Kang-Wei Wang

Tamkang University, T’ai-pei, Taipei, Taiwan

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Publications (5)29.65 Total impact

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    ABSTRACT: The synthesis of a new family of octahedral Ir(III) complexes with dual cyclometalating phosphine chelates, namely: 1-(diphenylphosphino)naphthalene (dpnaH) and isoquinoline (dppiH), is reported. Two series of intermediate complexes, [Ir(dpna)(tht)(2)Cl(2)] (1), [Ir(dpna)(2)(OAc)] (2), [Ir(dppiH)(dppi)Cl(2)] (3) and [Ir(dppi)(2)(OAc)] (4), which can be classified by the coexistence of either a pair of cis-chlorides or a single acetate chelate, were obtained from treatment of phosphine with [IrCl(3)(tht)(3)] (tht = tetrahydrothiophene). The in situ generated acetate complexes 2 and 4 could react with azolate chelates, namely: 5-(2-pyridyl)-3-trifluoromethyl pyrazole (fppzH) and 5-(1-isoquinolyl)-3-tert-butyl-1,2,4-triazole (iqbtzH), to afford a new series of luminescent complexes [Ir(dpna)(2)(fppz)] (5a and 5b), [Ir(dpna)(2)(iqbtz)] (6a and 6b), [Ir(dppi)(2)(fppz)] (7a) and [Ir(dppi)(2)(iqbtz)] (8a). The phosphorescence lifetime (τ(obs)) fell in the range of a few tens of μs, showing possession of excessive ligand-centered ππ* mixed in part with MLCT character. A density functional theory (DFT) study was also conducted in order to shed light on the origin of the transitions in the absorption and emission spectra and to predict emission energies for these complexes. Organic light emitting diodes (OLEDs) displaying bright orange emission and with maximum η(ext) up to 17.1% were fabricated employing complexes 6a and 8a as the phosphorescent dopants.
    Dalton Transactions 02/2011; 40(5):1132-43. · 4.10 Impact Factor
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    ABSTRACT: A series of new mesomorphic platinum(II) complexes 1-4 bearing pyridyl pyrazolate chelates are reported herein. In this approach, pyridyl azolate ligands have been strategically functionalized with tris(alkoxy)phenyl groups with various alkyl chain lengths. As a result, they are ascribed to a class of luminescent metallomesogens that possess distinctive morphological properties, such as their intermolecular packing arrangement and their associated photophysical behavior. In CH(2) Cl(2), independent of the applied concentration in the range 10(-6)-10(-3)  M, all Pt(II) complexes exhibit bright phosphorescence centered at around 520 nm, which is characteristic for monomeric Pt(II) complexes. In stark contrast, the single-crystal X-ray structure determination of [Pt(C4pz)(2)] (1) shows the formation of a dimeric aggregate with a notable Pt⋅⋅⋅Pt contact of 3.258 Å. Upon heating, all Pt(II) complexes 1-4 melted to form columnar suprastructures, for which similar intracolumnar Pt⋅⋅⋅Pt distances of approx. 3.4-3.5 Å are observed within an exceptionally wide temperature range (>250 °C), according to the powder XRD data. Upon casting into a neat thin film at RT, the luminescence of 1-4 is dominated by a red emission that spans 630-660 nm, which originates from the one-dimensional, chainlike structure with Pt-Pt interaction in the ground state. Taking complex 4 as a representative, the emission intensity and wavelength were significantly decreased and blueshifted, respectively, on heating from RT to 250 °C. Further heating to liquefy the sample alters the red emission back to the green phosphorescence of the monomer. The results highlight the pivotal role of tris(alkoxy)phenyl groups in the structural versus luminescence behavior of these Pt(II) complexes.
    Chemistry - A European Journal 01/2011; 17(2):546-56. · 5.93 Impact Factor
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    ABSTRACT: A series of charge-neutral mononuclear Pt(II) complexes Pt(fpbpy)(pz) (3a), Pt(fpbpy)(dmpz) (4a), Pt(fpbpy)(dbpz) (5a), and Pt(fpbpy)(dtfpz) (6a), fpbpyH = 6-(5-trifluoromethyl-pyrazol-3-yl)-2,2'-bipyridine, pzH = pyrazole, dmpzH = 3,5-dimethylpyrazole, dbpzH = 3,5-di-tert-butylpyrazole, and dtfpzH = 3,5-bis(trifluoromethyl)pyrazole, and the cationic Pt(II) dimer [{Pt(fpbpy)}(2)(mu-pz)](+) (3b), [{Pt(fpbpy)}(2)(mu-dmpz)](+) (4b), and [{Pt(fpbpy)}(2)(mu-dbpz)](+) (5b) were synthesized. Series a mononuclear complexes reveal two distinctive ligand arrangements. As unveiled by X-ray crystallography, 3a exhibits a nearly perfect planar geometry, while structural determination on 6a shows a perpendicular arrangement of dbpz ligand due to steric congestion. In sharp contrast, the dinuclear complexes, exemplified by 4b and 5b, display an intramolecular Pt...Pt separation of 3.601 and 3.403 A, respectively. As for photophysical properties, the structural variation leads to a salient difference in emission features between 3a (580 nm) and 6a (510 nm). The results are rationalized by the contribution of ligand-to-ligand charge transfer and intraligand pi-pi* transition for 3a and 6a in the lowest-lying excited state, respectively. On the other hand, dinuclear complexes 3b and 4b reveal dual phosphorescence (denoted as P(1) and P(2) bands), for which the short wavelength emission (the P(1) band) is akin to that observed for the intraligand pi-pi* transition of 6a, while the much red-shifted, broad emission (the P(2) band) is attributed to the formation of intramolecular ligand-metal-to-metal charge transfer excimer transition. Further studies of relaxation dynamics on both 3b and 4b showed fast excited-state equilibrium between the P(1) and P(2) bands. In contrast, only the P(2) emission band was resolved for 5b, indicating its exergonic excimer formation. Supplementary support of the excited-state thermodynamics is also provided by time-dependent density functional theory calculations, incorporating both geometry optimized S(0) and T(1) states.
    Inorganic Chemistry 02/2010; 49(4):1372-83. · 4.59 Impact Factor
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    ABSTRACT: Sequential treatment of IrCl(3) x nH(2)O with 2 equiv of benzyl diphenylphosphine (bdpH) and then 1 equiv of 3-trifluoromethyl-5-(2-pyridyl) pyrazole (fppzH) in 2-methoxyethanol gave formation to three isomeric complexes with formula [Ir(bdp)(fppz)(bdpH)H] (1-3). Their molecular structures were established by single crystal X-ray diffraction studies, showing existence of one monodentate phosphine bdpH, one terminal hydride, a cyclometalated bdp chelate, and a fppz chelate. Variation of the metal-ligand bond distances showed good agreement with those predicted by the trans effect. Raman spectroscopic analyses and the corresponding photophysical data are also recorded and compared. Among all isomers complex 1 showed the worst emission efficiency, while complexes 2 and 3 exhibited the greatest luminescent efficiency in solid state and in degassed CH(2)Cl(2) solution at room temperature, respectively. This structural relationship could be due to the simultaneously weakened hydride and the monodentate bdpH bonding that are destabilized by the trans-pyrazolate anion and cyclometalated benzyl group, respectively.
    Inorganic Chemistry 09/2009; 48(17):8164-72. · 4.59 Impact Factor
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    ABSTRACT: Highly efficient blue electrophosphorescent organic light-emitting diodes incorporating a bipolar host, 2,7-bis(diphenylphosphoryl)-9-[4-(N,N-diphenylamino)phenyl]-9-phenylfluorene (POAPF), doped with a conventional blue triplet emitter, iridium(III) bis[(4,6-difluoro-phenyl)pyridinato-N,C2´]picolinate (FIrpic) are fabricated. The molecular architecture of POAPF features an electron-donating (p-type) triphenylamine group and an electron-accepting (n-type) 2,7-bis(diphenyl-phosphoryl)fluorene segment linked through the sp3-hybridized C9 position of the fluorene unit. The lack of conjugation between these p- and n-type groups endows POAPF with a triplet energy gap (ET) of 2.75 eV, which is sufficiently high to confine the triplet excitons on the blue-emitting guest. In addition, the built-in bipolar functionality facilitates both electron and hole injection. As a result, a POAPF-based device doped with 7 wt% FIrpic exhibits a very low turn-on voltage (2.5 V) and high electroluminescence efficiencies (20.6% and 36.7 lm W−1). Even at the practical brightnesses of 100 and 1000 cd m−2, the efficiencies remain high (20.2%/33.8 lm W−1 and 18.8%/24.3 lm W−1, respectively), making POAPF a promising material for use in low-power-consumption devices for next-generation flat-panel displays and light sources.
    Advanced Functional Materials 07/2009; 19(17):2834 - 2843. · 10.44 Impact Factor

Publication Stats

27 Citations
29.65 Total Impact Points

Institutions

  • 2011
    • Tamkang University
      T’ai-pei, Taipei, Taiwan
  • 2010–2011
    • National Taiwan University
      • Department of Chemistry
      T’ai-pei, Taipei, Taiwan
  • 2009
    • National Tsing Hua University
      • Department of Chemistry
      Hsinchu, Taiwan, Taiwan