration of the imino-alcoholate ligands observed in the second complex 2c. Chemical vapor deposition (CVD) experiments were conducted at deposition temperatures of 250–350 °C. Scanning electron micrographs (SEM) were taken to reveal the surface morphologies and grain sizes of the Pd metal thin films. The resulting thin films were found to contain a low level of carbon and oxygen impurities using O2 as the carrier gas, as measured by X-ray photoelectron spectroscopy (XPS).
[Show abstract][Hide abstract] ABSTRACT: Reaction of Ru3(CO)12 with 6 eq. of β-diketone ligands (hfac)H, (tmhd)H, (acac)H and (tfac)H at 160–170 °C in a hydrocarbon solvent (pentane or hexane) affords the diketonate complexes [Ru(CO)2(hfac)2]
(3) and [Ru(CO)2(tfac)2]
(4) in high yields. These ruthenium complexes were characterized by spectroscopic methods; a single crystal X-ray diffraction study was carried out on one isomer of the tfac complex (4a), revealing an octahedral coordination geometry with two CO ligands located at cis-positions and with the CF3 groups of the β-diketonate ligands trans to the CO ligands. Thermogravimetric analysis of complex (1) showed an enhanced volatility compared to the parent acac complex (3), attributed to the CF3 group reducing intermolecular attraction. Employing complexes (1) and (2) as CVD source reagents, ruthenium thin films can be deposited at temperatures of 350 °C–450 °C under an H2 atmosphere or at temperatures of 275 °C–400 °C using a 2% mixture of O2 in argon as carrier gas. For deposition carried out using complex (1) and under 100% O2 atmosphere, RuO2 thin films with a preferred (200) orientation were obtained. The as-deposited thin films were characterized by surface and physical analytical techniques, such as scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction analysis (XRD) and four-point probe measurement.
[Show abstract][Hide abstract] ABSTRACT: A new metalorganic ruthenium compound which contained two β-diketonate and two CO ligands arranged in cis-disposition was used in preparation of high quality ruthenium dioxide (RuO2) thin films by cold-wall metalorganic chemical vapor deposition. A detailed characterization of the films including scanning electron microscopy (SEM), electrical resistivity, Raman scattering and X-ray diffraction measurements were carried out. The surface morphology of the films was investigated by SEM, from which a columnar growth pattern was observed using a cross-sectional scanning electron micrograph analysis. The resistivity measurement shows a metallic conducting characteristic, while Raman study indicates the formation of a high quality, nearly stress-free RuO2 film. In addition, changes of structural and electrical properties after thermal annealing are discussed.
Thin Solid Films 06/2002; 413(1-2):85-91. DOI:10.1016/S0040-6090(02)00343-7 · 1.76 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The reaction of Os3(CO)12 with 1.2 eq. of pyrazole (3,5-(CF3)2-pz)H at 190 °C affords triosmium complex Os3(CO)10(3,5-(CF3)2-pz)(μ-H)
(1) as the isolable product. Upon further treatment with excess pyrazole (3,5-(CF3)2-pz)H under more forcing conditions, complex 1 converts to a diosmium pyrazolate complex [Os(CO)3(3,5-(CF3)2-pz)]2
(2) in high yield. These osmium complexes are characterized by spectroscopic methods and single crystal X-ray diffraction study, showing the expected triangular and linear Os–Os backbone and with one and two bridging
pyrazolate ligands for complexes 1 and 2, respectively. The thermal properties are studied by TG analysis and the deposition experiments are carried out using a cold-wall CVD apparatus. The as-deposited thin films are characterized using XPS, XRD and SEM and electrical resistivity measurement. It seems that the Os metal thin films are best deposited at an optimal temperature of 450–500 °C and using complex 2 as the source reagent.