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    Conventional and inverted organic light emitting diodes based on bright green emmisive polyfluorene derivatives
    (Elsevier Sci Ltd, 2018) Mucur, Selin Piravadili; Kok, Cansu; Bilgili, Hakan; Canimkurbey, Betul; Koyuncu, Sermet
    Electro-active green light-emitting polymers based on polyfluorene derivatives (SF5 and SF6) were synthesized by Suzuki coupling reaction. Effect of fluorenone moiety on the main chain of the polyfluorene with allyl subunit was investigated against to performance of both inverted bottom emission and conventional organic light emitting diodes (IBOLEDs and OLEDs, respectively). 2,2',2-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H- benzimidazole) (TPBI) was then utilized as an electron transport layer (ETL) to analyze the change in transport characteristics of the devices with a structure of ITO/PEDOT:PSS/polyfluorene/TPBI/Ca/Al. The results showed that efficiency enhanced nearly four times while the light output values were lowered with the insertion of TPBI as an ETL. In addition, IBOLEDs were also fabricated with a device architecture of ITO/ZnO/polyfluorene/V2O5 /Al being keen on backwards charge injection behavior of the polymers. IBOLEDs were fabricated by using synthesized zinc oxide (ZnO) as the electron-injecting layer. Luminance and luminous efficiency were significantly low while turn on voltages were too low with respect to the conventional devices fabricated. Further, annealing treatment were optimized for light output characteristics of the fabricated OLEDs. This study revealed the importance of charge transport feature of the synthesized polyfluorene derivatives in electroluminescent devices with variant architecture. (C) 2018 Elsevier Ltd. All rights reserved.
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    Effect of thiophene linker addition to fluorene-benzotriazole polymers with the purpose of achieving white emission in OLEDs
    (Royal Soc Chemistry, 2020) Kok, Cansu; Doyranli, Ceylan; Canimkurbey, Betul; Mucur, Selin Piravadili; Koyuncu, Sermet
    With the purpose of obtaining white emission from single layer organic light emitting diodes (OLEDs), fluorene benzotriazole based polymers with double bond subunits (namely TP2 and SP3 with and without thiophene linker, respectively) were synthesized by a Suzuki cross-coupling polymerization reaction. SP3 and TP2 were used as an emissive layer of the OLED devices due to their outstanding solubility in organic solvents, photoluminescence intensity and morphological suitability for fine thin film-forming capability. The optical, electrochemical, light emission and electroluminescence characteristics, Density Functional Theory (DFT) calculations and admittance spectroscopic analysis of OLEDs based on SP3 and TP2 were realized in detail to understand the effects of thiophene linker addition as a donor unit to the main chain of fluorene benzotriazole based polymers. As a result, TP2 emitted a bright yellow emission with a maximum brightness of 243 cd m(-2) at 40 mA cm(-2), and a maximum current efficiency of 1.38 cd A(-1) with more broad electroluminescence characteristics than SP3 polymer without the thiophene linker. SP3 emitted a greenish yellow emission with a maximum brightness of 1001 cd m(-2) at 845 mA cm(-2), and a maximum current efficiency of 0.33 cd A(-1). Carrier transport properties, charge carrier transit time and the equivalent circuit modelling studies were obtained through admittance spectroscopy. An equivalent circuit model with a combination of two resistors and one capacitor explained the charge conduction mechanism of SP3 and TP2 based OLEDs. SP3 and TP2 OLED devices represented typical p-type transporting characteristics with mobilities of 0.073 and 0.017 cm(2) V-1 s(-1), respectively with simplified device configuration. All the results indicate that thiophene addition to the main chain of fluorene benzotriazole based polymers with double bond subunits lead to a promising candidate for white emissive materials used in single layer white OLEDs.
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    New metallophthalocyanines including benzylphenoxy groups and investigation of their organic-field effect transistor (OFET) features
    (Elsevier Sci Ltd, 2022) Ozdemir, Mucahit; Altinisik, Sinem; Koksoy, Baybars; Canimkurbey, Betul; Koyuncu, Sermet; Durmus, Mahmut; Bulut, Mustafa
    In this study, metal and metal-free novel phthalocyanines containing peripheral and non-peripheral tetra 2-ben-zylphenoxy groups were synthesized. The compounds were characterized by UV-Vis, FT-IR, H-1 NMR, and MALDI-TOF mass spectrometry as well as elemental analysis. These new phthalocyanines exhibited excellent solubility in most organic solvents, and their redox behavior was investigated in different solvents such as dimethyl sulfoxide (DMSO) and dichloromethane (DCM). The redox behavior of the peripheral and non-peripheral phthalocyanine compounds 1a -c and 2a -c was determined by cyclic voltammetry and in situ spec-troelectrochemistry. According to organic field-effect transistors (OFETs) measurements, the peripheral and non-peripheral phthalocyanine-cobalt complexes which have higher mobility than others were utilized top-gate bottom-contact OFETs fabrication. The output characteristics of the device show that its mobility is approximately 5 x 10(-2) cm(2)/Vs with p-type accumulation.
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    Tuning the Electrochromic Properties of Fluorinated Benzochalcogenodiazole Based Donor-Acceptor Polymers
    (Wiley-V C H Verlag Gmbh, 2020) Colak, Betul; Altinisik, Sinem; Koyuncu, Fatma Baycan; Canimkurbey, Betul; Koyuncu, Sermet
    In this study, a series of benzochalcogenodiazole based donor acceptor monomers namely 4,7-bis(4-hexyl-2-thienyl)-2,1,3-benzothiadiazole (TST), 5,6-difluoro-4,7-bis(4-hexyl-2-thienyl)-2,1,3-benzothiadiazole (TST2) and 4,7-bis(4-hexyl-2-thienyl)-2,1,3-benzoselenadiazole (TSeT) were synthesized by Stille reaction and then directly polymerized on to Indium Tin Oxide coated glass (ITO/Glass) surface by electrochemical polymerization process. According to UV-Vis measurements, a 20 nm blue shift was detected at low energy band after fluorination of TST (TST2). Besides, a 40 nm red shift was observed by changing S to Se on the benzochalcogenodiazole moiety (TSeT). Thus, the optical band gaps were varied as 2.32, 2.45 and 2.16 eV for TST, TST2 and TSeT, respectively. According to AFM results, rougher surface was observed in the PTSeT thin film than that of PTST and PTST2. Thin films of electrodeposited polymers onto ITO/glass surface displayed ambipolar multi-electrochromic behavior both anodic and cathodic region. The ambipolar charge distribution was also observed in the theoretical DFT calculations. When the electrochromic performance of the polymer films was compared to each other, it was seen that the PTST2 has a better stability and higher the percentage transmittance change (Delta T%) at near-IR regime between neutral and oxidized states.