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![(a) Chemical structure of TTF and TCNQ molecules and (b) schematic representation of the segregated stacking of donor and acceptor molecules in TTF-TCNQ [5].](profile/Katerina-Medjanik/publication/270650118/figure/fig1/AS:295277366923278@1447411018385/a-Chemical-structure-of-TTF-and-TCNQ-molecules-and-b-schematic-representation-of-the.png)
(a) Chemical structure of TTF and TCNQ molecules and (b) schematic representation of the segregated stacking of donor and acceptor molecules in TTF-TCNQ [5].
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The electronic structure of TTF-TCNQ was studied by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy in order to detect a spectroscopic signature of the phase transitions, especially that occurring at 54 K, which is related to a Peierls gap opening on the TCNQ stacks. All unoccupied TCNQ orbitals predicted by first-principles calcula...
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Context 1
... idea to find an ideal approach for manipulation and control of these proper- ties [1]. The history of organic conductors started more than half a century ago with the synthesis of cation radi- cal or anion radical salts built on the TCNQ acceptor or on the TTF donor, where TCNQ is 7,7,8,8-tetracyano-p- quinodimethane and TTF is tetrathiafulvalene (Fig. 1a). However the best conducting properties were achieved in the 1970s with the synthesis of the quasi-one-dimensional (1D) charge transfer compound TTF-TCNQ which com- bines these two types of molecules [2]. Its structure con- sists of segregated stacks of TTF and TCNQ molecules tilted with respect to the b axis and in opposite direc- ...
Context 2
... the best conducting properties were achieved in the 1970s with the synthesis of the quasi-one-dimensional (1D) charge transfer compound TTF-TCNQ which com- bines these two types of molecules [2]. Its structure con- sists of segregated stacks of TTF and TCNQ molecules tilted with respect to the b axis and in opposite direc- tion along the a axis, as it is shown in Figure 1b [3]. The metallic properties of TTF-TCNQ are due to a charge transfer of ρ electrons from the HOMO (highest occupied molecular orbital) band of the TTF to the LUMO (lowest a e-mail: chernenk@uni-mainz.de ...
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Citations
... The Peierls structural transition has received significant attention in Q1D crystals, as evidenced by numerous studies [10][11][12][13][14][15][16]. In the case of TTF-TCNQ crystals, intriguing observations have been made regarding this transition. ...
This research paper focuses on investigating the metal-insulator transition occurring in quasi-one-dimensional organic crystals of TTT(TCNQ)2. The study utilizes a 3D approximation approach and introduces a physical model that incorporates two essential electron-phonon interactions. The first interaction is akin to the deformation potential, while the second interaction follows a polaron type behavior. By employing the random phase approximation, the renormalized phonon spectrum is calculated across different temperatures and various values of the dimensionless Fermi momentum kF. The findings indicate that the transition exhibits characteristics of the Peierls type, and the critical temperature associated with the Peierls transition is determined. Furthermore, an interesting observation is made that the Peierls critical temperature experiences a notable decrease with an increase in carrier concentration.
... To further characterize 1-based networks transferred on a solid substrate and to establish a molecular model of the monolayer on the surface, near-edge x-ray absorption fine structure (NEXAFS) measurements at the N-K edge were carried out (Fig. 2, D to F). The spectra exhibited a very simple line shape consisting only of the signals of transitions into the p* (400.6 eV) and s* (approximately 425 eV) molecular orbitals (MOs) of CN (15,16). Only one peak is observed because the CN MO is not hybridized with the p system of the phenyl group because of the linking sp 3 -hybridized carbon (17). ...
Stable, single-nanometer thin, and free-standing two-dimensional layers with controlled molecular architectures are desired for several applications ranging from (opto-)electronic devices to nanoparticle and single-biomolecule characterization. It is, however, challenging to construct these stable single molecular layers via self-assembly, as the cohesion of those systems is ensured only by in-plane bonds. We herein demonstrate that relatively weak noncovalent bonds of limited directionality such as dipole-dipole (–CN⋅⋅⋅NC–) interactions act in a synergistic fashion to stabilize crystalline monomolecular layers of tetrafunctional calixarenes. The monolayers produced, demonstrated to be free-standing, display a well-defined atomic structure on the single-nanometer scale and are robust under a wide range of conditions including photon and electron radiation. This work opens up new avenues for the fabrication of robust, single-component, and free-standing layers via bottom-up self-assembly.
... This temperature is called the Peierls critical temperature. The Peierls transition has been studied by many authors in other Q1D organic crystals (see [10][11][12][13][14][15] and references therein). ...
The metal-insulator transition in quasi-one-dimensional organic crystals of tetrathiotetraceneiodide, TTT2I3, is investigated in 3D approximation. A more complete physical model of the crystal is applied which takes into account two the most important hole-phonon interaction mechanisms. The first is similar to that of deformation potential and the second one is of polaron type. The scattering on defects is also considered. The phonon polarization operator and the renormalized phonon spectrum are calculated in the
random phase approximation for different temperatures applying the method of retarded Green functions. The effect of lattice distortion on the dispersion of renormalized acoustic phonons is analyzed. The Peierls critical temperature is determined.
... x E E A B q n n a a u u u E ε ε (13) From Equations (12) and (13) it results the expression for the Fourier transformation of the lattice displacement Green function (14) In order to distinguish the retarded Green function it is needed to put, (16) where the principal value of the dimensionless polarization operator takes the form: ...
We investigate the metal-insulator transition in quasi-one-dimensional organic crystals of tetrathiotetracene-iodide, TTT 2 I 3 , in the 2D model. A crystal physical model is applied which takes into account two the most important hole-phonon interaction mechanisms. One is similar to that of deformation potential and the other is of polaron type. The scattering on defects is also considered and it is crucial for the explanation of the transition. The phonon polarization operator and the renormalized phonon spectrum are calculated in the random phase approximation for different temperatures applying the method of Green functions. We show that the transition is of Peierls type. The effect of lattice distortion on the dispersion of renormalized acoustic phonons is analyzed.
... In the following we report a combined experimental and theoretical study of the unoccupied electronic levels of (TMTSF) 2 PF 6 . In previous studies of molecular conductors (TTF-TCNQ, 32,34 (TMTTF) 2 AsF 6 12 ) we found that qualitative information concerning the nature, shape, and relative ordering of the unoccupied electronic levels probed by NEXAFS is needed in order to have a clear microscopic interpretation of the NEXAFS results. Here we report NEXAFS measurements and a density functional theory (DFT) investigation of (TMTSF) 2 PF 6 , and we will compare the results with those of our previous study of (TMTTF) 2 AsF 6 . ...
... Such reorganization induces some σ/π mixing in these empty levels such that a combined study of the angular and temperature dependence is required in order to fully characterize them. This is in striking contrast with the situation in the sulfur TTF-based salts like those of TMTTF 12,33 or TTF, 32,34 where the temperature dependence already allows a full characterization. ...
We present high-resolution near-edge X-ray absorption fine structure (NEXAFS) measurements at the P L2/3-edges, F K-edge, C K-edge and Se M2/3-edges of the quasi-one-dimensional (1D) conductor and superconductor (TMTSF)2PF6. NEXAFS allows probing the donor and acceptor moieties separately; spectra were recorded between room temperature (RT) and 30 K at normal incidence. Spectra taken around RT were also studied as a function of the angle () between the electric field of the X-ray beam and the 1D conducting direction. In contrast with a previous study of the S L2/3-edges spectra in (TMTTF)2AsF6, the Se M2/3-edges of (TMTSF)2PF6 do not exhibit a well resolved spectrum. Surprisingly, the C K-edge spectra contain three well defined peaks exhibiting strong and non-trivial and temperature dependence. The nature of these peaks as well as those of the F K-edge spectra could be rationalized on the basis of first-principles DFT calculations. Despite the structural similarity, the NEXAFS spectra of (TMTSF)2PF6 and (TMTTF)2AsF6 exhibit important differences. In contrast with the case of (TMTTF)2AsF6, the F K-edge spectra of (TMTSF)2PF6 do not change with temperature despite stronger donor-anion interactions. All these features reveal subtle differences in the electronic structure of the TMTSF and TMTTF families of salts.
... In the following we report a combined experimental and theoretical study of the unoccupied electronic levels of (TMTSF) 2 PF 6 . In previous studies of molecular conductors (TTF-TCNQ, 32,34 (TMTTF) 2 AsF 6 12 ) we found that qualitative information concerning the nature, shape, and relative ordering of the unoccupied electronic levels probed by NEXAFS is needed in order to have a clear microscopic interpretation of the NEXAFS results. Here we report NEXAFS measurements and a density functional theory (DFT) investigation of (TMTSF) 2 PF 6 , and we will compare the results with those of our previous study of (TMTTF) 2 AsF 6 . ...
... Such reorganization induces some σ/π mixing in these empty levels such that a combined study of the angular and temperature dependence is required in order to fully characterize them. This is in striking contrast with the situation in the sulfur TTF-based salts like those of TMTTF 12,33 or TTF, 32,34 where the temperature dependence already allows a full characterization. ...
We present high-resolution near-edge X-ray absorption fine structure (NEXAFS) measurements at the P L2/3 edges, F K edge, C K edge, and Se M2/3 edges of the quasi one- dimensional (1D) conductor and superconductor (TMTSF)2PF6. NEXAFS allows probing the donor and acceptor moieties separately; spectra were recorded between room temperature (RT) and 30 K at normal incidence. Spectra taken around RT were also studied as a function of the angle (θ) between the electric field of the X-ray beam and the 1D
conducting direction. In contrast with a previous study of the S L2/3-edges spectra in (TMTTF)2AsF6, the Se M2/3 edges of (TMTSF)2PF6 do not exhibit a well-resolved spectrum. Surprisingly, the C K-edge spectra contain three well-defined peaks exhibiting strong and nontrivial θ and temperature dependence. The
nature of these peaks as well as those of the F K-edge spectra could be rationalized on the basis of first-principles DFT calculations. Despite the structural similarity, the NEXAFS spectra of (TMTSF)2PF6 and (TMTTF)2AsF6 exhibit important differences. In contrast with the case of (TMTTF)2AsF6, the F K-edge spectra of (TMTSF)2PF6 do not change with temperature despite stronger donor−anion interactions. All these features reveal subtle differences in the electronic structure of the TMTSF and TMTTF families of salts.
... In the following we report a combined experimental and theoretical study of the unoccupied electronic levels of (TMTSF) 2 PF 6 . In previous studies of molecular conductors (TTF-TCNQ, 32,34 (TMTTF) 2 AsF 6 12 ) we found that qualitative information concerning the nature, shape, and relative ordering of the unoccupied electronic levels probed by NEXAFS is needed in order to have a clear microscopic interpretation of the NEXAFS results. Here we report NEXAFS measurements and a density functional theory (DFT) investigation of (TMTSF) 2 PF 6 , and we will compare the results with those of our previous study of (TMTTF) 2 AsF 6 . ...
... Such reorganization induces some σ/π mixing in these empty levels such that a combined study of the angular and temperature dependence is required in order to fully characterize them. This is in striking contrast with the situation in the sulfur TTF-based salts like those of TMTTF 12,33 or TTF, 32,34 where the temperature dependence already allows a full characterization. ...
We present high-resolution near-edge X-ray absorption fine structure (NEXAFS) measurements at the P
L2/3 edges, F K edge, C K edge, and Se M2/3 edges of the quasi one- dimensional (1D) conductor and superconductor (TMTSF)2PF6. NEXAFS allows probing the donor and acceptor moieties separately; spectra were recorded between room temperature (RT) and 30 K at normal incidence. Spectra taken
around RT were also studied as a function of the angle (θ) between the electric field of the X-ray beam and the 1D conducting direction. In contrast with a previous study of the S L2/3-edges spectra in (TMTTF)2AsF6, the Se M2/3 edges of (TMTSF)2PF6 do not exhibit a well-resolved spectrum. Surprisingly, the C K-edge spectra contain three well-defined peaks exhibiting strong and nontrivial θ and temperature dependence. The
nature of these peaks as well as those of the F K-edge spectra could be rationalized on the basis of first-principles DFT calculations. Despite the structural similarity, the NEXAFS spectra of (TMTSF)2PF6 and (TMTTF)2AsF6 exhibit important differences. In contrast with the case of (TMTTF)2AsF6, the F K-edge spectra of (TMTSF)2PF6 do not change with temperature despite stronger donor−anion interactions. All these features reveal subtle differences in the electronic structure of the TMTSF and TMTTF families of salts.
... Neither the N 2p density of states (DOS) on an atom in the molecule (shaded region in Fig. 6(a)) nor its convoluted form (red line) reproduces the measured NEXAFS spectra. Previous works 15,35 used this approach to identify the origin of the peaks observed in NEXAFS. However, in order to reach a reasonable agreement between theory and experiment, assumptions on energy shifts and on the absence of certain peaks in NEXAFS were necessary. ...
Transition-density-fragment interaction combined with transfer integral approach for excitation-energy transfer via charge-transfer states J. Chem. Phys. 137, 034101 (2012); 10.1063/1.4733669 C–C bond unsaturation degree in monosubstituted ferrocenes for molecular electronics investigated by a combined near-edge x-ray absorption fine structure, x-ray photoemission spectroscopy, and density functional theory approach J. Chem. Phys. 136, 134308 (2012); 10.1063/1.3698283 Charging energy and barrier height of pentacene on Au(111): A local-orbital hybrid-functional density functional theory approach J. Chem. Phys. 135, 084702 (2011); 10.1063/1.3626522 Time dependent density functional theory study of the near-edge x-ray absorption fine structure of benzene in gas phase and on metal surfaces We have investigated the charge transfer mechanism in single crystals of DTBDT-TCNQ and DTBDT-F 4 TCNQ (where DTBDT is dithieno[2,3-d;2 ′ ,3 ′-d ′ ] benzo[1,2-b;4,5-b ′ ]dithiophene) using a combination of near-edge X-ray absorption spectroscopy (NEXAFS) and density functional theory calculations (DFT) including final state effects beyond the sudden state approximation. In particular, we find that a description that considers the partial screening of the electron-hole Coulomb correlation on a static level as well as the rearrangement of electronic density shows excellent agreement with experiment and allows to uncover the details of the charge transfer mechanism in DTBDT-TCNQ and DTBDT-F 4 TCNQ, as well as a reinterpretation of previous NEXAFS data on pure TCNQ. Finally, we further show that almost the same quality of agreement between theoretical results and experiment is obtained by the much faster Z+1/2 approximation, where the core hole effects are simulated by replacing N or F with atomic number Z with the neighboring atom with atomic number Z+1/2. Published by AIP Publishing. [http://dx.
... It has been also mentioned that the highly conducting Q1D organic crystals may have very prospective thermoelectric applications [4] [5]. The charge transfer compound TTF-TCNQ (tetrathiafulvalene-tetracyanoquinodimethane) is the most investigated Q1D organic crystal with the high electrical conductivity [6]. Its structure consists of segregated chains or stacks of TTF and TCNQ molecules. ...
The Peierls structural transition in quasi-one-dimensional organic crystals of TTF-TCNQ is investigated in the frame of a more complete physical model. The two most important electron-phonon interaction mechanisms are taken into account simultaneously. One is similar of that of deformation potential and the other is of polaron type. For simplicity, the 2D crystal model is considered. The renormalized phonon spectrum and the phonon polarization operator are calculated in the random phase approximation for different temperatures. The effects of interchain interaction on renormalized acoustic phonons and on the Peierls critical temperature are analyzed.
We herein report a novel square-planar complex [CoIIL], which was synthesized using the electronically interesting phenalenyl-derived ligand LH2 = 9,9'-(ethane-1,2-diylbis(azanediyl))bis(1H-phenalen-1-one). The molecular structure of the complex is confirmed with the help of the single-crystal X-ray diffraction technique. [CoIIL] is a mononuclear complex where the Co(II) ion is present in the square-planar geometry coordinated by the chelating bis-phenalenone ligand. The solid-state packing of [CoIIL] complex in a crystal structure has been explained with the help of supramolecular studies, which revealed that the π···π stacking present in the [CoIIL] complex is analogous to the one present in tetrathiafulvalene/tetracyanoquinodimethane charge transfer salt, well-known materials for their unique charge carrier interfaces. The [CoIIL] complex was employed as the active material to fabricate a resistive switching memory device, indium tin oxide/CoIIL/Al, and characterized using the write-read-erase-read cycle. The device has interestingly shown a stable and reproducible switching between two different resistance states for more than 2000 s. Observed bistable resistive states of the device have been explained by corroborating the electrochemical characterizations and density functional theory studies, where the role of the CoII metal center and π-conjugated phenalenyl backbone in the redox-resistive switching mechanism is proposed.
