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Selected AbstractsNew Approach Toward Fast Response Light-Emitting Electrochemical Cells Based on Neutral Iridium Complexes via Cation TransportADVANCED FUNCTIONAL MATERIALS, Issue 5 2009Tae-Hyuk Kwon Abstract Here, a new method is presented to increase the turn-on time and stability of light-emitting electrochemical cells (LECs). To this end, a neutral iridium complex (5) containing a pendant Na+ ion that is generally known to have a faster mobility in the solid film than bulky anions is introduced, instead of the classic ionic transition metal complex (iTMC) with counter anion (7). Synthesis, photophysical and electrochemical studies of these complexes are reported. In the device configuration of ITO/5 or 7+PEO (polyethylene oxide) (100,110,nm)/Au, as the voltage increases, complex 5 emits red light at ,3.6,V while complex 7 appears at ,5.6,V, although their electrochemical and photophysical gap are similar. Furthermore, at constant voltage, ,3,V, the turn-on time of complex 5 was less than 0.5,min, which is a 60-fold faster turn-on time compared to the iTMC (7) with PF6,. These results are presumably due to the faster delivery of the Na+ ions to the electrode compared to PF6, ions. Also, the device lifetime of complex 5 exhibits a six-fold increase in stability and a three-fold shorter time to reach maximum brightness at constant bias compared to the device made with complex 7. [source] Electrophosphorescent Polyfluorenes Containing Osmium Complexes in the Conjugated Backbone,ADVANCED FUNCTIONAL MATERIALS, Issue 9 2008Chen-Han Chien Abstract Electrophosphorescent copolymers have been synthesized by covalent bonding of a red-emitting osmium complex Os(bpftz), which contains two 3-trifluoromethyl-5-(4- tert -butyl-2-pyridyl)triazolate (bpftz) cyclometalated ligands, into the backbone of a bipolar polyfluorene (PF) copolymer. Employing these copolymers, a highly efficient red polymer light-emitting diode has been realised that has an external quantum efficiency of 18.0%, a maximum brightness of 38,000,cd,m,2, and an emission centered at 618,nm. In addition, after incorporating appropriate amounts of green-emitting benzothiadiazole (BT) and the aforementioned Os(bpftz) into the bipolar PF, an efficient white-light electroluminescent polymer is obtained that displays simultaneous blue, green, and red emissions. [source] Rational Color Tuning and Luminescent Properties of Functionalized Boron-Containing 2-Pyridyl Pyrrolide Complexes,ADVANCED FUNCTIONAL MATERIALS, Issue 4 2005H.-Y. Chen Abstract Three systematically functionalized pyrrolide ligands were prepared via the coupling of methyl vinyl ketone and the respective carbaldehyde reagents, followed by treatment of the pre-formed dicarbonyl compounds with (NH4)2CO3 in order to generate the required pyrrole fragment. These ligands readily reacted with the boron reagent BPh3 to afford the complexes [(pyro)BPh2] (2a), [(noro)BPh2] (2b), and [(xaro)BPh2] (2c), where (pyro)H, (noro)H, and (xaro)H represents the 2-pyridyl, 2-quinolinyl, and 2-quinoxalinyl pyrrole groups, respectively. Complexes 2a,2c give stable solutions in air, and show strong photoluminescence with emission peak maxima located at 490,nm, 510,nm, and 575,nm, respectively. Calculations based upon time-dependent density function theory (TDDFT) show that the S1 state in these complexes is attributed to an allowed (,-symmetry),,,,* (,-symmetry) transition located at the chelating pyrrolide moieties. Electroluminescence (EL) devices based on 2c were fabricated. The EL emission from 2c as the host-emitter, with the emission peak maximum shifted to 580,nm, was observed when BCP was used as the hole blocking material. This device produces saturated red-orange light-emission at an onset voltage of 8,V and a maximum brightness of 5000,cd,m,2 at a driving voltage of 15,V; the external quantum yield is estimated to be 0.5,%. [source] Synthesis and characterization of the soluble fluorescent poly[2-decyloxy-5-(2,-(6,-dodecyloxy)naphthyl)-1,4-phenylenevinylene]JOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2007Hung-Te Chang Abstract A new soluble fluorescent polymer, poly[2-decyloxy-5-(2,-(6,-dodecyl-oxy)naphthyl)-1,4-phenylenevinylene] (DDN-PPV), with no tolane-bisbenzyl (TBB) structure defects is prepared by the dehydrohalogenation of 1,4-bis(bromomethyl)-2-decyloxy-5-(2,-(6,-dodecyloxy)naphthyl)benzene (as monomer) in this study. The aforementioned monomer is synthesized via such chemical reactions as alkylation, bromination, and Suzuki coupling reactions. The structure and properties of the DDN-PPV are examined by 1H NMR, FTIR, UV/vis, TGA, photoluminescence (PL), and electroluminescence (EL) analyses. The two asymmetric decyloxy and 6,-dodecyloxynaphthyl substituents on the phenylene ring make the DDN-PPV soluble in organic solvents and eliminate the TBB structure defects. With the DDN-PPV acting as a light-emitting polymer, a device is fabricated with a sequential lamination of ITO/PEDOT/DDN-PPV/Ca/Ag. The EL spectrum of the device shows a maximum emission at 538 nm. The turn on voltage of the device is about 16.6 V. Its maximum brightness is 14 cd/m2 at a voltage of 18.2 V. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2734,2741, 2007 [source] Synthesis and white electroluminescent properties of multicomponent copolymers containing polyfluorene, oligo(phenylenevinylene), and porphyrin derivativesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2009Hui Li Abstract Two novel multicomponent copolymers (P1 and P2) containing polyfluorene (PF), oligo(phenylenevinylene) (OPV), and porphyrin (Por) derivatives were synthesized according to the Suzuki polymerization method. The structures, optical, and electrochemical properties of the two model compounds (OPV and Por) and multicomponent copolymers were characterized by 1H NMR, FTIR, elemental analysis, UV,vis spectroscopy, photoluminescence, and cyclic voltammetry, respectively. Both of the copolymers exhibit thermotropic liquid crystalline properties and represent the characteristic Schlieren textures in a wide temperature range. Electroluminescence spectra of these copolymers exhibit broadband emissions covering the entire visible region from 400 to 700 nm. The single layer polymer light emitting diodes device based on P2 with a configuration of indium tin oxide/poly(ethylenedioxythiophene):poly(styrenesulfonic acid)/polymers/Ca/Al emits white light with the Commission Internationale de l,Eclairage chromaticity coordinates of (0.29, 0.30), maximum brightness of 443 cd/m2. The white-light-emitting devices based on the novel multicomponent copolymers exhibit low turn-on voltage, and good color stability at different driving voltages as well. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5291,5303, 2009 [source] PCPP derivatives containing carbazole pendant as hole transporting moiety for efficient blue electroluminescenceJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 5 2009Jinwoo Kim Abstract The syntheses and characterization of poly((2,6-(4,4-bis(4-((2-ethylhexyl)oxy)phenyl)-4H -cyclopenta[def]phenanthrene))- co -(2,6-(4,4-bis(4-(((9-carbazolyl)hexyl)oxy)phenyl))-4H- cyclopenta[def]phenanthrene)) (BCzPh-PCPPs) and poly((2,6-(4,4-bis(4-((2-ethylhexyl)oxy)phenyl)-4H -cyclopenta[def]phenanthrene))- co -(2,6-(4-(4-(((9-carbazolyl)hexyl)oxy)phenyl)-4-(4-((2-ethylhexyl)oxy)phenyl)-4H- cyclopenta[def]phenanthrene))) (CzPh-PCPPs), with carbazole unit as pendants, are presented. The carbazole moiety, which can improve the hole injection ability, was introduced as a pendant on the PCPP backbone. The devices of the polymers with the configurations of ITO/PEDOT:PSS/polymers/Ca/Al generate EL emission with maximum peaks at 400,450 nm, CIE coordinates of (x = 0.11,0.29, y = 0.11,0.33), low turn-on voltages of 4,6 V, maximum brightness of 60,810 cd/m2, and luminescence efficiencies of 0.04,0.22 cd/A. The PL spectra of CzPh-PCPPs films did not show any peak at around 550 nm, which corresponds to keto defect or aggregate/excimer formation, even after annealing for 30 h at 150 °C in air. Out of the series, CzPh-PCPP1 (PCPP derivative with 10% of carbazole moiety as pendant) shows blue emission with the maximum brightness of 810 cd/m2 at 9 V, and the highest luminescence efficiency of 0.22 cd/A at 395 mA/cm2. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1327,1342, 2009 [source] White electroluminescence from a single polyfluorene containing bis-DCM unitsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 15 2007Sang Kyu Lee Abstract A series of fluorene-based copolymers composed of blue- and orange-light-emitting comonomers were synthesized through palladium-catalyzed Suzuki coupling reactions. 9,9-Dihexylfluorene and 2-(2,6-bis-{2-[1-(9,9-dihexyl-9H -fluoren-2-yl)-1,2,3,4-tetrahydroquinolin-6-yl]-vinyl}-pyran-4-ylidene)-malononitrile (DCMF) were used as the blue- and orange-light-emitting chromophores, respectively. The resulting single polymers exhibited simultaneous blue (423/450 nm) and orange (580,600 nm) emissions from these two chromophores. By adjusting the fluorene and DCMF contents, white light emission could be obtained from a single polymer; a device with an ITO/PEDOT:PSS/polymer/Ca/Al configuration was found to exhibit pure white electroluminescence with Commission Internationale de L'Eclairage (CIE) coordinates of (0.33, 0.31), a maximum brightness of 1180 cd/m2, and a current efficiency of 0.60 cd/A. Furthermore, the white light emission of this device was found to be very stable with respect to variation of the driving voltage. The CIE coordinates of the device were (0.32, 0.29), (0.32, 0.29), and (0.33, 0.31) for driving voltages of 7, 8, and 10 V, respectively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3380,3390, 2007 [source] Phenylene vinylene-based electroluminescent polymers with electron transport block in the main chainJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2006Honghao Sun Abstract We report a new route for the design of soluble phenylene vinylene (PV) based electroluminescent polymers bearing electron-deficient oxadizole (OXD) and triazole (TZ) moieties in the main chains with the aryloxy linkage. Both series of the PV-based polymers were prepared by Wittig reaction. By properly adjusting the OXD and/or TZ content through copolymerization, we can achieve an enhanced balance of hole- and electron injections, such that the device efficiency is significantly improved. Light-emitting diodes fabricated from P1, P2, P3, P4, P5, P6, and P7 with the configuration of Indium,Tin Oxide (ITO)/Poly (styrene sulfonic acid) doped poly (ethylenedioxythiophene) (PEDOT)/polymer/Ca/Al, emit bright green light with the maximum peak around 500 nm. For the device using the optimal polymer (P4) as emitting layer, a maximum brightness of 1300 cd/m2 at 20 V and a maximum luminance efficiency of 0.325 cd/A can be obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3469,3478, 2006 [source] Homologous series of alkylsilylphenyl-substituted poly (p -phenylenevinylene)s for light-emitting diodesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2004Sung-Ho Jin Abstract Substituent-induced electroluminescence polymers,poly[2-(2-dimethyldodecylsilylphenyl)-1,4-phenylenevinylene] [(o -R3Si)PhPPV], poly[2-(3-dimethyldodecylsilylphenyl)-1,4-phenylenevinylene] [(m -R3Si)PhPPV], and poly[2-(4-dimethyldodecylsilylphenyl)-1,4-phenylenevinylene] [(p -R3Si)PhPPV],were synthesized according to the Gilch polymerization method. The band gap and spectroscopic data were tuned by the dimethyldodecylsilyl substituent being changed from the ortho position to the para position in the phenyl side group along the polymer backbone. The weight-average molecular weights and polydispersities were 8.0,96 × 104 and 3.0,3.4, respectively. The maximum photoluminescence wavelengths for (o -R3Si)PhPPV, (m -R3Si)PhPPV, and (p -R3Si)PhPPV appeared around 500,530 nm in the green emission region. Double-layer light-emitting diodes with an indium tin oxide/poly(3,4-ethylenedioxythiophene)/polymer/Al configuration were fabricated with these polymers. The turn-on voltages and the maximum brightness of (o -R3Si)PhPPV, (m -R3Si)PhPPV, and (p -R3Si)PhPPV were 6.5,8.7 V and 1986,5895 cd/m2, respectively. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2347,2355, 2004 [source] Discovery of cyclic spot activity on the G8 giant HD 208472,ASTRONOMISCHE NACHRICHTEN, Issue 8 2010O. Özdarcan Abstract We present and analyze 17 consecutive years of UBVRI time-series photometry of the spotted giant component of the RS CVn binary HD 208472. Our aim is to determine the morphology and the evolution of its starspots by using periodsearch techniques and two-spot light-curve modelling. Spots on HD208472 always occur on hemispheres facing the observer during orbital quadrature and flip their location to the opposite hemisphere every approximately six years. The times when the spots change their preferential hemisphere correspond to times when the light curve amplitudes are the smallest and when abrupt changes of the photometric periods are observed. During these times the star is also close to a relative maximum brightness, suggesting a vanishing overall spottedness at each end of the previous cycle and the start of a new one. We find evidence for a 6.28±0.06-yr brightness cycle, which we interpret to be a stellar analog of the solar 11-year sunspot cycle. We also present clear evidence for a brightening trend, approximated with a 21.5±0.5-yr period, possibly due to a stellar analog of the solar Gleissberg cycle. From the two-spot modelling we also determine an upper limit for the differential-rotation coefficient of , = ,P/P of 0.004±0.010, which would be fifty times weaker than on the Sun (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] New absolute magnitude calibrations for WUrsa Majoris type binariesASTRONOMISCHE NACHRICHTEN, Issue 1 2009Z. Eker Abstract Parallaxes of W UMa stars in the Hipparcos catalogue have been analyzed. 31 W UMa stars, which have the most accurate parallaxes (,, /, < 0.15) which are neither associated with a photometric tertiary nor with evidence of a visual companion, were selected for re-calibrating the Period-Luminosity-Color (PLC) relation of W UMa stars. Using the Lutz-Kelker (LK) bias corrected (most probable) parallaxes, periods (0.26 < P < 0.87, P in days), and colors (0.04 < (B , V)0 < 1.28) of the 31 selected W UMa, the PLC relation have been revised and re-calibrated. The difference between the old (revised but not bias corrected) and the new (LK bias corrected) relations are almost negligible in predicting the distances of W UMa stars up to about 100 pc. But, it increases and may become intolerable as distances of stars increase. Additionally, using (J , H)0 and (H , Ks)0 colors from 2MASS (TwoMicron All Sky Survey) data, a PLC relation working with infrared data was derived. It can be used with infrared colors in the range ,0.01 < (J , H)0 < 0.58, and ,0.10 < (H , Ks)0 < 0.18. Despite of the fact that the 2MASS data refer to single epoch observations which are not guaranteed to be taken at maximum brightness of theWUMa stars, the established relation has been found surprisingly consistent and reliable in predicting LK corrected distances of W UMa stars (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Asymmetrical Fluorene[2,3- b]benzo[d]thiophene Derivatives: Synthesis, Solid-State Structures, and Application in Solution-Processable Organic Light-Emitting DiodesCHEMISTRY - A EUROPEAN JOURNAL, Issue 33 2009Chunyan Du Abstract A series of novel asymmetrical fused compounds containing the backbone of fluorene[2,3- b]benzo[d]thiophene (FBT) were effectively synthesized and fully characterized. Single-crystal X-ray studies demonstrated that the length of the substituent side chains greatly affects the solid-state packing of the obtained fused compounds. DFT, photophysical, and electrochemical studies all showed that the FBTs have large band gaps, low-lying HOMO energy levels, and therefore good stability toward oxidation. Moreover, the substituents strongly influence the fluorescence properties of the resulting FBT derivatives. The di- n -hexyl compound exhibits intense fluorescence in solution with the highest quantum yield of up to 91,%. Solution-processed green phosphorescent organic light-emitting diodes with the di- n -butyl derivative as the host material exhibited a maximum brightness of 14,185,cd,m,2 and a luminescence efficiency of 12,cd,A,1. [source] | ||||||||||