(Perylene)3-(TCNQF1)2: Yet Another Member in the Series of Perylene–TCNQFx Polymorphic Charge Transfer Crystals (original) (raw)
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Structure, Stoichiometry, and Charge Transfer in Cocrystals of Perylene with TCNQ-Fx
Crystal Growth & Design, 2016
Semiconductor charge transfer (CT) cocrystals are an emerging class of molecular materials which combines the characteristics of the constituent molecules in order to tune physical properties. Cocrystals can exhibit polymorphism, but different stoichiometries of the donor-acceptor (DA) pair can also give different structures. In addition, the structures of the donor and acceptor as pristine compounds can influence the resulting cocrystal forms. We report a structural study on several CT cocrystals obtained by combining the polyaromatic hydrocarbon perylene with 7,7,8,8-tetracyanoquinodimethane (TCNQ) and its fluorinated derivatives having increasing electronegativity. This is achieved by varying the amount of fluorine substitution on the aromatic ring, with TCNQ-F 2 and TCNQ-F 4. We find structures with different stoichiometries. Namely, the system perylene:TCNQ-F 0 is found with ratios 1:1 and 3:1, while the systems perylene:TCNQ-F x (x=2,4) are found with ratios 1:1 and 3:2. We discuss the structures on the basis of the polymorphism of perylene as pure compound, and show that by a judicious choice of growth temperature the crystal structure can be in principle designed a priori. We also analyse the structural motifs taking into account the degree of charge transfer between the perylene donor and the TCNQ-F x acceptors and the optical gap determined
New Polymorphs of Perylene:Tetracyanoquinodimethane Charge Transfer Cocrystals
Crystal Growth & Design, 2018
We report two hitherto unknown polymorphs of the charge transfer (CT) cocrystal perylene:tetracyanoquinodimethane (TCNQ) grown by physical vapour transport (PVT) in argon atmosphere. One of the polymorphs, named , has stoichiometry 1:1 and adds to the three known structures with stoichiometry 1:1 (), 2:1 and 3:1. Interestingly, below (280 ± 10) K the structure undergoes a phase transition to what we refer to as the γ polymorph, with halving of the unit cell and reduction of symmetry from monoclinic to triclinic. Both new crystal structures present two alternating stacks with different intermolecular and intramolecular geometries. In stack S-I the perylene molecules show substantial deviations from planarity, with the angle between the naphthalene intramolecular moieties of 6.69º, and with the perylene and TCNQ molecular centroids shifted by 1.95 Å. In the second stack, S-II, the perylene is planar and the centroids almost coincident. Structural investigations on bond length complemented by vibrational IR spectroscopy indicate that in the new polymorphs the degree of charge transfer, can be 0 or 0.12. The higher value of ionicity to be due to donoracceptor pairs in the S-II, while molecules in S-I are closer to neutrality. Thus the ionicity of the donor-acceptor pair depends on the stack and is comparable to that one of the polymorph which we redetermined as = ± .
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.
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.
The Stoichiometry of TCNQ-Based Organic Charge-Transfer Cocrystals
Crystals, 2020
Organic charge-transfer cocrystals (CTCs) have attracted significant research attention due to their wide range of potential applications in organic optoelectronic devices, organic magnetic devices, organic energy devices, pharmaceutical industry, etc. The physical properties of organic charge transfer cocrystals can be tuned not only by changing the donor and acceptor molecules, but also by varying the stoichiometry between the donor and the acceptor. However, the importance of the stoichiometry on tuning the properties of CTCs has still been underestimated. In this review, single-crystal growth methods of organic CTCs with different stoichiometries are first introduced, and their physical properties, including the degree of charge transfer, electrical conductivity, and field-effect mobility, are then discussed. Finally, a perspective of this research direction is provided to give the readers a general understanding of the concept.
Structure and Transport Properties of the Charge-Transfer Salt Coronene−TCNQ
Chemistry of Materials
Coronene is a highly symmetric organic molecule whose molecular structure resembles a fragment of graphite. We have crystallized a charge-transfer complex based on coronene and TCNQ, and present crystal structure and transport properties. The complex adopts alternate stacking between coronene and TCNQ, and the charge-transfer was estimated to be of the order of 0.3 by the structure and IR analysis of TCNQ. This degree of chargetransfer is larger than those of other hydrocarbon based charge-transfer complexes reported. We find semiconductor behavior with an optical gap of 1.55 eV and a transport gap of 0.49 eV. The Child's law mobility is estimated to be 0.3 cm 2 /Vssthis along with the small transport gap suggests this compound might be attractive for device applications.
In organic electronics and optoelectronics several crucial physical processes are related to charge transfer (CT) effects. In this work, we investigate mixing behavior and intermolecular coupling of donor and acceptor molecules in thin films prepared by organic molecular beam deposition (OMBD). Diindenoperylene (DIP) and pentacene (PEN) are used as the donor materials, and perylene diimide derivatives PDIR-CN 2 and PDIF-CN 2 as the acceptor materials.. The formation of charge transfer complexes coupled in the electronic excited state vs. noninteracting phase separating components is studied by structural and optical techniques. The CT mechanism and properties are considered in close connection with the thin film microstructure of the D/A blends which can be controlled via a change of the molecule geometry and/or growth temperature. We discuss two key findings for our systems: (1) The CT intensity correlates directly with the possibility of cocrystallization between acceptor and donor. (2) Side chain modification to tune the ground state energy levels has nearly no effect on the energy of the excited state CT, whereas replacement of molecular core modifies the CT energy correspondingly.
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.