Browsing by Author "Chen, Kellen"

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Color tuning associated with heteroleptic cyclometalated Ir(III) complexes: influence of the ancillary ligand
(2007)
Chang, Chau-Jiun
;
Yang, Cheng-Han
;
Chen, Kellen
;
Chi, Yun
;
Shu, Ching-Fong
We report the preparation of a series of new heteroleptic Ir(III) metal complexes chelated by two cyclometalated 1-(2,4-difluorophenyl) pyrazole ligands (dfpz)H and a third ancillary bidentate ligand ( L. X). Such an intricate design lies in a core concept that the cyclometalated dfpz ligands always warrant a greater pi pi* gap in these series of iridium complexes. Accordingly, the lowest one-electron excitation would accommodate the pi* orbital of the ancillary L(boolean AND)X ligands, the functionalization of which is then exploited to fine-tune the phosphorescent emission wavelengths. Amongst the L. X ligands designed, three classes (series 1-3) can be categorized, and remarkable bathochromic shifts of phosphorescence were observed by (i) replacing the 2-benzoxazol-2-yl-substituent (1a) with the 2-benzothiazol-2-yl group (1b) in the phenolate complexes, (ii) converting the pyridyl group (2a) to the pyrazolyl group (2b) and even to the isoquinolyl group (2c) in the pyrazolate complexes and (iii) extending the pi-conjugation of the benzimidazolate ligand from 3a to 3b. Single-crystal X-ray diffraction study on complex [(dfpz)Ir(bzpz)] (2b) was conducted to confirm their general molecular architectures. Complex 2b was also used as a representative example for fabrication of multilayered, green-emitting phosphorescent OLEDs using the direct thermal evaporation technique.
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
;
Chi, Yun
;
Chen, Kellen
;
Cheng, Yi-Ming
;
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.
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
;
Chang, Sheng-Yuan
;
Chi, Yun
;
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)](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
;
Chang, Sheng-Yuan
;
Chi, Yun
;
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.