WoS İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/394
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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: 18Citation - Scopus: 18Ultrahigh Vacuum Self-Assembly of Rotationally Commensurate C8-BTBT/MoS2 Mixed-Dimensional Heterostructures(Amer Chemical Soc, 2019-02-12) Liu, Xiaolong; Balla, Itamar; Sangwan, Vinod K.; Usta, Hakan; Facchetti, Antonio; Marks, Tobin J.; Hersam, Mark C.Mixed-dimensional van der Waals heterostructures combine the advantages of nanomaterials with qualitatively distinct properties such as the extended bandstructures and high charge carrier mobilities of inorganic two-dimensional materials and the discrete orbital energy levels and strong optical absorption of zero-dimensional organic molecules. The synergistic interplay between nanomaterials of distinct dimensionality has enabled a variety of unique applications such as antiambipolar transistors, sensitized photodetectors, and gate-tunable photovoltaics. Because the performance of mixed-dimensional heterostructure devices depends sensitively on the buried interfacial structure, it is of great interest to identify materials and chemistries that naturally form highly ordered heterointerfaces. Toward this end, here we demonstrate ultrahigh vacuum self-assembly of 2,7-dioctyl[1]benzothieno [3,2-b][1]benzothiophene (C8-BTBT) monolayers onto epitaxial MoS2/graphene heterostructures. With molecular-resolution scanning tunneling microscopy and spectroscopy, the resulting C8-BTBT/MoS2/graphene mixed-dimensional heterostructures are found to be rotationally commensurate with well-defined physical and electronic structures. It is further shown that the self-assembled C8-BTBT monolayers are insensitive to the structural defects and electronic perturbations of the underlying MoS2 substrate, which provides significant processing latitude. For these reasons, this work will facilitate ongoing efforts to utilize organic/MoS2/graphene mixed-dimensional heterostructures for electronic, optoelectronic, and photovoltaic applications.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.Article Citation - WoS: 61Citation - Scopus: 74Solution-Processable Bodipy-Based Small Molecules for Semiconducting Microfibers in Organic Thin-Film Transistors(Amer Chemical Soc, 2016-05-23) Ozdemir, Mehmet; Choi, Donghee; Kwon, Guhyun; Zorlu, Yunus; Cosut, Bunyemin; Kim, Hyekyoung; Usta, HakanElectron-deficient pi-conjugated small molecules can function as electron-transporting semiconductors in various optoelectronic applications. Despite their unique structural, optical, and electronic properties, the development of BODIPY-based organic semiconductors has lagged behind that of other pi-deficient units. Here, we report the design and synthesis of two novel solution-proccessable BODIPY-based small molecules (BDY-3T-BDY and BDY-4T-BDY) for organic thin-film transistors (OTFTs). The new semiconductors were fully characterized by H-1/C-13 NMR, mass spectrometry, cyclic voltammetry, UV-vis spectroscopy, photoluminescence, differential scanning calorimetry, and thermogravimetric analysis. The single-crystal X-ray diffraction (XRD) characterization of a key intermediate reveals crucial structural properties. Solution-sheared top-contact/bottom-gate OTFTs exhibited electron mobilities up to 0.01 cm(2)/V center dot s and current on/off ratios of >10(8). Film microstructural and morphological characterizations indicate the formation of relatively long (similar to 0.1 mm) and micrometer-sized (1-2 mu m) crystalline fibers for BDY-4T-BDY-based films along the shearing direction. Fiber-alignment-induced charge-transport anisotropy (mu?/mu approximate to 10) was observed, and higher mobilities were achieved when the microfibers were aligned along the conduction channel, which allows for efficient long-range charge-transport between source and drain electrodes. These OTFT performances are the highest reported to date for a BODIPY-based molecular semiconductor, and demonstrate that BODIPY is a promising building block for enabling solution-processed, electron-transporting semiconductor films.Article Citation - WoS: 11Citation - Scopus: 13Solution-Processable Indenofluorenes on Polymer Brush Interlayer: Remarkable N-Channel Field-Effect Transistor Characteristics Under Ambient Conditions(Amer Chemical Soc, 2023-08-15) Can, Ayse; Deneme, Ibrahim; Demirel, Gokhan; Usta, HakanThe development of solution-processable n-type molecularsemiconductorsthat exhibit high electron mobility (& mu;(e) & GE;0.5 cm(2)/(V & BULL;s)) under ambient conditions, along withhigh current modulation (I (on)/I (off) & GE; 10(6)-10(7)) andnear-zero turn on voltage (V (on)) characteristics,has lagged behind that of other semiconductors in organic field-effecttransistors (OFETs). Here, we report the design, synthesis, physicochemicaland optoelectronic characterizations, and OFET performances of a libraryof solution-processable, low-LUMO (-4.20 eV) 2,2 & PRIME;-(2,8-bis(3-alkylthiophen-2-yl)indeno[1,2-b]fluorene-6,12-diylidene)dimalononitrile small molecules, & beta;,& beta;& PRIME;-C (n) -TIFDMTs, having varied alkyl chain lengths (n = 8, 12, 16). An intriguing correlation is identifiedbetween the solid-isotropic liquid transition enthalpies andthe solubilities, indicating that cohesive energetics, which are tunedby alkyl chains, play a pivotal role in determining solubility. Thesemiconductors were spin-coated under ambient conditions on denselypacked (grafting densities of 0.19-0.45 chains/nm(2)) ultrathin (& SIM;3.6-6.6 nm) polystyrene-brush surfaces.It is demonstrated that, on this polymer interlayer, thermally induceddispersive interactions occurring over a large number of methyleneunits between flexible alkyl chains (i.e., zipper effect) are criticalto achieve a favorable thin-film crystallization with a proper microstructureand morphology for efficient charge transport. While C-8 and C-16 chains show a minimal zipper effect upon thermalannealing, C-12 chains undergo an extended interdigitationinvolving & SIM;6 methylene units. This results in the formationof large crystallites having lamellar stacking ((100) coherence length & SIM;30 nm) in the out-of-plane direction and highly favorablein-plane & pi;-interactions in a slipped-stacked arrangement. Uninterruptedmicrostructural integrity (i.e., no face-on (010)-oriented crystallites)was found to be critical to achieving high mobilities. The excellentcrystallinity of the C-12-substituted semiconductor thinfilm was also evident in the observed crystal lattice vibrations (phonons)at 58 cm(-1) in low-frequency Raman scattering. Two-dimensionalmicrometer-sized (& SIM;1-3 & mu;m), sharp-edged plate-likegrains lying parallel with the substrate plane were observed. OFETsfabricated by the current small molecules showed excellent n-channelbehavior in ambient with & mu;(e) values reaching & SIM;0.9cm(2)/(V & BULL;s), I (on)/I (off) & SIM; 10(7)-10(8), and V (on) & AP; 0 V. Our study notonly demonstrates one of the highest performing n-channel OFET devicesreported under ambient conditions via solution processing but alsoelucidates significant relationships among chemical structures, molecularproperties, self-assembly from solution into a thin film, and semiconductingthin-film properties. The design rationales presented herein may openup new avenues for the development of high-electron-mobility novelelectron-deficient indenofluorene and short-axis substituted donor-acceptor & pi;-architectures via alkyl chain engineering and interface engineering.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.Conference Object Polymeric Semiconductors Based on Meso-Substituted BODIPY for (Opto)electronic Applications(Amer Chemical Soc, 2019) Usta, Hakan; Kim, Choongik; Kim, BumjoonConference Object Photophysical Properties of Self-Assembled Supramolecular Peptide Nanofiber Organic Semiconductors(Amer Chemical Soc, 2015) Khalily, Mohammad Aref; Usta, Hakan; Guler, Mustafa O.Article Citation - WoS: 75Citation - Scopus: 74Perfluoroalkyl-Functionalized Thiazole Thiophene Oligomers as N-Channel Semiconductors in Organic Field-Effect and Light-Emitting Transistors(Amer Chemical Soc, 2014-11-04) Usta, Hakan; Sheets, William Christopher; Denti, Mitchell; Generali, Gianluca; Capelli, Raffaella; Lu, Shaofeng; Facchetti, AntonioDespite their favorable electronic and structural properties, the synthetic development and incorporation of thiazole-based building blocks into n-type semiconductors has lagged behind that of other pi-deficient building blocks. Since thiazole insertion into pi-conjugated systems is synthetically more demanding, continuous research efforts are essential to underscore their properties in electron-transporting devices. Here, we report the design, synthesis, and characterization of a new series of thiazolethiophene tetra- (1 and 2) and hexa-heteroaryl (3 and 4) co-oligomers, varied by core extension and regiochemistry, which are end-functionalized with electron-withdrawing perfluorohexyl substituents. These new semiconductors are found to exhibit excellent n-channel OFET transport with electron mobilities (mu(e)) as high as 1.30 cm(2)/(V center dot s) (I-on/I-off > 10(6)) for films of 2 deposited at room temperature. In contrary to previous studies, we show here that 2,2'-bithiazole can be a very practical building block for high-performance n-channel semiconductors. Additionally, upon 2,2'- and 5,5'-bithiazole insertion into a sexithiophene backbone of well-known DFH-6T, significant charge transport improvements (from 0.0010.021 cm(2)/(V center dot s) to 0.200.70 cm(2)/(V center dot s)) were observed for 3 and 4. Analysis of the thin-film morphological and microstructural characteristics, in combination with the physicochemical properties, explains the observed high mobilities for the present semiconductors. Finally, we demonstrate for the first time implementation of a thiazole semiconductor (2) into a trilayer light-emitting transistor (OLET) enabling green light emission. Our results show that thiazole is a promising building block for efficient electron transport in ?-conjugated semiconductor thin-films, and it should be studied more in future optoelectronic applications.Conference Object Organic Semiconductor Based Surface-Enhanced Raman Spectroscopy Platforms(Amer Chemical Soc, 2018) Demirel, Gokhan; Usta, Hakan; Facchetti, Antonio