Investigation of the electronic structure of the TCNQ-TTF system (original) (raw)
Related papers
Electronic structure of TCNQ, studied with HAM/3
International Journal of Quantum Chemistry, 1978
The electronic structure of tetracyanoquinodimethane (TCNQ) is calculated using the new semiempirical method HAM/3. The calculated photoelectron spectrum is in reasonable agreement with the measured spectrum. The excitation energies are obtained directly in HAM as the differences of the energies of the unoccupied and the occupied orbitals. The calculated UV spectrum is in good agreement with the measurements. The weak band at 5.3 eV, which earlier had been assumed to correspond to a forbidden transition, is allowed according to HAM. The electron affinity is also in reasonable agreement with the measured value. An explanation has been given for the experimental observation of several resonance states (negative electron affinities). p‐Quinodimethane has also been studied.
PHYSICAL REVIEW B, 2003
We report a combined experimental and theoretical study of the unoccupied electronic states of the neutral molecular organic materials TTF ͑tetrathiafulvalene͒ and TCNQ ͑7,7,8,8-tetracyano-p-quinodimethane͒ and of the one-dimensional metallic charge transfer salt TTF-TCNQ. The experimental density of states ͑DOS͒ is obtained by x-ray absorption near edge spectroscopy ͑XANES͒ with synchrotron light and the predicted DOS by means of first-principles density functional theory calculations. Most of the experimentally derived elementspecific XANES features can be associated to molecular orbitals of defined symmetry. Because of the planar geometry of the TTF and TCNQ molecules and the polarization of the synchrotron light, the energy dependent or character of the orbitals can be inferred from angular dependent XANES measurements. The present work represents the state of the art analysis of the XANES spectra of this type of materials and points out the need for additional work in order to elucidate the governing selection rules in the excitation process.
Far-Infrared Single Crystal Studies of TTF–TCNQ
physica status solidi (b), 1976
Polarized and unpolarized far-infrared (12 to 100 cm-l) reflectance data are presented for TTF-TCNQ. The results confirm the existence of the energy gap, in the conducting state a t 100 K, and in the dielectric regime a t 4.2 K and provide a quantitative measure of the residual conductivity in the gap region. The data are discussed in terms of the Peierls-Frohlich model. Analysis of the results yields an estimate for the Frohlich mass of approximately 1500 times the band effective mass and a value for the pinning frequency in the dielectric regime, OF z 2 om-l.
Theoretical study of the effects of solvents on the ground state of TCNQ
is widely used as a πacceptor for the preparation of organic charge transfer. In this paper the effect of ten solvents on the ground state of TCNQ has been reported. DFT calculations have been done on the Schrodinger software and the effect of solvents have been theoretically calculated with the help of Poisson-Boltzmann solver. The solvation energy, chemical potential, hardness, electrophilicity, HOMO-LUMO gap and the picture of the HOMO and LUMO of TCNQ in the ground state in the solvents have been reported
Electronic structure of the quasi-one-dimensional organic conductor TTF-TCNQ
Journal of Electron Spectroscopy and Related Phenomena, 2001
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Energy Level Alignment in Organic–Organic Heterojunctions: The TTF/TCNQ Interface
The Journal of Physical Chemistry C, 2013
The energy level alignment of the two organic materials forming the TTF/TCNQ interface is analyzed by means of a local orbital DFT calculation, including an appropriate correction for the transport energy gaps associated with both materials. These energy gaps are determined by a combination of some experimental data and the results of our calculations for the difference between the TTF-highest occupied molecular orbital (HOMO) and the TCNQ-lowest unoccupied molecular orbital (LUMO) levels. We find that the interface is metallic, as predicted by recent experiments, due to the overlap (and charge transfer) between the density of states corresponding to these two levels, indicating that the main mechanism controlling the TTF/TCNQ energy level alignment is the charge transfer between the two materials. We find an induced interface dipole of 0.7 eV in good agreement with the experimental evidence. We have also analyzed the electronic properties of the TTF/TCNQ interface as a function of an effective bias voltage Δ between the TCNQ and TTF crystals, finding a transition between metallic and insulator behavior for Δ ∼ 0.5 eV.
The thickness of the two-dimensional charge transfer state at the TTF-TCNQ interface
Organic Electronics, 2017
The properties of the interface between two materials can be significantly different to those of the constituents. One example is the tetrathiafulvalene (TTF) e 7,7,8,8-tetracyanoquinodimethane (TCNQ) interface, in which the interface can be metallic even though both TTF and TCNQ are wide bandgap semiconductors. Despite of its potential applications, the mechanism of the interfacial conduction remains unclear. In this work, we use ultraviolet photoemission spectroscopy and electrical measurement to determine the physical nature of the interfacial charges and the spatial extent of this interfacial state. The charge transfer state that is responsible for the interfacial conductivity is found to be quite localized. It only extends z1e2 nm away from the interface. Moreover, the electron-hole pairs at the interface are bound by Coulomb interaction to form excitons. Ohmic behavior and orders of magnitude decrease in the sheet resistance are observed by merely depositing a 2.4 nm TCNQ layer on a bulk TTF single crystal. The ultrathin nature of this highly conductive state suggests that it can be incorporated readily into ultrathin or field-effect organic devices.