Browsing by Author "Cosut, Bunyemin"

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A new rod-shaped BODIPY-acetylene molecule for solution-processed semiconducting microribbons in n-channel organic field-effect transistors
(ROYAL SOC CHEMISTRYTHOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND, 2017) Ozdemir, Mehmet; Choi, Donghee; Zorlu, Yunus; Cosut, Bunyemin; Kim, Hyungsug; Kim, Choongik; Usta, Hakan; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Usta, Hakan; Ozdemir, Mehmet
BODIPY-based pi-conjugated small molecules have been extensively studied in various fields of sensing and biochemical labelling; however, their use in organic optoelectronic applications is very limited. A new solution-processable acceptor-donor-acceptor (A-D-A) type small molecule, BDY-PhAc-BDY, consisting of BODIPY pi-acceptors and a rod-shaped 1,4-bis-(thienylethynyl) 2,5-dialkoxybenzene pi-donor, has been synthesized and fully characterized as a novel n-channel semiconductor in bottom-gate/top-contact organic field-effect transistors (OFETs). The new semiconductor exhibits an electrochemical band gap of 2.12 eV with highly stabilized HOMO/LUMO energy levels of -5.68 eV/-3.56 eV. Single-crystal X-ray diffraction (XRD) analysis of BDY-PhAc-BDY reveals a relatively low "BODIPY-meso-thiophene" dihedral angle (theta = 44.94 degrees), antiparallel pi-stacked BODIPY dimers with an interplanar distance of 3.93 angstrom, and strong "C-H center dot center dot center dot pi (2.85 angstrom)" interactions. The OFET devices fabricated by solution processing show the formation of highly-crystalline, one-dimensional (1-D) microribbons, which results in clear n-channel semiconductivity with an electron mobility of 0.004 cm(2) V-1 s(-1) and an on/off current ratio of 10(5)-10(6). To date, this is the highest reported for BODIPY-based small molecular semiconductors with alkyne linkages. Our results clearly demonstrate that BODIPY is an effective pi-acceptor unit for the design of solution-processable, electron-transporting organic semiconductors and easily fabricable 1-D semiconductor micro-/nano-structures for fundamental/applied research in organic optoelectronics.
Solution-Processable BODIPY-Based Small Molecules for Semiconducting Microfibers in Organic Thin-Film Transistors
(AMER CHEMICAL SOC1155 16TH ST, NW, WASHINGTON, DC 20036, 2016) Ozdemir, Mehmet; Choi, Donghee; Kwon, Guhyun; Zorlu, Yunus; Cosut, Bunyemin; Kim, Hyekyoung; Facchetti, Antonio; Kim, Choongik; Usta, Hakan; 0000-0002-0618-1979; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Ozdemir, Mehmet; Usta, Hakan
Electron-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.
A Solution-Processable meso-Phenyl-BODIPY-Based n-Channel Semiconductor with Enhanced Fluorescence Emission
(WILEY-V C H VERLAG GMBH, POSTFACH 101161, 69451 WEINHEIM, GERMANY, 2019) Ozcan, Emrah; Ozdemir, Mehmet; Ho, Dongil; Zorlu, Yunus; Ozdemir, Resul; Kim, Choongik; Usta, Hakan; Cosut, Bunyemin; 0000-0002-0618-1979; 0000-0002-7957-110X; 0000-0001-6530-0205; 0000-0001-6325-5674; 0000-0003-2811-1872; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
The cover feature shows the delicate balance between locally excited (LE) and twisted intramolecular charge-transfer (TICT) states, which could be controlled by solvent polarity and nano-aggregation, of a meso-phenyl-BODIPY-based fluorescent semiconductor. The dihedral angle between the meso-aromatic unit and BODIPY pi-core was found to be the key factor in this balance. This is the first report of highly emissive characteristics for an A-D-A type BODIPY-based n-channel semiconductor. Details are given in the Full Paper by B. Cosut, H. Usta, C. Kim, and co-workers (DOI: 10.1002/cplu.201900317).
Understanding 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 SOC1155 16TH ST, NW, WASHINGTON, DC 20036, 2021) Usta, Hakan; Cosut, Bunyemin; Alkan, Fahri; 0000-0002-0618-1979; 0000-0002-4046-9044; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Usta, Hakan; Alkan, Fahri
Rod-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.