Scopus İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/395
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Doctoral Thesis FUNCTIONALIZED LOW LUMO [1]BENZOTHIENO[3,2-B][1]BENZOTHIOPHENE (BTBT)-BASED MOLECULAR SEMICONDUCTORS FOR ORGANIC FIELD EFFECT TRANSISTORS(Abdullah Gül Üniversitesi, Fen Bilimleri Enstitüsü, 2021) Özdemir, Resul; Usta, HakanDAcTTs have provided an excellent π-framework for the development of high mobility p-type molecular semiconductors in the past decade. However, n-type DAcTTs are rare and their electron transporting characteristics remain largely unexplored. In the second chapter of this thesis, the first example of an n-type BTBT-based semiconductor, D(PhFCO)-BTBT, has been realized via a two-step transition metal-free process without using chromatographic purification. The corresponding TC/BG-OFET devices demonstrated μe (max) = ~0.6 cm2/Vs and Ion/Ioff ratio = 107-108. The large band-gap BTBT π-core is a promising candidate for high mobility n-type organic semiconductors and, combination of very large intrinsic charge transport capabilities and optical transparency, may open a new perspective for next-generation (opto)electronics. In the third chapter of this thesis, a series of BTBT-based small molecules, D(C7CO)-BTBT, C7CO-BTBT-CC(CN)2C7, and D(C7CC(CN)2)-BTBT, have been developed in “S-F-BTBT-F-S (F/S: functional group/substituent)” molecular architecture. Combining with D(PhFCO)-BTBT, a molecular library with systematically varied chemical structures has been studied herein for the first time for low LUMO DAcTTs, and key relationships have been elucidated. The molecular engineering perspectives presented in this thesis may give unique insights into the design of novel electron transporting thienoacenes for unconventional optoelectronics.Article Citation - WoS: 16Citation - Scopus: 16The Hansen Solubility Approach Towards Green Solvent Processing: N-Channel Organic Field-Effect Transistors Under Ambient Conditions(Royal Soc Chemistry, 2024) Deneme, Ibrahim; Yildiz, Tevhide Ayca; Kayaci, Nilgun; Usta, HakanThe adoption of green solvents is of utmost importance for the solution-based fabrication of semiconductor thin films and for the commercialization of (opto)electronic devices, especially in response to evolving regulatory mandates for handling organic materials. Despite the increasing interest in this area, the scarcity of green solvent-processed n-channel OFETs, especially functioning under ambient conditions, highlights the need for further research. In this study, we demonstrated the Hansen solubility approach to study the solubility behavior of an ambient-stable n-type semiconductor, 2,2' -(2,8-bis(3-dodecylthiophen-2-yl)indeno[1,2-b]fluorene-6,12-diylidene)dimalononitrile (beta,beta'-C-12-TIFDMT), and to analyze potential green solvents for thin-film processing. The Hansen solubility parameters were determined to be delta(D) = 20.8 MPa1/2, delta(P) = 5.8 MPa1/2, and delta(H) = 5.5 MPa1/2 with a radius (R-0) of 8.3 MPa1/2. A green solvent screening analysis based on the minimal distance constraint and quantitative sustainability score identified ethoxybenzene, anisole, 2-methylanisole, and 2-methyltetrahydrofuran as suitable green solvents (R-a's = 5.17-7.93 MPa1/2 < R-0). A strong thermodynamic correlation was identified between the solubility and the semiconductor-solvent distance in the 3D Hansen solubility space, in which the maximum solubility limit could be estimated with the enthalpy of fusion (Delta H-fus) and melting temperature (T-mp) of the semiconductor. To the best of our knowledge, this relationship between the maximum solubility limit and thermal properties has been established for the first time for organic semiconductors. Bottom-gate/top-contact OFETs fabricated by spin-coating the semiconductor green solutions exhibited mu es reaching similar to 0.2 cm(2) V-1 s(-1) (I-on/I-off similar to 10(6)-10(7) and V-on similar to 0-5 V) under ambient conditions. This device performance, to our knowledge, is the highest reported for an ambient-stable green solvent-processed n-channel OFET. Our HSP-based rational approach and unique findings presented in this study can shed critical light on how green solvents can be efficiently incorporated in solution processing in organic (opto)electronics, and whether ambient-stable n-type semiconductors can continue to play an important role in green OFETs.Article Citation - WoS: 22Citation - Scopus: 24The Design and Fabrication of Supramolecular Semiconductor Nanowires Formed by Benzothienobenzothiophene (BTBT)-Conjugated Peptides(Royal Soc Chemistry, 2018) Khalily, Mohammad Aref; Usta, Hakan; Ozdemir, Mehmet; Bakan, Gokhan; Dikecoglu, F. Begum; Edwards-Gayle, Charlotte; Guler, Mustafa O.pi-Conjugated small molecules based on a [1]benzothieno[3,2-b]benzothiophene (BTBT) unit are of great research interest in the development of solution-processable semiconducting materials owing to their excellent charge-transport characteristics. However, the BTBT -core has yet to be demonstrated in the form of electro-active one-dimensional (1D) nanowires that are self-assembled in aqueous media for potential use in bioelectronics and tissue engineering. Here we report the design, synthesis, and self-assembly of benzothienobenzothiophene (BTBT)-peptide conjugates, the BTBT-peptide (BTBT-C-3-COHN-Ahx-VVAGKK-Am) and the C-8-BTBT-peptide (C-8-BTBT-C-3-COHN-Ahx-VVAGKK-Am), as -sheet forming amphiphilic molecules, which self-assemble into highly uniform nanofibers in water with diameters of 11-13(+/- 1) nm and micron-size lengths. Spectroscopic characterization studies demonstrate the J-type - interactions among the BTBT molecules within the hydrophobic core of the self-assembled nanofibers yielding an electrical conductivity as high as 6.0 x 10(-6) S cm(-1). The BTBT -core is demonstrated, for the first time, in the formation of self-assembled peptide 1D nanostructures in aqueous media for potential use in tissue engineering, bioelectronics and (opto)electronics. The conductivity achieved here is one of the highest reported to date in a non-doped state.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: 36Citation - Scopus: 36Selective Remanent Ambipolar Charge Transport in Polymeric Field-Effect Transistors for High-Performance Logic Circuits Fabricated in Ambient(Wiley-VCH Verlag GmbH, 2014-10-06) Fabiano, Simone; Usta, Hakan; Forchheimer, Robert; Crispin, Xavier; Facchetti, Antonio; Berggren, MagnusArticle 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: 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.Article Citation - WoS: 124Citation - Scopus: 127Molecular Engineering of Organic Semiconductors Enables Noble Metal-Comparable SERS Enhancement and Sensitivity(Nature Publishing Group, 2019-12-03) Demirel, Gokhan; Gieseking, Rebecca L. M.; Ozdemir, Resul; Kahmann, Simon; Loi, Maria A.; Schatz, George C.; Usta, HakanNanostructured molecular semiconductor films are promising Surface-Enhanced Raman Spectroscopy (SERS) platforms for both fundamental and technological research. Here, we report that a nanostructured film of the small molecule DFP-4T, consisting of a fully pi-conjugated diperfluorophenyl-substituted quaterthiophene structure, demonstrates a very large Raman enhancement factor (>10(5)) and a low limit of detection (10(-9) M) for the methylene blue probe molecule. This data is comparable to those reported for the best inorganic semiconductor- and even intrinsic plasmonic metal-based SERS platforms. Photoluminescence spectroscopy and computational analysis suggest that both charge-transfer energy and effective molecular interactions, leading to a small but non-zero oscillator strength in the charge-transfer state between the organic semiconductor film and the analyte molecule, are required to achieve large SERS enhancement factors and high molecular sensitivities in these systems. Our results provide not only a considerable experimental advancement in organic SERS figure-of-merits but also a guidance for the molecular design of more sensitive SERS systems.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: 10Citation - Scopus: 11Interplay Between Charge Injection, Electron Transport, and Quantum Efficiency in Ambipolar Trilayer Organic Light-Emitting Transistors(Wiley, 2022-01-15) Moschetto, Salvatore; Benvenuti, Emilia; Usta, Hakan; Ozdemir, Resul; Facchetti, Antonio; Muccini, Michele; Toffanin, StefanoThe fascinating characteristic of organic light-emitting transistors (OLETs) of being electrical switches with an intrinsic light-emitting capability makes them attractive candidates for a wide variety of applications, ranging from sensors to displays. To date, the OLET ambipolar trilayer heterostructure is the most developed architecture for maximizing device performance. However, a major challenge of trilayer OLETs remains the inverse correlation between external quantum efficiency and brightness under ambipolar conditions. The complex interconnection between electroluminescent and ambipolar charge transport properties, in conjunction with the limited availability of electron transport semiconducting materials, has indeed hampered the disruptive evolution of the OLET technology. Here, an in-depth study of the interplay of the key fundamental features that determine the device performance is reported by exploring electron transport semiconductors with different properties in ambipolar trilayer OLETs. Through the selection of compounds with tailored chemical structures, the relation between intrinsic optoelectronic characteristics of the electron transport semiconductor, energy level alignment within the structure, and morphological features is unraveled. Furthermore, the introduction of a suitable electron injector at the emissive/semiconducting layers interface sheds light into the bidimensional nature of OLETs that is a distinguishing factor of this class of devices with respect to prototypical organic light-emitting diodes.