TetramethylbenzidineTetrafluoroTCNQ (TMBTCNQF4): A Narrow-Gap Semiconducting Salt with Room-Temperature Relaxor Ferroelectric Behavior (original) (raw)
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The Journal of Physical Chemistry C, 2021
Charge-transfer crystals exhibit unique electronic and magnetic properties with interesting applications. The chargetransfer single crystal formed by dibenzotetrathiafulvalene (DBTTF) together with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) presents a long-range ordered supramolecular structure of segregated stacks, with a unitary degree of charge transfer. Thus, the crystal structure is composed of dimerized radical molecules with unpaired electrons. The energy levels and the spin degrees of freedom of this material were investigated by solid-state electrochemistry and electron paramagnetic resonance (EPR) spectroscopy. The electrochemical data, supported by density functional theory calculations, show how this organic Mott insulator has an electronic gap in the range of hundreds of meV. EPR experiments show the presence of a ground-state S = 1 triplet spin state along with localized S = 1/2 spins. The calculations also predict a ground-state triplet configuration, with the singlet configuration at 170 meV higher energy. DBTTF/F4TCNQ seems to be a candidate material for organic electronic and spintronic applications.
Chemistry (Weinheim an der Bergstrasse, Germany), 2017
Ferroelectric materials find extensive applications in the fabrication of compact memory devices and ultra-sensitive multifunctional detectors. Face-to-face alternate stacking of electron donors and acceptors effectuate long-range unidirectional ordering of charge transfer (CT) dipoles, promising tunable ferroelectricity. Herein we report a new TTF-quinone system - an emerald green CT complex consisting pillar[5]quinone (P5Q) and tetrathiafulvalene (TTF). The CT crystals, as determined by single crystal synchrotron X-ray diffraction, adopt a 1:1 mixed-stack arrangement of donor and acceptor with alternating dimers of TTF and 1,4-dioxane encapsulated P5Q. The TTF-P5Q.dioxane crystal possesses a macroscopic polarization axis giving rise to ferroelectricity at room temperature. The CT complex manifests ferroelectric features such as optical polarization rotation, temperature-dependent phase transition and piezoelectric response in single crystals. Ferroelectric behavior observed in P5Q...
Advanced Electronic Materials, 2016
The organic charge-transfer (CT) complex dibenzotetrathiafulvalene-7,7,8,8tetracyanoquinodimethane (DBTTF-TCNQ) is found to crystallize in two polymorphs when grown by physical vapor transport: the known α-polymorph and a new structure, the β-polymorph. Structural and elemental analysis via selected area electron diffraction (SAED), X-ray photoelectron spectroscopy (XPS), and polarized IR spectroscopy reveal that the complexes have the same stoichiometry with a 1:1 donor:acceptor ratio, but exhibit unique unit cells. The structural variations result in significant differences in the optoelectronic properties of the crystals, as observed in our experiments and electronic-structure calculations. Raman spectroscopy shows that the α-polymorph has a degree of charge transfer of about 0.5e, while the β-polymorph is nearly neutral. Organic field-effect transistors fabricated on these crystals reveal that in the same device structure both polymorphs show ambipolar charge transport, but the α-polymorph exhibits electron-dominant transport while the β-polymorph is hole-dominant. Together, these measurements imply that the transport features result from differing donor-acceptor overlap and consequential varying in frontier molecular orbital mixing, as suggested theoretically for chargetransfer complexes.
2021
Stefano Canossa, Elena Ferrari, Pit Sippel, Jonas K. H. Fischer, 4 Raphael Pfattner, Ruggero Frison, Matteo Masino, Marta Mas-Torrent, Peter Lunkenheimer, Concepció Rovira, and Alberto Girlando∗2, 7 EMAT, Department of Physics, University of Antwerp, 2020 Antwerp, Belgium Dipartimento di Scienze Chimiche, della Vita e della Sostenibilità Ambientale (S.C.V.S.A.) & INSTM-UdR Parma, Università di Parma, 43124 Parma, Italy Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany Tohoku Forum for Creativity, Tohoku University, 980-8577 Sendai, Japan Department of Molecular Nanoscience and Organic Materials, Institut de Ciència de Materials de Barcelona (ICMAB-CSIC) and Networking Research Center on Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), ES-08193 Bellaterra, Spain Physik-Institut, Universität Zürich, 8057 Zürich, Switzerland Present address: Molecular Materials Group, 43124 Parma, Italy
Mixed Stack Organic Semiconductors: The Anomalous Case of the BTBT-TCNQFx Series
Crystal Growth & Design
We report on a series of charge-transfer (CT) crystals where BTBT electron donor is associated with TCNQF x (x = 0, 2, 4). At variance with Perylene-TCNQF x series, the degree of CT ρ does not increase with TCNQF x electron affinity. The anomaly is explained by the involvement of BTBT HOMO and HOMO−1 in the CT mechanism and by the Madelung energy behavior.
Chemistry - A European Journal, 2014
A compact and planar donor-acceptor molecule 1 comprising tetrathiafulvalene (TTF) and benzothiadiazole (BTD) has been synthesised and experimentally characterised by structural, optical and electrochemical methods. Solution processed and thermally evaporated thin films of 1 have also been explored as active material in organic field-effect transistors (OFETs). For these devices, a hole field-effect mobility of FE = (1.3 ± 0.5) ×10-3 cm 2 /Vs and of FE = (2.7 ± 0.4) ×10-3 cm 2 /Vs could be determined for the solution processed and thermally evaporated thin films, respectively. An intense intramolecular charge-transfer (ICT) transition around 495 nm dominates the optical absorption spectrum of the neutral dyad, which also shows a weak emission from its ICT state. The iodine induced oxidation of 1 leads to a partially oxidised crystalline charge-transfer (CT) salt {(1) 2 I 3 }, and eventually also to a fully oxidized compound {1I 3 } ½I 2. Single crystals of the former CT compound, exhibiting a highly symmetrical crystal structure, reveal a fairly good room temperature electrical conductivity of the order of 2 S cm-1. The one-dimensional spin system bears compactly bonded BTD acceptors (spatial localisation of LUMO) along its ridge.
Ionicity Phase Diagram of Trifluoromethyl-TCNQ (CF3TCNQ) Charge-Transfer Solids
Bulletin of the Chemical Society of Japan, 2010
A series of charge-transfer (CT) solids of trifluoromethyl-7,7,8,8-tetracyanoquinodimethane (CF 3 TCNQ) with various electron donor molecules were prepared and their IR and UVvisnear-IR spectra and electrical conductivity were measured. The information was applied to produce an ionicity phase diagram of CF 3 TCNQ CT solids. A boundary for ionicity of CF 3 TCNQ was found in combination with donor molecules of dibenzo[c,d]phenothiazine, diaminodurene, or dibenzotetrathiafulvalene (DBTTF). With stronger donors than DBTTF, the CF 3 TCNQ molecules were fully ionized and acted as a counter anion. No conductors with partially charged CF 3 TCNQ species were obtained. Besides the conventional 1:1 fully ionic insulators with segregated stacks, tetramethyl-TTF¢CF 3 TCNQ¢CH 3 CN and bis(methylthio)ethylenedithio-TTF¢CF 3 TCNQ had fully ionic alternating stacks of DDAA units and showed Frenkel triplet excitons. (BEDO-TTF) 2 (CF 3 TCNQ) [BEDO-TTF: bis(ethylenedioxy)-TTF] consisted of a mixed-valence segregated stack of donor molecules and completely ionized acceptor molecules, and showed metallic behavior down to 1.8 K even in a compressed pellet sample. LangmuirBlodgett films composed of (BEDO-TTF) 2 (CF 3 TCNQ) and matrix (arachidic acid) showed a conductivity of 36 S cm ¹1 at room temperature and a nearly temperature-independent conductivity down to 80 K. Semiconducting (TMTSF) 2 (CF 3 TCNQ) (TMTSF: tetramethyltetraselenafulvalene) had one-dimensional segregated stacks of dimerized TMTSF molecules separated by completely ionized CF 3 TCNQ, the molecular plane of which was arranged parallel to the TMTSF column. The ionicity phase diagram of the CF 3 TCNQ CT solids, i.e., a plot of the first CT transition energy vs. donor strength, clearly discriminated these different kinds of CT solids and will be utilized for the prediction and design of the functional CT solids.
Magnetism and Charge ordering in TMTTF $ _2 −PF-PF −PF _6 $ organic crystals
Arxiv preprint arXiv: …, 2011
Using a combination of Density Functional Theory, mean-field analysis and exact diagonalization calculations we reveal the emergence of a dimerized charge ordered state in TMTTF2-PF6 organic crystal. The interplay between charge and spin order leads to a rich phase diagram. Coexistence of charge ordering with a structural dimerization results in a ferroelectric phase, which has been observed experimentally. The tendency to the dimerization is magnetically driven revealing TMTTF2-PF6 as a multiferroic material. PACS numbers: 71.30.+h, 71.45.Lr, 71.20.Rv In recent years, organic molecular crystals have emerged as a fascinating class of materials with immense potential for applications. Structures in these materials are held together by van der Waals and hydrogen bonding as opposed to much stronger covalent and ionic bonding in conventional crystals. As a consequence, these systems present complex phases and phenomena which still require a microscopic understanding, ranging from anomalous positive and negative thermal expansion[1] to hightemperature ferroelectricity with large polarization[2] and even superconductivity . Moreover, their light, flexible and nontoxic character makes them ideal candidates for future applications.
Synthetic Metals, 2005
Four new radical cation salts based on the amide functionalized EDT-TTF organic donors EDT-TTF-CONH 2 (D1) and EDT-TTF-(CONH 2 ) 2 (D2), ␣ -(D1) 4 [FeNO(CN) 5 ] (1), ␣ -(D1) 4 [Co(CN) 6 ] (2), -(D1) 6 [Fe(CN) 6 ] (3) and (D2) 4 [FeNO(CN) 5 ]NB (4), have been synthesized and characterized by X-ray single crystal diffraction experiments, band structure calculations and electrical resistivity measurements. Functionalized organic donors are remarkable for the ability to form cation· · ·cation and cation· · ·anion type hydrogen bonds which can effectively direct the crystal architecture of molecular conductors. The structural analysis reveals a well-developed hydrogen bond network in the crystals investigated. (D1) 2 -dimers or (D2) n -extended zigzag chains of donors connected through functional groups are found to be stable structural motifs in 1-4. Remarkably, salts 1 and 2 are isostructural despite the presence of anions of different charge (−2 and −3, respectively) and the inherent difference in the degree of charge transfer has a clear effect on the transport properties: σ RT (2)/σ RT (1) = 300. Salt 3 differs from 1 and 2 both in the stoichiometry and packing of the conducting organic layer. Crystals of 4 exhibit a superstructure with the incommensurate vector q = ±(0.5, 0.3, 0.2).
Polyhedron, 2006
A new charge transfer salt (TCN-DBTTF)[Fe(H 2 O) 6 ][FeBr 4 ] 3 (1) (TCN-DBTTF:tetracyanodibenzotetrathiafulvalene) has been synthesized by electrocrystallization and structurally characterized. The compound crystallizes in the monoclinic space group C2/c, M = 1694.91, a = 35.759(3) Å , b = 9.9966(6) Å , c = 12.1129(10) Å , b = 98.350(7)°, V = 4284.1(6) Å 3 and Z = 4. The compound is composed of three types of paramagnetic spin carriers: oxidized TCN-DBTTF radicals (S = 1/2), [Fe(H 2 O) 6 ] 2+ cations (S = 2) and [FeBr 4 ] À anions (S = 5/2). Due to the specific crystal packing, an electrical conductivity at room temperature in the order of only 10 À7 S cm À1 is observed and magnetic measurements reveal overall antiferromagnetic interactions among the three different spin centers. S S S S NC NC CN CN Tetracyanodibenzotetrathiafulvalene (TCN-DBTTF) Ó