WoS İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/394
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Article Citation - WoS: 54Citation - Scopus: 57Ultralow Bandgap Molecular Semiconductors for Ambient-Stable and Solution-Processable Ambipolar Organic Field-Effect Transistors and Inverters(Royal Soc Chemistry, 2017) Ozdemir, Resul; Choi, Donghee; Ozdemir, Mehmet; Kwon, Guhyun; Kim, Hyekyoung; Sen, Unal; Usta, HakanThe design and development of novel ambipolar semiconductors is very crucial to advance various optoelectronic technologies including organic complementary (CMOS) integrated circuits. Although numerous high-performance ambipolar polymers have been realized to date, small molecules have been unable to provide high ambipolar performance in combination with ambient-stability and solution-processibility. In this study, by implementing highly p-electron deficient, ladder-type IFDK/IFDM acceptor cores with bithiophene donor units in D-A-D pi-architectures, two novel small molecules, 2OD-TTIFDK and 2OD-TTIFDM, were designed, synthesized and characterized in order to achieve ultralow band-gap (1.21-1.65 eV) semiconductors with sufficiently balanced molecular energetics for ambipolarity. The HOMO/LUMO energies of the new semiconductors are found to be -5.47/-3.61 and -5.49/-4.23 eV, respectively. Bottom-gate/top-contact OFETs fabricated via solution-shearing of 2OD-TTIFDM yield perfectly ambient stable ambipolar devices with reasonably balanced electron and hole mobilities of 0.13 cm(2) V-1 s(-1) and 0.01 cm(2) V-1 s(-1), respectively with I-on/I-off ratios of similar to 10(3)-10(4), and 2OD-TTIFDK-based OFETs exhibit ambipolarity under vacuum with highly balanced (mu(e)/mu(h) similar to 2) electron and hole mobilities of 0.02 cm(2) V-1 s(-1) and 0.01 cm(2) V-1 s(-1), respectively with I-on/I-off ratios of similar to 10(5)-10(6). Furthermore, complementary-like inverter circuits were demonstrated with the current ambipolar semiconductors resulting in high voltage gains of up to 80. Our findings clearly indicate that ambient-stability of ambipolar semiconductors is a function of molecular orbital energetics without being directly related to a bulk p-backbone structure. To the best of our knowledge, considering the processing, charge-transport and inverter characteristics, the current semiconductors stand out among the best performing ambipolar small molecules in the OFET and CMOS-like circuit literature. Our results provide an efficient approach in designing ultralow band-gap ambipolar small molecules with good solution-processibility and ambient-stability for various optoelectronic technologies, including CMOS-like integrated circuits.Article Citation - WoS: 12Citation - Scopus: 11Trans-Cis Isomerization Assisted Synthesis of Solution-Processable Yellow Fluorescent Maleic Anhydrides for White-Light Generation(Elsevier Science SA, 2015-12) Ozdemir, Mehmet; Genc, Sinan; Ozdemir, Resul; Altintas, Yemliha; Citir, Murat; Sen, Unal; Usta, HakanHeterocyclic maleic anhydride derivatives have been extensively studied in natural products chemistry over the past few decades. However, their incorporation into optoelectronic devices has lagged behind that of other pi-conjugated systems, and they have never been studied in white light emitting diodes (WLEDs). The development of emissive pi-conjugated materials for (WLEDs) has been an emerging scientific and technological research area to replace phosphors used in LED-based solid-state lighting. Here, we demonstrate the design, synthesis and characterization of two new highly emissive alkyl-substituted bis(thienyl)maleic anhydrides (C6-Th2MA and C12-Th2MA) with favorable photophysical properties. The new core is synthesized via a novel trans-to-cis isomerization-assisted one-pot reaction, which is demonstrated for the first time in the literature for the synthesis of a bis(heteroaryl)maleic anhydride. Due to its favorable absorption and fluorescence properties in the blue and yellow region of the visible spectrum, respectively, C12-Th2MA is studied as a potential wavelength-upconverting material. A WLED fabricated by drop-casting a polymeric solution of C12-Th2MA on a blue LED (InGaN, 455 nm) yields promising CIE coordinates and color-rendering index (CRI) values of (0.24, 0.20) and 65.0, respectively. Considering the simplicity of the current molecular structure and facile synthesis, alkyl-substituted bis(thienyl)maleic anhydrides stand as ideal phosphor alternatives. Therefore, the current findings may open new perspectives for the development of maleic anhydride-based small molecules for low-cost, energy-efficient, and solution-processed lighting technologies. (C) 2015 Elsevier B.V. All rights reserved.Article Citation - WoS: 28Citation - Scopus: 29Three-Dimensional Au-Coated Electrosprayed Nanostructured BODIPY Films on Aluminum Foil as Surface-Enhanced Raman Scattering Platforms and Their Catalytic Applications(Amer Chemical Soc, 2017-05-16) Yilmaz, Mehmet; Erkartal, Mustafa; Ozdemir, Mehmet; Sen, Unal; Usta, Hakan; Demirel, GokhanThe design and development of three-dimensional (3D) nanostructures with high surface-enhanced Raman scattering (SERS) performances have attracted considerable attention in the fields of chemistry, biology, and materials science. Nevertheless, electrospraying of organic smalt molecules on low-cost flexible substrates has never been studied to realize large-scale SERS-active platforms. Here, we report the facile, efficient, and low-cost fabrication of-Stable and reproducible Au-coated electrosprayed organic semiconductor films (Au@BDY-4TEBDY) on flexible regular aluminum foil at a large scale (5 cm X 5 cm) for practical SERS and catalytic applications. To this end, a well-designed-acceptor-donor-atceptor-type solution-processable molecular semiconductor, BDY-4T-BDY, developed by our group, is used because of its advantageous structural and electrical properties. The morphology of the electrosprayed organic film changes by solution concentration, and two different 3D morphologies with out-of-plane features are obtained. Highly uniform dendritic nanoribbons with sharp needle-like tips and vertically oriented nanoplates (similar to 50 nm thickness) are achieved when electrospraying solution concentrations of 240 and 253% w/v.(mgimL) are, respectively, used. When these electrosprayed organic films are coated with a nanoscopic thin (30 nm) Au layer, the resulting Au@BDY-4T-BDY platforms demonstrate remarkable SERS enhancement factors up to 1.7 X 10(6) with excellent Raman signal reproducibility (relative standard deviation <= 0.13) for methylene blue over the entire film. Finally, Au@BDY-4T-BDY films showed good catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol with rate constants of 1.3 X 10(-2) and 9.2 X 10(-3) min(-1). Our results suggest that electrospraying of rationally designed organic semiconductor molecules on flexible substrates holds great promise to enable low-cost, solution-processed, SERS-active platforms.Conference Object Thin Films of Inert Metal Nanowires for Display Applications(Tanger Ltd, 2015) Citir, Murat; Sen, Unal; Usta, Hakan; Canlier, Ali; Hakan, Usta; Ali, Canlier; Murat, Citir; Unal, SenAg nanowire transparent electrode has excellent transmittance (90%) and sheet resistance (20 Ohm/sq), yet there are slight drawbacks such as optical haze and chemical instability against aerial oxidation. Chemical stability of Ag nanowires needs to be improved in order for it to be suitable for electrode applications. Coating Ag nanowires with a thin layer of inert metals such as Au and Pd through galvanic exchange reactions may enhance the chemical stability of Ag nanowire films highly and also helps to obtain lower haze. In this study, coating of thin Au and Pd layers has been applied successfully onto the surface of Ag nanowires. Usually coatings are carried out by salts such as HAuCl4 and K2PdCl4 in order to make nanotubes. In this study, novel ethylenediamine(en) complexes of inert metal cations with mild oxidation power were prepared in order to oxidize Ag atoms partially on the surface through galvanic displacement. The mild galvanic exchange allowed for a thin layer (1-4 nm) of inert metal coating on the Ag nanowires with minimal truncation of the nanowire, where the average lengths and the diameters were between 10 similar to 14 mu m and 55 similar to 65 nm, respectively. The crystalline structure of the shell was formed epitaxially on the surface. The new Ag nanowires were suspended in methanol and then electrostatically sprayed on glass and flexible substrates. It was revealed that average total transmittance remain around 90% within visible spectrum region (400-800 nm) whereas sheet resistance rises up to 175 Ohm/sq. Very thin layer of inert metal costs low, though this may render an excellent catalyst for applications such as fuel cell and organic synthesis, whereas transparent films of inert metal-coated Ag nanowire can be utilized as working electrodes for spectro-electrochemical cells as well.Article Citation - WoS: 8Citation - Scopus: 9Synthesis of Benzotriazole Functionalized ZIF-8 by Postsynthetic Modification for Enhanced CH4 and CO2 Uptakes(Elsevier, 2022-08) Erkartal, Mustafa; Incekara, Kaan; Sen, UnalIn this work, a series of functionalized ZIF-8 were synthesized via incorporation of benzotriazole ligands into the framework with a post-synthetic method. The crystal structure and porosity were preserved for all functionalized samples. Although a relatively low percentage of ligand exchange (approximately 10-22%) was observed due to steric and kinetic effects, a remarkable improvement was found in CO2 and CH4 uptake capacities due to the incorporation of more polar N sites into the structure and the change in pore size of the frameworks. The resulting ZIF-8-S5 exhibited 45.17(CO2) and 15.08 (CH4) cm(3) g(-1) at 273 K under 1.2 bar, which corresponds to an enhancement of 20 and 35% compared to pristine ZIF-8. Further, all functionalized samples showed the significant improvement of selective CO2 over N-2.Article Citation - WoS: 24Citation - Scopus: 24Proton-Conducting Blend Membranes of Nafion/Poly(Vinylphosphonic Acid) for Proton Exchange Membrane Fuel Cells(Springer, 2013-08-08) Sen, Unal; Acar, Oktay; Celik, Sevim Unugur; Bozkurt, Ayhan; Ata, Ali; Tokumasu, Takashi; Miyamoto, AkiraNafion/poly(vinylphosphonic acid) blends were synthesized and characterized in this work. Poly(vinylphosphonic acid), PVPA, was synthesized by the free-radical polymerization of vinylphosphonic acid. Then Nafion/PVPA blend membranes were prepared by means of film casting from Nafion/PVPA solutions with several molar ratios of PVPA repeat unit to - SO3H. Homogeneous Nafion/PVPA films were produced. Nafion-PVPA interactions were studied by Fourier transform infrared (FT-IR) spectroscopy. Thermal properties were investigated via thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The TGA results illustrated that all of these Nafion/PVPA electrolytes are thermally stable up to 400 degrees C. The membrane properties were further characterized by studying their morphologies using scanning electron microscopy (SEM). The proton conductivity of the Nafion/P(VPA)(3) blend membrane was 1.1x10(-5) S/cm in an anhydrous state at 130 degrees C. The conductivities of the blends increased by at least three orders of magnitude upon hydration, exceeding 10(-2) S/cm with RH=50 % at ambient temperature.Article Citation - WoS: 104Citation - Scopus: 109Proton Conducting Poly(Vinyl Alcohol) (PVA)/Poly (2-Acrylamido Sulfonic Acid) (PAMPS)/Zeolitic Imidazolate Framework (ZIF) Ternary Composite Membrane(Elsevier, 2016-02) Erkartal, Mustafa; Usta, Hakan; Citir, Murat; Sen, UnalThe design, synthesis and characterization of novel proton exchange membranes (PEMs) are of significant scientific and technological importance for the realization of fuel cells, actuators, and sensors. Here, we demonstrate a novel ternary composite membrane consisting of poly(vinyl alcohol) (PVA), poly (2-acrylamido-2-methylpropane sulfonic acid) (PAMPS), zeolitic imidazolate framework-8 (ZIF-8), which is prepared by physical blending and casting methods. To enhance the water management of the membranes, in situ chemical cross-linking is carried out by glutaraldehyde (GA). During the characterization of the new membranes, FT-IR is used for intermolecular and inter-polymer interactions between different components of the membrane, SEM is used to identify morphology, XRD is used to prove the presence of ZIF-8 nanoparticles, and finally TGA is used for thermal stability. The proton conductivity of the membranes is found to increase with temperature and also with the increasing content of PAMPS. The highest proton conductivity under fully hydrated state at 80 degrees C is measured as 0.134 S cm(-1) for PVA: PAMPS: ZIF-8 (55:40:5) composition. In this study, it is clearly shown that ZIF-8 nanoparticles contribute to the proton conductivity by forming hydrogen bonds with the polymer network in the membrane. The water uptake (WU) and ion exchange capacity (IEC) values are 3.28 (gig) and 1.52 meq g(-1), respectively for the same membrane. To the best our knowledge, this study shows one of the first example of a MOFcontaining membrane with truly high proton conductivities, and both values of proton conductivity and electrochemical properties are comparable to those of well-studied membrane, Nation. (C) 2015 Elsevier B.V. All rights reserved.Article Citation - WoS: 54Citation - Scopus: 58Proton Conducting Self-Assembled Metal-Organic Framework/Polyelectrolyte Hollow Hybrid Nanostructures(Amer Chemical Soc, 2016-08-29) Sen, Unal; Erkartal, Mustafa; Kung, Chung-Wei; Ramani, Vijay; Hupp, Joseph T.; Farha, Omar K.Herein, a room temperature chemical process to synthesize functional, hollow nanostructures from zeolitic imidazolate framework-8 (ZIF-8) and poly(vinylphosphonic acid) (PVPA) is reported. Syntheses are initiated by physically blending the components a process that is accompanied first by encapsulation of ZIF-8 crystallites by PVPA and then by fragmentation of the crystallites. The fragmentation process is driven by partial displacement of the methyl-imidazolate ligands of Zn(II) in ZIF-8 by phosphonate groups on PVPA. Differences in rates of diffusion for the components of the reactive mixture yield a Kirkendall-like effect that is expressed as a hollow-particle morphology. The obtained hollow nanostructures feature hybrid shells containing PVPA, ZIF-8, and their cross-reacted products. The hybrid structures display substantial proton conductivities that increase with increasing temperature, even under the anhydrous conditions prevailing at temperatures above the boiling point of water. For example, at T = 413 K the proton conductivity of ZIF-8@PVPA reaches 3.2 (+/- 0.12) x 10(-3) S cm(-1), a value comparatively higher than that for PVPA (or ZIF-8) in isolation. The high value may reflect the availability in the hybrid structures of free (and partially free), amphoteric imidazole species, and their hydrogen-bonding interactions with phosphonate and/or phosphonic acid units. The persistence of ample conductivity at high temperature reflects the elimination of phosphonic acid group dehydration and dimerization-an effect that strikingly degrades the conductivity of pure PVPA under anhydrous conditions.Article Citation - WoS: 18Citation - Scopus: 21Poly(Lauryl Methacrylate)-Grafted Amino-Functionalized Zirconium-Terephthalate Metal-Organic Framework: Efficient Adsorbent for Extraction of Polycyclic Aromatic Hydrocarbons from Water Samples(Amer Chemical Soc, 2020-05-20) Tabatabaii, Maryam; Khajeh, Mostafa; Oveisi, Ali Reza; Erkartal, Mustafa; Sen, UnalIn this study, a novel porous hybrid material, poly(lauryl methacrylate) polymer-grafted UiO-66-NH2 (UiO = University of Oslo), was synthesized for efficient extraction of polycyclic aromatic hydrocarbons (PAHs) from aqueous samples. The polymer end-tethered covalently to the MOF's surface was synthesized by surface-initiated atom transfer radical polymerization, revealing a distinct type of morphology. The adsorbent was characterized by scanning electron microscopy, energy-dispersive spectroscopy, transmission electron microscopy, powder X-ray diffraction, N-2 adsorption-desorption analysis, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The analyses were carried out by gas chromatography-mass spectrometry. Parameters including the type and volume of the eluent, the amount of the adsorbent, and adsorption and desorption times were investigated and optimized. Under optimal conditions, the limit of detection, intraday precision, and interday precision were in the range of 3-8 ng L-1, 1.4-3.1, and 4.1-6.5%, respectively. The procedure was used for analysis of PAHs from natural water samples.Article Citation - WoS: 68Citation - Scopus: 68Micro-/Nanostructured Highly Crystalline Organic Semiconductor Films for Surface-Enhanced Raman Spectroscopy Applications(Wiley-VCH Verlag GmbH, 2015-08-11) Yilmaz, Mehmet; Ozdemir, Mehmet; Erdogan, Hakan; Tamer, Ugur; Sen, Unal; Facchetti, Antonio; Demirel, GokhanThe utilization of inorganic semiconductors for surface-enhanced Raman spectroscopy (SERS) has attracted enormous interest. However, despite the technological relevance of organic semiconductors for enabling inexpensive, large-area, and flexible devices via solution processing techniques, these p-conjugated systems have never been investigated for SERS applications. Here for the first time, a simple and versatile approach is demonstrated for the fabrication of novel SERS platforms based on micro-/nanostructured 2,7-dioctyl[1]benzothieno[3,2-b][1] benzothiophene (C8-BTBT) thin films via an oblique-angle vapor deposition. The morphology of C8-BTBT thin films is manipulated by varying the deposition angle, thus achieving highly favorable 3D vertically aligned ribbon-like micro-/nanostructures for a 90 degrees deposition angle. By combining C8-BTBT semiconductor films with a nanoscopic thin Au layer, remarkable SERS responses are achieved in terms of enhancement (approximate to 10(8)), stability (>90 d), and reproducibility (RSD < 0.14), indicating the great promise of Au/C8-BTBT films as SERS platforms. Our results demonstrate the first example of an organic semiconductor-based SERS platform with excellent detection characteristics, indicating that p-conjugated organic semiconductors have a great potential for SERS applications.