Browsing by Author "Cheng, Yi-Ming"

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Bis(diphenylamino)-9,9 '-spirobifluorene functionalized Ir(III) complex: a conceptual design en route to a three-in-one system possessing emitting core and electron and hole transport peripherals
(2011)
Chen, Hsiao-Fan
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Wong, Ken-Tsung
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Liu, Yi-Hung
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Wang, Yu
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Cheng, Yi-Ming
Conceptual design of a three-in-one (luminescence chromophore with electron and hole transports) system was demonstrated by a functionalized Ir(III) complex 3, in which 4,5-diazafluorene and bis(diphenylamino) serve as electron and hole transporting sites, respectively. The poor emission quantum yield of 3 was systematically examined via a series of photophysical studies in combination with theoretical approaches. The far lifting of the pi-electron from -NPh(2) renders virtually no (3)MLCT contribution to the lowest transition in the triplet manifold as compared with that of the parent model 2 without amino substituents. With an empirical approach, we conclude that an energy gap law may account for the major deactivation process. A light-emitting electrochemical cell (LEC) device based on 3 shows peak EQE, peak current efficiency and peak power efficiency at 2.4 V of 0.020%, 0.013 cd A(-1) and 0.017 lm/W, respectively. The low device efficiencies are in accordance with the low PL quantum yield, stemming from the ligand-centered radiationless deactivation. The conceptual design presented here should provide valuable information for future progress en route to an ideal three-in-one system suited for OLEDs.
New Series of Ruthenium(II) and Osmium(II) Complexes Showing Solid-State Phosphorescence in Far-Visible and Near-Infrared
(2010-02-01)
Chen, Jing-Lin
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Chi, Yun
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Chen, Kellen
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Cheng, Yi-Ming
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Chung, Min-Wen
A new Ru(II) complex, [Ru(fpbpymH)(2)]Cl(2) (1), in which fpbpymH = [5-(trifluoromethyl)pyrazol-3-yl](2,2'-bipyrid-6-yl)methane, was prepared by the treatment of [Ru(DMSO)(4)Cl(2)] with 2 equiv of the terdentate chelate fpbpymH in refluxing ethanol. A single-crystal X-ray diffraction study of 1 revealed a distorted octahedral Ru(II) framework, showing strong N-H center dot center dot center dot Cl hydrogen bonding between the fpbpymH ligand and Cl anions. In the presence of Na(2)CO(3), the methylene linkers of chelates in 1 underwent stepwise oxygenation, forming the charge-neutral complexes [Ru(fpbpym)(fpbpyk)] (2) and [Ru(fpbpyk)(2)] (3) [fpbpykH = [5-(trifluoromethyl)pyrazol-3-yl](2,2'-bipydd-6-yl) ketone] in sequence. The respective charge-neutral Os(II) complex [Os(fpbpyk)(2)] (4) was also isolated by the treatment of OsCl(3)center dot 3H(2)O with 2 equiv of the terdentate chelate fpbpymH, Electrochemical analysis indicated that the introduction of the electron-withdrawing ketone group in 2-4 increased the metal-based oxidation potential in sequence. For the photophysical properties, complexes 1-4 are essentially nonluminescent in solution (e.g., CH(2)Cl(2) or MeOH) at room temperature, but all exhibit 600-1100 nm phosphorescence with moderate intensity for the powdery, solid sample at room temperature. The trend in terms of the emission peak wave ength of 1 (666 nm) < 3 (795 nm) < 2 (810 nm) < 4 (994 nm) among titled complexes is in agreement with the corresponding onset of absorption spectra as well as the time-dependent density functional theory calculation of 1 < 3 < 2 < 4.
Orange and red organic light-emitting devices employing neutral Ru(II) emitters: Rational design and prospects for color tuning
(2006-08-04)
Tung, Yung-Liang
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Chen, Li-Shiuan
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Chi, Yun
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Chou, Pi-Tai
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Cheng, Yi-Ming
A new series of charge-neutral Ru(II) pyridyl and isoquinoline pyrazolate complexes, [Ru(bppz)(2)(PPh2Me)(2)] (bbpz: 3-tert-butyl-5-pyridyl pyrazolate) (1), [Ru(fppz)(2)(PPh2Me)(2)] (fppz: 3-trifluoromethyl-5-pyridyl pyrazolate) (2), [Ru(ibpz)(2)(PPhMe2)(2)] (ibpz: 3-tert-butyl-5-(1-isoquinolyl) pyrazolate) (3), [Ru(ibpz)(2)(PPh2Me)(2)] (4), [Ru(ifpz)(2)(PPh2Me)(2)] (ifpz: 3-trifluoromethyl-5-(1-isoquinolyl) pyrazolate) (5), [Ru(ibpz)(2)(dpp=)] (dpp= represents cis-1,2-bis-(diphenylphosphino)ethene) (6), and [Ru(ifpz)(2)(dpp=)] (7), have been synthesized, and their structural, electrochemical, and photophysical properties have been characterized. A comprehensive time-dependant density functional theory (TDDFT) approach has been used to assign the observed electronic transitions to specific frontier orbital configurations. A multilayer organic light-emitting device (OLED) using 24 wt % of 5 as the dopant emitter in a 4,4'-N,N'-dicarbazolyl-1,1'-biphenyl (CBP) host with 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB) as the hole-transport layer exhibits saturated red emission with an external quantum efficiency (EQE) of 5.10%, luminous efficiency of 5.74 cd A(-1), and power efficiency of 2.62 lm W-1. The incorporation of a thin layer of poly(styrene sulfonate)-doped poly(3,4-ethylenedioxythiophene) (PEDOT) between indium tin oxide (ITO) and NPB gave anoptimized device with an EQE of 7.03%, luminous efficiency of 8.02 cd A(-1), and power efficiency of 2.74 lm W-1 at 20 mA cm(-2). These values represent a breakthrough in the field of OLEDs using less expensive Ru(II) metal complexes. The nonionic nature of the complexes as well as their high emission quantum efficiencies and short radiative lifetimes are believed to be the key factors enabling this unprecedented achievement. The prospects for color tuning based on Ru(II) complexes are also discussed in light of some theoretical calculations.
Pt(II) Complexes with 6-(5-Trifluoromethyl-Pyrazol-3-yl)-2,2 '-Bipyridine Terdentate Chelating Ligands: Synthesis, Characterization, and Luminescent Properties
(2008-01-01)
Chen, Jing-Lin
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Chang, Sheng-Yuan
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Chi, Yun
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Chen, Kellen
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Cheng, Yi-Ming
A series of Pt(II) complexes Pt(fpbpy)Cl (1), Pt(fpbpy)(OAc) (2), Pt(fpbpy)(NHCOMe) (3), Pt(fpbpy)(NHCOEt) (4), and [Pt(fpbpy)(NCMe)](BF(4)) (5) with deprotonated 6-(5-trifluoromethyl-pyrazol-3-yl)-2,2'-bipyridine terdentate ligand are prepared, among which 1 is converted to complexes 2-5 by a simple ligand substitution. Alternatively, acetamide complex 3 is prepared by hydrolysis of acetonitrile complex 5, while the back conversion from 3 to 1 is regulated by the addition of HCl solution, showing the reaction sequence 1 -> 5 -> 3 -> 1. Mullilayer OLED devices are successfully fabricated by using triphenyl-(4-(9-phenyl-9H-fluoren-9-yl)phenyl) silane (TPSi-F) as host material and with doping concentrations of 1 varying from 7 to 100%. The electroluminescence showed a substantial red-shifting versus the normal photoluminescence detected in solution. Moreover, at a doping concentration of 28%, the device showed a saturated red luminescence with a maximum external quantum yield of 8.5% at 20 mA cm(-2) and a peak luminescence of 47543 cd m(-2) at 18.5 V.
Pt-II Complexes with 6-(5-Trifluoromethyl-Pyrazol-3-yl)-2,2 '-Bipyridine Terdentate Chelating Ligands: Synthesis, Characterization, and Luminescent Properties
(2008-01-01)
Chen, Jing-Lin
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Chang, Sheng-Yuan
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Chi, Yun
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Chen, Kellen
;
Cheng, Yi-Ming
A series of Pt-II complexes Pt(fpbpy)Cl (1), Pt(fpbpy)(OAc) (2), Pt(fpbpy)(NHCOMe) (3), Pt(fpbpy)(NHCOEt) (4), and [Pt(fpbpy)(NCMe)](BF4) (5) with deprotonated 6-(5-trifluoromethyl-pyrazol-3-yl)-2,2'-bipyridine terdentate ligand are prepared, among which 1 is converted to complexes 2-5 by a simple ligand substitution. Alternatively, acetamide complex 3 is prepared by hydrolysis of acetonitrile complex 5, while the back conversion from 3 to 1 is regulated by the addition of HCl solution, showing the reaction sequence 1 -> 5 -> 3 -> 1. Mullilayer OLED devices are successfully fabricated by using triphenyl-(4-(9-phenyl-9H-fluoren-9-yl)phenyl) silane (TPSi-F) as host material and with doping concentrations of 1 varying from 7 to 100%. The electroluminescence showed a substantial red-shifting versus the normal photoluminescence detected in solution. Moreover, at a doping concentration of 28%, the device showed a saturated red luminescence with a maximum external quantum yield of 8.5% at 20 mA cm(-2) and a peak luminescence of 47543 cd m(-2) at 18.5 V.
Strategic design and synthesis of osmium(II) complexes bearing a single pyridyl azolate pi-chromophore: Achieving high-efficiency blue phosphorescence by localized excitation
(2007-11-26)
Cheng, Yi-Ming
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Li, Elise Y.
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Lee, Gene-Hsiang
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Chou, Pi-Tai
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應用化學系
We present the strategic design and synthesis of Os(II) complexes bearing a single pyridyl azolate T-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)T-chromophore on the Os(II) complexes such that the control of MLCT versus pi pi* (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 (lambda(max) = 460 nm) and 0.27 (lambda(max) = 450 nm), respectively. For their halide analogues [Os(CO)(3)(X)(fppz)] (2, X = Cl; 3, X Br; 4, X = 1) and phosphine-substituted isomeric derivatives [Os(tfa)(fppz)(PPh(2)Me)(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.
Syntheses, Photophysics, and Application of Iridium(III) Phosphorescent Emitters for Highly Efficient, Long-Life Organic Light-Emitting Diodes
(2009)
Lee, Tsang-Chi
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Chang, Chiung-Fang
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Chiu, Yuan-Chieh
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Chi, Yun
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Chan, Tzu-Ying
Rational design and synthesis of Ir(III) complexes (1-3) bearing two cyclometalated ligands (C boolean AND N) and one 2-(diphenylphosphino)phenolate chelate (P boolean AND O) as well as the corresponding Ir(III) derivatives (4-6) with only one (C boolean AND N) ligand and two P boolean AND O chelates are reported, where (C boolean AND NH) = phenylpyridine (ppyH), 1-phenylisoquinoline (piqH), and 4-phenylquinazoline (nazoH). Single crystal X-ray diffraction studies of 3 reveal a distorted octahedral coordination geometry. in which two nazo ligands adopt an eclipsed Configuration, with the third P boolean AND O ligand located trans to the phenyl group of both nazo ligands, confirming the general skeletal pattern for 1-3. In sharp contrast, complex 4 reveals a trans-disposition for the PPh(2) groups, along with the phenolate groups residing opposite the unique cyclometalated ppy ligand, which is the representative structure for 4-6. These Ir(III) complexes exhibit green-to-red photoluminescence with moderate to high quantum efficiencies in the degassed fluid state and bright emission in the solid state. For 1-6, the resolved emission spectroscopy and relaxation dynamics are well rationalized by the Computational approach. OLEDs fabricated using 12 wt.% of 3 doped in CBP and with BCP as hole blocking material, give bright electroluminescence with lambda(max) = 628 nm and CIE(xy) coordinates (0.65, 0.34). The turn-on voltage is 3.2 V, while the current efficiency and the power efficiency reach 11.2cd A(-1) and 4.5 lm W(-1) at 20 mA cm(-2). The maximum efficiency reaches 14.7 cd A(-1) and 6.8 lm W(-1) upon switching to TPBI as hole blocking material. For evaluating device lifespan, the tested device incorporating CuPc as a passivation layer, 3 doped in CTP as an emitting layer, and BAlq as hole blocking material, shows a remarkably long lifetime up to 36 000 h at an initial luminance of 500 cd m(-2).