Yazar "Demic, Serafettin" seçeneğine göre listele

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    A new conducting polymer of 2,5-bis(2-thienyl)-1H-(pyrrole) (SNS) containing carbazole subunit: Electrochemical, optical and electrochromic properties
    (Elsevier Science Sa, 2009) Koyuncu, Sermet; Zafer, Ceylan; Sefer, Emre; Koyuncu, Fatma Baycan; Demic, Serafettin; Kaya, İsmet; Ozdemir, Eyup
    We report here the synthesis of a new electroactive monomer 3,6-di-tert-butyl-[4-(2,5-di-2-thienyl-1H-pyrrol-1-yl)phenyl]-9H-carbazole in five steps and polymerization of this monomer by two different procceses: Kumada Coupling and electro-oxidative. The product obtained by chemical polymerization exhibits a high thermal stability and narrow molecular weight distribution. While, in the UV-vis absorption spectrum of monomer the absorption peaks appear at 338 nm, the chemically synthesized polymer absorbs at 428 nm with 90 nm red shift. Cyclic voltammogram of monomer shows two separate oxidation processes which reflect the first oxidation at +0.84 V and a second one at +1.43 V. When the polymeric film prepared by electrochemical process was subjected to a repeated cyclic scan between -0.2V and +1.0V, it switches among three different colors (orange, green and blue). The oxidation and reduction response times were calculated as 2.0 s for this polymer film and exhibits high redox stability. The results anticipate that this kind of polymers can be used for designing electrochromics based on the use of one molecule for the generation of three basic colors (RGB). (C) 2009 Elsevier B.V. All rights reserved.
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    A Novel High-Contrast Ratio Electrochromic Material from Spiro[cyclododecane-1,9?-fluorene]bicarbazole
    (Wiley-Blackwell, 2011) Usluer, Ozlem; Koyuncu, Sermet; Demic, Serafettin; Janssen, Rene A. J.
    A novel electroactive spirocyclododecylfluorene monomer named 2,7-bis(carbazol-9-yl)-9,9'-spiro[cyclododecane- 1,9'-fluorene] (SFC) was synthesized and electrochemically polymerized to give a very stable multi-electrochromic polymer (poly-SFC). Two separate oxidation processes were observed for both SFC monomer and poly-SFC that carries two carbazole units. The polymeric film of poly-SFC was coated onto ITO/glass surface, and it shows different colors (transparent, yellowish green, green, and dark green) upon stepwise oxidations. An electrochromic device based on poly-SFC was assembled in the sandwich cell configuration of ITO/poly-SFC// gel electrolyte//PEDOT/ITO. Poly-SFC exhibits 90% of transparency at neutral state and a high contrast ratio (Delta T = 58% at 800 nm). This device constructed from it represents a response time of about 1 s, high coloration efficiency (1377 cm(2) C-1) and retained its performance by 96.4% even after 1000 cycles. Exhibiting high transparency at neutral state, reversible redox behavior, resistance to overoxidation, and especially high contrast ratio at near IR region can make poly-SFC be useful and promising candidate for electrochromic applications despite having a relatively slow response time. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 333-341, 2011
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    Effect of a pi-bridging unit in triphenylamine-benzothiadiazole based donor acceptor chromophores for dye-sensitized solar cells
    (Pergamon-Elsevier Science Ltd, 2014) Yigit, Mesude Zeliha; Bilgili, Hakan; Sefer, Emre; Demic, Serafettin; Zafer, Ceylan; Can, Mustafa; Koyuncu, Sermet
    Two new metal free sensitizers based on triphenylamine-benzothiadiazole were synthesized and used in dye sensitized solar cells (DSSCs). Electrochemical and optical properties of the dyes were studied by cyclic voltammetry, UV-vis absorption and fluorescence spectroscopy. A red shift was observed by the attachment of a thiophene (MZ-259) instead of a phenylene (MZ-255) bridge. The reverse effect was observed in the electrochemical properties because of the more electron-donating thiophene incorporated into the cyanoacrylic acid as an anchoring-acceptor unit in this system resulted in a higher LUMO level. The charge distribution of the dyes was also proved by DFT calculations using the Spartan10 program with the parameters of B3LYP and 6-31G** basis set. Finally the photovoltaic performances were investigated under standard AM 1.5 illumination with a power of 100 mW/cm(2) using an ionic liquid based electrolyte. The power conversion efficiencies, eta, were increased from 3.16% to 3.81% by using thiophene instead of phenylene as a pi-bridge unit. (C) 2014 Elsevier Ltd. All rights reserved.
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    Electrochemical and optical properties of biphenyl bridged-dicarbazole oligomer films: Electropolymerization and electrochromism
    (Pergamon-Elsevier Science Ltd, 2009) Koyuncu, Sermet; Gultekin, Burak; Zafer, Ceylan; Bilgili, Hakan; Can, Mustafa; Demic, Serafettin; Kaya, İsmet
    4,4'-Di(N-carbazoyl)biphenyl monomer (CBP) was synthesized and coated onto ITO-glass surface by electrochemical oxidative polymerization. Its CV shows two distinct one-electron and stepwise oxidation processes occurred at 1.29 and 1.61 V. By using this property, the monomer was electrochemically polymerized separately at these oxidation states and thus, two different oligomer films were obtained afterwards. Their spectro-electrochemical and electrochromic properties were also investigated. Switching ability of the oligomers was evaluated by kinetic studies upon measuring the percent transmittance (%T) at their maximum contrast point, indicating that these oligomers were found to be suitable material for electrochromic devices. (C) 2009 Elsevier Ltd. All rights reserved.
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    Electrochemical and optical properties of novel donor-acceptor thiophene-perylene-thiophene polymers
    (Wiley, 2008) Koyuncu, Sermet; Kus, Mahmut; Demic, Serafettin; Kaya, İsmet; Ozdemir, Eyup; Icli, Siddik
    In this study, donor-acceptor type thiophene-perylene-thiophene monomers were synthesized and polymerized by both oxidative polymerization using FeCl3 as catalyst and the electrochemical process. UV-vis, FTIR, H-1 NMR, and elemental analysis techniques were used for structural characterization. Thermal behaviors of these compounds were determined by using TGA system. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels and electrochemical and optical band gap values were calculated by using the results of cyclic voltammetry and UV-vis measurements, respectively. The number-average molecular weight (M-n), weight-average molecular weight (M-n), and polydispersity index (PDI) values of synthesized polymers were determined by size exclusion chromatography. Conductivity measurements of these polymers were carried out by electrometer by using a four-point probe technique. The conductivity was observed to be increased by iodine doping. (C) 2008 Wiley Periodicals, Inc.
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    Electrochromic and electroluminescent devices based on a novel branched quasi-dendric fluorene-carbazole-2,5-bis(2-thienyl)-1H-pyrrole system
    (Royal Soc Chemistry, 2011) Koyuncu, Sermet; Usluer, Ozlem; Can, Mustafa; Demic, Serafettin; Icli, Siddik; Sariciftci, Niyazi Serdar
    We report here the synthesis of a novel branched quasi-dendric system, 9,9'-(9,9'-dihexylfluorene-2,7-diyl)bis[3,6-bis(2,5-bis(2-thienyl) pyrrol-1-yl)carbazole], (FCSNS), in four steps, followed by coating onto an ITO-coated glass surface by an electropolymerization process to give a very stable cross-linked polymeric film (poly-FCSNS). The yellowish-green color of this film in its neutral state changed reversibly to black upon oxidation. An electrochromic device, assembled in the sandwich configuration [ITO/anodically coloring polymer (poly-FCSNS)//gel electrolyte//cathodically coloring polymer/(PEDOT)/ITO], exhibited a relatively short response time (about 1 s), a high redox stability, and a high coloration efficiency (1624 cm(2) C-1). In addition to electrochromic studies, organic light-emitting diode (OLED) work was also carried out using FCSNS. A multilayer OLED having a configuration of ITO/PEDOT:PSS/FCSNS/Alq(3)/LiF : Al was fabricated, and it showed a turn-on voltage of approximately 6 V and exhibited a bright green emission with a luminance of 3700 cd m(-2). The maximum luminous efficiency was found to be 2.0 cd A(-1) at 14 V and 11.75 mA cm(-2). The emitted light from the OLED device is green, and has the color coordinates of (x, y) (0.33, 0.54) according to CIE. Electrochemical and optical properties were also studied by using cyclic voltammetry, UV-Vis absorption and fluorescence spectroscopy, respectively.
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    Electroluminescence performance of a series of fluorene/2,5-di(2-thienyl)-1H-pyrrole polymers
    (Wiley, 2020) Bilgili, Hakan; Kara, Koray; Yenel, Esma; Demic, Serafettin; Kus, Mahmut; Koyuncu, Sermet
    In this article, a series of fluorene/2,5-dithenyl-1H-pyrrole-based electroactive polymers (HS-X) with different feed ratio of SC12F/OF were synthesized via Suzuki coupling reactions. Chemical characterization of polymers was elucidated by(1)H NMR and Fourier-transform infrared spectroscopy. Electrochemical and electrophysical characterization of the synthesized polymers were investigated by cyclic voltammetry, UV-vis spectroscopy, and fluorescence spectroscopy. Thermal stability of polymers were studied with differential scanning calorimetry and manipulation of the Tg values of HS-X polymers was managed by increasing the numbers of the spiroalkylated fluorene (SAF) moieties incorporated into the polymer backbone. Five different conjugated polymers (HS-1, HS-2, HS-3, HS-4, and HS-5) were used as hole transport layer material in the fabrication of organic light-emitting diode (OLED) devices. The energy levels of the highest occupied molecular orbital as well as the lowest unoccupied molecular orbital and photoluminescence intensities were independent of the number of SAF units. OLED devices based on HS-X polymers were fabricated according to ITO/PEDOT:PSS/HS-X/Alq3/LiF:Al device configuration. Their electroluminescence performances were investigated and the best performance were obtained with the polymer containing 20% SC12F (HS-4) in an OLED device with a turn on voltage of 11.8 V, a maximum luminance of 1202 cd/m(2)and a maximum luminous efficiency of 0.30 cd/A compared to other polymers with different feed ratio.
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    One-step preparation of binder-free nickel-containing graphene foam electrode for supercapacitors
    (Wiley, 2024) Gultekin, Sirin Siyahjani; Karimi, Aziz Ahmad; Can, Mustafa; Demic, Serafettin
    In this study, a nickel hydroxide (Ni(OH)2)-modified reduced graphene oxide (rGO) foam electrode for supercapacitor application is presented. The electrode was prepared without using a binder through a one-step process with three different ratios (NirGO1, NirGO2, and NirGo3). To compare the supercapacitor performance of the obtained graphene foam electrodes, rGO and rGO:carbon black (CB) standard electrodes with PVDF-HFP binder were also prepared. All electrodes were then characterized structurally (XPS, EDS, RAMAN, XRD, and FT-IR) and morphologically (SEM). Structural characterizations demonstrated that the Ni-containing electrodes were in alpha-Ni(OH)2:rGO structure. In addition, NirGO3 exhibited a specific capacitance of 800 F g-1 which is relatively the highest performance between the foam electrodes, while rGO:CB presented a specific capacitance of 900 F g-1. The results demonstrated that with the method proposed for electrode development, it was possible to obtain comparable results with the standard electrode rGO:CB. image