WoS İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/394
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Article Citation - WoS: 13Citation - Scopus: 11Understanding the Effect of Symmetry Breaking on Plasmon Coupling From TDDFT(Amer Chemical Soc, 2021-05-26) Alkan, Fahri; Aikens, Christine M.We perform a time-dependent density functional theory (TDDFT) investigation for the optical properties of nanorod assemblies for different sizes (Ag-10, Ag-59, and Ag-139), interparticle distances, and orientations with a focus on the effect of symmetry breaking via an angle on plasmon coupling. For the model systems, the angle (theta) between the particles is varied between 0 and 180 degrees, where theta = 0 degrees and theta = 180 degrees correspond to symmetric side-by-side and end-to-end orientations of the nanorods, respectively. Our analysis reveals that for a sufficiently large interparticle distance (r > 0.7 nm), where the wave-function overlap between monomers is negligible, TDDFT results agree quite well with the predictions of the dipole-dipole interaction model for the intensity of the different modes of coupled plasmons. For smaller gap distances (0.4-0.5 nm), a charge-transfer plasmon (CTP) mode occurs for the symmetry broken case of the Ag-10 dimer. For the assemblies of larger nanorods, however, the CTP mode is predicted to be less pronounced, especially for the cases where the deviation from the end-to-end geometry is larger than 30 degrees. The orbital overlap and configuration-interaction analyses show that these results are related to the fact that the relative overlap strength between monomeric energy levels is significantly reduced for symmetry-broken orientations of larger nanorods.Article Citation - WoS: 19Citation - Scopus: 19Understanding and Tailoring Excited State Properties in Solution-Processable Oligo(p-Phenyleneethynylene)s: Highly Fluorescent Hybridized Local and Charge Transfer Character via Experiment and Theory(Amer Chemical Soc, 2021-10-13) Usta, Hakan; Cosut, Bunyemin; Alkan, FahriRod-shaped oligo(p-phenyleneethynylene) (OPE) offers an attractive p-framework for the development of solution-processable highly fluorescent molecules having tunable hybridized local and charge transfer (HLCT) excited states and (reverse) intersystem crossing ((R)ISC) channels. Herein, an HLCT oligo(p-phenyleneethynylene) library was studied for the first time in the literature in detail systematically via experiment and theory. The design, synthesis, and full characterization of a new highly fluorescent (Phi(PL-solution) similar to 1) sky blue emissive 4',4 ''-((2,5-bis((2-ethylhexyl)oxy)-1,4-phenylene)bis(ethyne-2,1-diyl))bis(N,N-diphenyl-[1,1'-bi-phenyl]-4-amine) (2EHO-TPA-PE) was also reported. The new molecule consists of a D'-Ar-pi-D-pi-Ar-D' molecular architecture with an extended pi-spacer and no acceptor unit, and detailed structural, physicochemical, single-crystal, and optoelectronic characterizations were performed. A high solid-state quantum efficiency (Phi(PL-solution) similar to 0.8) was achieved as a result of suppressed exciton-phonon/vibronic couplings (no pi-pi interactions and multiple (14 per dimeric form) strong C-H center dot center dot center dot pi interactions). Strong solution-phase/solid-state dipole-dependent tunable excited state behavior (local excited (LE) -> HLCT -> charge transfer (CT)) and decay dynamics covering a wide spectral region were demonstrated, and the CT state was observed to be highly fluorescent despite extremely large Stokes shift (similar to 130 nm)/fwhm (similar to 125 nm) and significant charge separation (0.75 charge.nm). Employing the Lippert-Mataga model, along with detailed photophysical studies and TDDFT calculations, key relationships between molecular design-electronic structure-exciton characteristics were elucidated with regards to HLCT and hot exciton channel formations. The interstate coupling between CT and LE states and the interplay of this coupling with respect to medium polarity were explored. A key relationship between excited-state symmetry breaking process and the formation of HLCT state was discussed for TPA-ended rod-shaped OPE p-systems. (R)ISC-related delayed fluorescence (tau similar to 2-6 ns) processes were evident following the prompt decays (similar to 0.4-0.9 ns) both in the solution and in the solid-state. As a unique observation, the delayed fluorescence could be tuned and facilitated via small dielectric changes in the medium. Our results and the molecular engineering perspectives presented in this study may provide unique insights into the structural and electronic factors governing tunable excited state and hot-exciton channel formations in OPEs for (un)conventional solution-processed luminescence applications.Article Citation - WoS: 4Citation - Scopus: 4Transparent Films Made of Highly Scattering Particles(Amer Chemical Soc, 2020-01-13) Erdem, Talha; Yang, Lan; Xu, Peicheng; Altintas, Yemliha; O'Neil, Thomas; Caciagli, Alessio; Eiser, ErikaToday, colloids are widely employed in various products from creams and coatings to electronics. The ability to control their chemical, optical, or electronic features by controlling their size and shape explains why these materials are so widely preferred. Nevertheless, altering some of these properties may also lead to some undesired side effects, one of which is an increase in optical scattering upon concentration. Here, we address this strong scattering issue in films made of binary colloidal suspensions. In particular, we focus on raspberry-type polymeric particles made of a spherical polystyrene core decorated by small hemispherical domains of acrylate with an overall positive charge, which display an unusual stability against aggregation in aqueous solutions. Their solid films display a brilliant red color due to Bragg scattering but appear completely white on account of strong scattering otherwise. To suppress the scattering and induce transparency, we prepared films by hybridizing them with oppositely charged PS particles with a size similar to that of the bumps on the raspberries. We report that the smaller PS particles prevent raspberry particle aggregation in solid films and suppress scattering by decreasing the spatial variation of the refractive index inside the film. We believe that the results presented here provide a simple strategy to suppress strong scattering of larger particles to be used in optical coatings.Article Citation - WoS: 13Citation - Scopus: 13Sulfobetaine-Based Homo- and Copolymers by Raft: Cross-Linked Micelles and Aqueous Solution Properties(Amer Chemical Soc, 2022-08-04) Gurdap, Seda; Bayram, Nazende Nur; Isoglu, Ismail Alper; Isoglu, Sevil Dincer; Dinçer İşoǧlu, SevilIn this study, we describe the synthesis and aqueous solution behavior of temperature-sensitive N-(3-sulfopropyl)-N-methacroyloxyethyl-N,N-dimethylammonium betaine (SBMA) homopolymers and core cross-linked micelles (CCMs) with an SBMA shell. Reversible addition- fragmentation chain transfer polymerization has been utilized to synthesize sulfobetaine homopolymers, followed by CCM formation during copoly-merization in the presence of an acid-degradable cross-linker. First, SBMA homopolymers of varying chain lengths were synthesized, and it has been demonstrated that an increase in the chain length and concentration of the homopolymer resulted in an increase in the upper critical solution temperature (UCST). Besides, micelles showed concentration-dependent dual temperature-sensitive behavior with UCST and LCST transitions. Also, homopolymers and CCMs were characterized by FTIR, H-1-NMR, GPC, and TEM. Micelle formation and temperature sensitivity were also investigated by DLS. As a result, stabilized micelles were successfully prepared with the motivation of preventing premature drug release and achieving a pH-and temperature-controlled system. Due to their dual-responsive characteristics, the CCMs show promising potential to be used as smart drug carriers for controlled delivery.Article Citation - WoS: 27Citation - Scopus: 29Revisiting the Role of Charge Transfer in the Emission Properties of Carborane-Fluorophore Systems: A TDDFT Investigation(Amer Chemical Soc, 2022-06-05) Tahaoglu, Duygu; Usta, Hakan; Alkan, FahriIn this study, we performed a detailed investigation of the S-1 potential energy surface (PES) of o-carborane-anthracene (o-CB-Ant) with respect to the C-C bond length on o-CB and the dihedral angle between o-CB and Ant moieties. The effects of different substituents (F, Cl, CN, and OH) on carbon- or boron-substituted o-CB, along with a pi-extended acene-based fluorophore, pentacene, on the nature and energetics of S-1 -> S-0 transitions are evaluated. Our results show the presence of a non-emissive S-1 state with an almost pure charge transfer (CT) character for all systems as a result of significant C-C bond elongation (C-C = 2.50-2.56 angstrom) on o-CB. In the case of unsubstituted o-CB-Ant, the adiabatic energy of this CT state corresponds to the global minimum on the S-1 PES, which suggests that the CT state could be involved in emission quenching. Despite large deformations on the o-CB geometry, predicted energy barriers are quite reasonable (0.3-0.4 eV), and the C-C bond elongation can even occur without a noticeable energy penalty for certain conformations. With substitution, it is shown that the dark CT state becomes even more energetically favorable when the substituent shows -M effects (e.g., -CN), whereas substituents showing +M effects (e.g., -OH) can result in an energy increase for the CT state, especially for partially stretched C-C bond lengths. It is also shown that the relative energy of the CT state on the PES depends strongly on the LUMO level of the fluorophore as this state is found to be energetically less favorable compared to other conformations when anthracene is replaced with pi-extended pentacene. To our knowledge, this study shows a unique example of a detailed theoretical analysis on the PES of the S-1 state in o-CB-fluorophore systems with respect to substituents or fluorophore energy levels. Our findings could guide future experimental work in emissive o-CB-fluorophore systems and their sensing/optoelectronic applications.Article Citation - WoS: 1Citation - Scopus: 1Osmotic-Pressure Nematic Ordering in Suspensions of Laponite and Carboxy Methyl Cellulose(Amer Chemical Soc, 2020-10-12) Xu, Peicheng; Yazici, Ahmet F.; Erdem, Talha; Lekkerkerker, Henk N. W.; Mutlugun, Evren; Eiser, ErikaLaponite is a synthetic clay that is known to form gels in aqueous suspensions at low concentrations (0.01 g/cm(3)) Although it is expected to form lyotropic liquid crystals, such phases usually do not form, as a consequence of laponite's tendency to form gels at concentrations below the threshold for liquid crystal formation. Here we show that macroscopic, birefringent phases of laponite can be prepared through osmotic compression of a laponite solution by an aqueous solution of carboxy methyl cellulose (CMC). We present polarization imaging studies showing how the initially dilute, isotropic laponite phase shrinks while developing typical birefringence colors between crossed polarizers. Using the MichelLevy interference charts, we were able to extract the refractive index and orientation of the laponite nanodisks in the compressed region. Our observations allow us to propose a tentative state diagram, indicating the concentration regions for which we obtain optically anisotropic gels.Article Citation - WoS: 12Citation - Scopus: 14Nanowire-Shaped MoS2@MoO3 Nanocomposites as a Hole Injection Layer for Quantum Dot Light-Emitting Diodes(Amer Chemical Soc, 2022-08-01) Bastami, Nasim; Soheyli, Ehsan; Arslan, Aysenur; Sahraei, Reza; Yazici, Ahmet Faruk; Mutlugun, EvrenMolybdenum disulfides and molybdenum trioxides are structures that possess the potential to work as efficient charge transport layers in optoelectronic devices. In the present study, as opposed to the existing Mo-based nanostructures in flake, sheet, or spherical forms, an extremely simple and low-cost hydrothermal method is used to prepare nanowires (NWs) of MoS2@MoO3 (MSO) composites. The synthesis method includes several advantages including easy handling and processing of inexpensive precursors to reach stable MSO NWs without the need for an oxygen-free medium, which would facilitate the possibility of mass production of these nanostructures. The structural analysis confirmed the formation of MSO nanocomposites with different Mo valence states, as well as NWs of average length and diameter of 70 nm and 5 nm, respectively. In order to demonstrate their potential for optoelectronic applications, MSO NWs were blended into hole injection layers (HILs) in quantum dot-based light emitting diodes (QLEDs). Electroluminescence measurements show a substantial enhancement in both luminance (from 44,330 to 68,630 cd.m-2) and external quantum efficiency (from 1.6 to 2.3%), based on the increase in the ratio of MSO NWs from 3 to 10%. Interestingly, the addition of 10% volume of MSO NWs resulted in a remarkably smoother HIL with improved current efficiency and stability in green-emitting QLEDs. The simplicity and cost-effective features of the synthesis method along with outstanding favorable morphology demonstrated their ability to enhance the QLED performance and mark them as promising agents for optoelectronics.Article Citation - WoS: 13Citation - Scopus: 15Meso-π-extended/Deficient BODIPYs and Low-Band Donor-Acceptor Copolymers for Organic Optoelectronics(Amer Chemical Soc, 2022-02-16) Can, Ayse; Choi, Gi-Seok; Ozdemir, Resul; Park, Soyoon; Park, Jin Su; Lee, Yongchul; Usta, HakanThe realization of pi-deficient acceptors and their donor-acceptor copolymers has become a key research focus for the realization of versatile organic optoelectronic materials and devices. Herein, we demonstrate the theoretical design, synthesis, and physicochemical/optoelectronic characterization of two meso-pi-extended/deficient BODIPY building blocks (2OD-T2BDY and 2OD-TTzBDY) and a library of donor-acceptor copolymers with low band gap (E-g = 1.30-1.35 eV) based on these building blocks. These building blocks, to the best of our knowledge, are the first examples of BODIPYs with meso-pi-extension. A library of BODIPY building blocks with varied meso units/substituents is studied to reveal the meso effects on the semiconducting BODIPY's optoelectronic properties. The building blocks showed favorable pi-acceptor electronic/structural properties with meso-pi-delocalized and stabilized LUMOs (ca. -3.6 eV) and large ground-state dipole moments of 4.9-5.5 D. Consistent with the theoretical/experimental pi-electronic structures, all copolymers functioned as p-type semiconductors in field-effect transistors and as donor materials in the bulk heterojunction organic photovoltaics. Power conversion efficiencies of up to 4.4% with a short-circuit current of 12.07 mA cm(-2) were achieved. This study demonstrates a unique meso-pi-extension strategy to realize BODIPYs with favorable pi-acceptor properties, and our findings could open up future materials design avenues in various organic optoelectronic applications.Article Citation - WoS: 2Citation - Scopus: 2Light-Controlled Electrostatic Self-Assembly of Quantum Dots(Amer Chemical Soc, 2025-04-11) Akrema; Phul, Ruby; Yazici, Ahmet Faruk; Senel, Zeynep; Erdem, TalhaElectrostatic self-assembly is one of the important self-assembly mechanisms that found use in optoelectronics. Although this method enables realizing unconventional architectures, producing complicated architectures in large areas requires local control over the self-assembly process. One of the ways to achieve this control is to provide enough kinetic energy to the self-assembling nanoparticles so that they can escape electrostatic attraction. We hypothesize that this energy can be delivered to the nanoparticles by treating them with light that can be absorbed by the particles. Here, we test this idea to tailor the electrostatic self-assembly of semiconductor quantum dots (QDs) using a laser. Employing fluorescence and atomic force microscopy, we demonstrate that the QDs are not attached to the substrate in regions where they are exposed to light while they are coated in the absence of optical excitation. We further conduct theoretical analysis to show that elevated temperatures indeed allow the QDs to escape the electrostatic attraction of the charged polymers on the surface. We also demonstrate that increasing the temperature during the coating process without irradiating the sample gives similar results as the case when the sample was irradiated. Finally, we fabricate an uncoated region on the self-assembled QD film with dimensions of similar to 200 mu m x 0.5 cm to demonstrate the feasibility of our approach to control the bottom-up self-assembly. We believe that our results may pave the way for a cost-effective and sustainable approach for the fabrication of nanoelectronic and optoelectronic devices.Article Citation - WoS: 5Citation - Scopus: 5Inkjet Printing of Aqueous Silver Inks on Water-Soluble Fabrics for Transient Electronics Applications(Amer Chemical Soc, 2024-07-29) Onses, Zehra Gozutok; Kiremitler, N. Burak; Ozbasaran, Aleyna; Huang, Xian; Onses, Mustafa Serdar; Usta, Hakan; Gozutok Onses, ZehraThere is an urgent need to develop practical routes for manufacturing transient electronic devices to tackle the emerging issue of electronic waste and enable next-generation devices. This study reports additive patterning of conductive layers on industrially available water-soluble nonwoven fabrics composed of poly(vinyl alcohol) (PVA). Aqueous inks composed of reactive silver precursors can be practically patterned over water-soluble fabrics by inkjet printing. The efficient deposition of materials with droplet volumes on the order of picoliters ensures the generation of conductive patterns on a water-soluble fabric using a solution-processable fabrication with aqueous inks. The fabrication of conductive electrodes and transience behavior are studied on PVA fabrics with two different degrees of hydrolysis, providing tunability in the temperature-dependent degradation of the substrate. The application of the printed conductive pads is demonstrated in resistive heaters. The temperature of the fabric can exceed 100 degrees C in less than 15 s at a safe voltage of 3 V. The heater exhibits stable operation under cyclic heating and cooling. The presented approach presents key opportunities in additive patterning of aqueous solutions and colloidal dispersions over water-soluble substrates for transient device applications.