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    Electrochemical and optical properties of biphenyl bridged-dicarbazole oligomer films: Electropolymerization and electrochromism
    (Pergamon-Elsevier Science Ltd, 2009) Koyuncu, Sermet; Gültekin, Burak; Zafer, Ceylan; Bilgili, Hakan; Can, Mustafa; Demic, Şerafettin; 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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    Electroluminescence performance of a series of fluorene/2,5-di(2-thienyl)-1H-pyrrole polymers
    (Wiley, 2020) Bilgili, Hakan; Kara, Koray; Yenel, Esma; Demic, Şerafettin; Kuş, 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) Siyahjani Gültekin, Şirin; Karimi, Aziz Ahmad; Can, Mustafa; Demic, Şerafettin
    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 α-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.