Bünyemin Çoşut

Solution-Processable BODIPY-Based Small Molecules for Semiconducting Microfibers in Organic Thin-Film Transistors

Electron-deficient π-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 π-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 (1)H/(13)C 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·s and current on/off ratios of >10(8). Film microstructural and morphological characterizations indicate the formation of relatively long (∼0.1 mm) and micrometer-sized (1-2 μm) crystalline fibers for BDY-4T-BDY-based films along the shearing direction. Fiber-alignment-induced charge-transport anisotropy (μ∥/μ⊥ ≈ 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.

Absolute structure determination as a reference for the enantiomeric resolution of racemic mixtures of cyclophosphazenes via chiral high-performance liquid chromatography

Reversed-phase chiral high-performance liquid chromatography (HPLC) is a potentially powerful technique for the enantiomeric resolution of racemic mixtures, although the elution order of enantiomers is only relative and it is necessary to fully characterize reference systems for this method to provide absolute configurational information. The enantiomeric resolution of a series of racemic di-spiro cyclotriphosphazene derivatives, N3P3X2[O(CH2)(3)NH]2 (X = Cl, Ph, SPh, NHPh, OPh) [(1)-(5), respectively] was carried out by reversed-phase chiral HPLC on a commercially available Pirkle-type chiral stationary phase (R,R)-Whelk-01 using 85:15 (v/v) hexane-thf as the mobile phase. The absolute configurations of the resulting enantiomers of compounds (3) (X = SPh) and (5) (X = OPh) were determined unambiguously by X-ray crystallography. For both (3) and (5) it was found that the SS enantiomer eluted before the RR enantiomer, indicating a convenient method to determine the absolute configurations of enantiomers of this series of cyclophosphazene derivatives and providing the first set of enantiomeric reference compounds for cyclophosphazene derivatives. These structures demonstrate an interesting anomaly in that the pair of enantiomers of (3) crystallize in enantiomorphically paired space groups whilst, under the same conditions, the solid-state forms of the enantiomers of (5) form structures in Sohncke space groups that are not enantiomorphous.

A new rod-shaped BODIPY-acetylene molecule for solution-processed semiconducting microribbons in n-channel organic field-effect transistors

BODIPY-based π-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 π-acceptors and a rod-shaped 1,4-bis-(thienylethynyl)2,5-dialkoxybenzene π-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 (θ = 44.94°), antiparallel π-stacked BODIPY dimers with an interplanar distance of 3.93 A, and strong “C–H⋯π (2.85 A)” 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 cm2 V−1 s−1 and an on/off current ratio of 105–106. 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 π-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.

Nitronyl and imino nitroxide free radicals as precursors of magnetic phthalocyanine and porphyrin building blocks

Phthalonitrile and benzaldehyde bearing α-nitronyl and α-imino nitroxide free radicals have been synthesized as precursors of nitroxide substituted phthalocyanine and porphyrin macrocycles. To ascertain the structure and radical type they have been characterized by single crystal X-ray crystallography and by electron paramagnetic resonance spectroscopy (EPR). Their EPR spectra coincide with those reported for previous nitroxides and are in good agreement with literature. Electrospray ionization mass spectroscopy (ESI) was used as a complementary and an alternative technique. Depending on the nature of the radical, two ionization behaviors have been underscored; imino radicals were detected as the [MH2]+ cation ions and nitroxide radicals were detected as the [MH]+˙ radical cations. This differentiation is pointed out as an efficient and rapid method for preliminary characterization of the radical moieties and a judicious technique that allows the prompt detection of radicals at low concentration and straightforward confirmation of the structure.

Synthesis, photophysical, DFT and photodiode properties of subphthalocyanine–BODIPY dyads

In this study, subphthalocyanine–borondipyrromethene conjugates have been successfully designed and synthesized. The novel compounds were fully characterized by using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and 1H and 13C NMR spectroscopies. The photophysical properties of the conjugates were investigated by means of absorption and fluorescence spectroscopies in benzene solutions. The results showed that while the absorption spectra of both conjugates remain almost the same, compound 5 has a better fluorescence behavior and higher energy transfer efficiency. To test the effect of the replacement of the methyl group in the conjugates, Density functional theory (DFT) was used to calculate the equilibrium geometries of the ground state for the conjugates. The torsional angle of the BODIPY with reference to Sub-Pc in compound 5 (−125.4°) was different than that in compound 6 (−91.4°). This planarization results in a decrease in the orbital energy of the BODIPY unit in compound 5, making a smaller gap for the energy transfer mechanism between the BODIPY and Sub-Pc unit. In addition, their photodiode properties were tested here. The obtained phototransient current and capacitance results indicated that the devices exhibit both photodiode and photocapacitor properties. Therefore, it can be concluded that the subphthalocyanine–borondipyrromethene conjugate-based photodevices can be used as photodiodes in solar tracking systems.

Mimicking cellular phospholipid bilayer packing creates predictable crystalline molecular metal–organophosphonate macrocycles and cages

We report a novel mechanism to create a predictable molecular metal–organophosphonate cage [Zn2(2,2′-bpy)2(H2ODP)2(H4ODP)]·2H2O (1·2H2O) (H4ODP = 1,8-octanediphosphonic acid) and a macrocycle [Cu2(2,2′-bpy)2(H2-1,4-NDPA)2(H2O)2]·H2O (2) (H4-1,4-NDPA = 1,4-naphthalene diphosphonic acid). The structures were solved using single crystal X-ray diffraction. The photoluminescence properties of 1·2H2O, investigated both in solution and in the solid-state at room temperature, indicated that the tighter zinc binding in the solid state leads to the augmentation of fluorescence. The ORCA molecular structure optimization calculations for 1·2H2O suggest a slight opening of the cage structure in non-polar solvents while in polar solvents the cage is tightened. Toxicity analysis with Caco-2 cells indicates that the molecule is readily tolerated by intestinal cells.

The Preparation of Transparent Organic Field Effect Transistor Using a Novel EDOT Functional Styrene Copolymer Insulator With a PEDOT:PSS Gate Electrode

In this study, we have purposed to combine both polystyrene (PS) and 3,4-ethylenedioxythiophene (EDOT) groups as a gate dielectric and to fabricate a transparent organic field effect transistor (OFET) device with polymeric gate electrode using this novel organic dielectric material. The focus point of this work is to obtain a transparent OFET and to minimize the interface states between gate insulator and gate electrode. Firstly, we have synthesized EDOT functional polystyrene (PS-EDOT) copolymer as gate insulator via “click” chemistry between azide-functional styrene copolymer and propargyl-functionalized EDOT. We used the poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) conductive polymer mixture as a suitable alternative gate electrode instead of inorganic contacts, which is a new topic in the organic electronics. The contact resistance value was measured as 1/600 (S/cm)-1. At the end of the process transparent OFETs with different channel length were fabricated using spin coating method by which poly(3-hexylthiophene) (P3HT), novel PS-EDOT copolymer insulator and PEDOT:PSS were coated on prepatterned OFET substrate. Electrical characterizations of OFET devices were held in total darkness and in air ambient in order to achieve output and transfer current-voltage (I-V) characteristics. The main parameters such as the threshold voltage (VTh), field effect mobility (μFET) and current on/off ratio (Ion/off) of the devices were extracted from capacitance-frequency (C-f) plot. It was found that fabricated PS-EDOT OFETs exhibit good device performances such as low VTh, remarkable mobility, and Ion/off values.