Tetrathiafulvalene Molecules Research Articles

Highly efficient organic-graphene hybrid photodetectors via molecular peripheral editing.

Hybrid systems based on graphene and organic molecules are highly appealing for "correcting" the limited optoelectronic properties of 2D materials. However, an in-depth understanding of the correlation between the structure of the molecular sensitizer and the physical properties of the hybrid toward high-performance organic-graphene hybrid photodetectors remains elusive. Herein, an ad hoc molecular design via a peripheral editing approach on the organic molecules is employed to elucidate the structure-property relationship when interfaced with graphene forming hybrid systems. Efficient doping of graphene can be attained by physisorption of tetrathiafulvalene molecules exposing electron-donating peripheral groups, benefiting from a strong coupling yielding efficient charge transfer, ultimately leading to photodetectors with an ultra-high responsivity of 1.1 × 107 A W-1 and a specific detectivity of 6.5 × 1014 Jones, thereby outperforming state-of-the-art graphene-based photodetectors. These results offer valuable insights for future optimization of graphene-based photodetectors through molecular functionalization.

Interface design of the thermoelectric transport properties of phosphorene-tetrathiafulvalene nanoscale devices.

Interface design and energy band engineering are two key strategies for improving the thermoelectric conversion efficiency of low dimensional nanoscale devices. By using first-principle-based density functional theory combined with a non-equilibrium Green function method, the thermoelectric properties of a single tetrathiafulvalene (TTF) molecule coupled with armchair phosphorene nanoribbons (APNRs) within different interface modes have been investigated. The results indicate that phonon transport can be dramatically suppressed in this intermediate weak-coupling system due to strong interfacial phonon scattering behavior, where very few phonons can propagate through two nonbonded interface regions from left side lead to a TTF molecule and then to right side lead. Furthermore, connecting a thiophene group at both the head and tail of the intermediate TTF molecule can significantly enhance the power factor (S2σ) of such a weak-coupling system based on an out-of-plane electronic transmission mechanism, and there is obvious charge transfer from S atoms to upper and lower APNRs. Compared to a single regular method, composite interface co-design can achieve more accurate control of thermal/electrical transmission performance. Electrical conductance can be effectively improved with low phonon thermal conductance being maintained at the same time, and an excellent thermoelectric figure of merit (ZT) of 0.73 has been obtained near 0.6 eV.

Electronic structures and molecular doping of germanane regulated by hydrogen vacancy clusters

Germanane is expected to substitute for existing silicon-based or germanium-based material. Germanane is regarded as an ideal candidate for next-generation semiconductor material due to its suitable band gap, high electron mobility, better environmental stability, small electrical noise and ultrathin geometry. In this work, the effects of different configuration and concentration of hydrogen vacancy cluster on the electronic properties of germanane and its molecular doping are systematically investigated through the first-principles method based on density functional theory and none-quilibrium Green’s function. The results show that the hydrogen vacancy clusters with different configurations can induce magnetism with different characteristics in Germanane<sub>Dehydrogenated-<i>x</i>H</sub> (G<sub>D-<i>x</i>H</sub>) system, and the magnetic moments are consistent with the predictions of Lieb’s theorem. Moreover, the p-type-liked doping effects caused by defective state under G<sub>D-<i>x</i>H</sub> (<i>x</i> = 1, 4, 6) systems can be realized in their spin-down band structures. The corresponding energy values for exciting electron would gradually decrease with the increase of the concentration of hydrogen vacancy clusters under different configurations. After adsorbing tetrathiafulvalene (TTF) molecules, G/TTF and G<sub>D-<i>x</i>H</sub>/TTF (<i>x</i> = 1, 2, 6) systems exhibit molecular doping characteristics induced by the TTF molecules. More importantly, for G<sub>D-<i>x</i>H</sub>/TTF (<i>x</i> = 1, 6) system, the different molecular doping types can be introduced in spin-up and spin-down band structures due to the hybridization composed of molecular orbitals and defective states under spin polarization. Further calculations of their transport properties indicate that germanane-based device with Armchair and Zigzag configurations both exhibit intensive isotropy, and the performance of <i>I-V</i> characteristics can be dramatically enhanced owing to the carrier doping by TTF adsorption.

Charge and spin interplay in a molecular-dimer-based organic Mott insulator

Triangular lattice quasi-two-dimensional Mott insulators based on the bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) molecule and its analogies present a possibility to produce exotic phases by coupling charge and spin degrees of freedom. In this work we discuss magnetic properties of one such material, $\ensuremath{\kappa}$-(BEDT-${\mathrm{TTF})}_{2}\mathrm{Hg}{(\mathrm{SCN})}_{2}\mathrm{Cl}$, which is found at the border of the phase transition between a Mott insulator into a charge ordered state. Our magnetic susceptibility and cantilever magnetization measurements demonstrate how the charge degree of freedom defines magnetic properties for few different charge phases observed in this material as a function of temperature. Between ${T}_{\text{CO}}=30\phantom{\rule{0.16em}{0ex}}\text{K}$ and ${T}_{\text{S}}=24\phantom{\rule{0.16em}{0ex}}\text{K}$ we observe charge and spin separation due to one-dimensional charge stripes formed in this material below ${T}_{\text{CO}}=30\phantom{\rule{0.16em}{0ex}}\text{K}$. Below ${T}_{\text{S}}=24\phantom{\rule{0.16em}{0ex}}\text{K}$ charge and spin degrees of freedom demonstrate coupling. Spin-singlet correlations develop below 24 K, however, the melting of charge order below 15 K prevents the spin-singlet-state formation, leaving the system in the inhomogeneous state with charge ordered spin-singlet domains and charge and spin fluctuating ones.

Theoretical Study of Solvent Effects on the Electronic and Thermodynamic Properties of Tetrathiafulvalene (TTF) Molecule Based on DFT

Tetrathiafulvalene () is an organosulfur compound used in the production of molecular devices such as switches, sensors, nonlinear optical devices and rectifiers. In this work, a theoretical study on the effects of solvent on TTF molecule was investigated and reported based on Density Functional Theory (DFT) as implemented in Gaussian 03 package using B3LYP/6-31++G(d,p) basis set. Different solvents were introduced as a bridge to investigate their effects on the electronic structure. The HUMO, LUMO, energy gap, global chemical index, thermodynamic properties, NLO and DOS analysis of the TTF molecule in order to determine the reactivity and stability of the molecule were obtained. The results obtained showed that the solvents have effects on the electronic and non-linear-optical properties of the molecule. The optimized bond length revealed that the molecule has strong bond in gas phase with smallest bond length of about 1.0834Å than in the rest of the solvents. It was observed that the molecule is more stable in acetonitrile with HOMO-LUMO gap and chemical hardness of 3.6373eV and 1.8187eV respectively. This indicates that the energy gap and chemical hardness of TTF molecule increases with the increase in polarity and dielectric constant of the solvents. The computed results agreed with the results in the literature. The thermodynamics and NLO properties calculation also indicated that TTF molecule has highest value of specific heat capacity (Cv), total dipole moment () and first order hyperpolarizability () in acetonitrile, while acetone has the highest value of entropy and toluene has a slightly higher value of zero point vibrational energy (ZPVE) than the rest of the solvents. The results show that careful selection of the solvents and basis sets can tune the frontier molecular orbital energy gap of the molecule and can be used for molecular device applications.

Theoretical Study for Chemical Reactivity Descriptors of Tetrathiafulvalene in gas phase and solvent phases based on Density Functional Theory

The aim of the study is to investigate the effects of solvent polarity on the frontier molecular orbitals energy gap and global chemical reactivity of Tetrathiafulvalene in order to understand the stability and reactivity of Tetrathiafulvalene in a different solvent medium. Density functional theory with (B3LYP/6-311++G) basis set was used to perform a variety of calculations in both the gas and solvent phases. Besides dipole moment, Mulliken charge distribution, and thermodynamic properties were calculated in five solvent phases namely (water, acetone, Tetrahydrofuran (THF), Carbon tetrachloride (CCl4), and benzene). The calculations were carried out using the Gaussian 09 software, and the results showed that the solvents have an effect on the optimized parameters. Moreover, Mulliken population analysis, and local reactivity as Fukui Functions (FFs) from the natural bond orbitals (NBO) charges are computed to understand the electrophile, nucleophile region, and chemical activity of the title molecule. The dipole moment in gas phase and solvent medium is 0.00 Debye. Also, it was observed that the global chemical reactivity parameters change depending on the molecular structure and polarity of the solvents. Tetrathiafulvalene molecule was observed to have greater stability (low reactivity) in the water solvent with an EHOMO-ELUMO energy gap of 3.946 eV while it has higher reactivity (low stability) in the gas phase with EHOMO-ELUMO energy gap of 3.872eV. finally, this result indicates that Tetrathiafulvalene is an excellent candidate for future studies of semiconductor and optoelectronic materials.

Strategies for Controlling Through-Space Charge Transport in Metal-Organic Frameworks via Structural Modifications.

In recent years, charge transport in metal-organic frameworks (MOFs) has shifted into the focus of scientific research. In this context, systems with efficient through-space charge transport pathways resulting from π-stacked conjugated linkers are of particular interest. In the current manuscript, we use density functional theory-based simulations to provide a detailed understanding of such MOFs, which, in the present case, are derived from the prototypical Zn2(TTFTB) system (with TTFTB4− corresponding to tetrathiafulvalene tetrabenzoate). In particular, we show that factors such as the relative arrangement of neighboring linkers and the details of the structural conformations of the individual building blocks have a profound impact on bandwidths and charge transfer. Considering the helical stacking of individual tetrathiafulvalene (TTF) molecules around a screw axis as the dominant symmetry element in Zn2(TTFTB)-derived materials, the focus, here, is primarily on the impact of the relative rotation of neighboring molecules. Not unexpectedly, changing the stacking distance in the helix also plays a distinct role, especially for structures which display large electronic couplings to start with. The presented results provide guidelines for achieving structures with improved electronic couplings. It is, however, also shown that structural defects (especially missing linkers) provide major obstacles to charge transport in the studied, essentially one-dimensional systems. This suggests that especially the sample quality is a decisive factor for ensuring efficient through-space charge transport in MOFs comprising stacked π-systems.

Multistep Electron Injection Dynamics and Optical Nonlinearity Investigations of π-Extended Thioalkyl-Substituted Tetrathiafulvalene Sensitizers

A comprehensive investigation is presented on the photophysical and third-order nonlinear optical (NLO) properties of two thioalkyl-substituted tetrathiafulvalene molecules (referred here as G1 and G3) to understand their utility as photosensitizers for dye-sensitized solar cell (DSSC) and optoelectronic applications. Both steady-state and time-resolved (in the fs–ns time regime) absorption and photoluminescence (PL) spectroscopy techniques were employed to comprehend the excited-state properties of the molecules in solution as well as in thin films deposited on both quartz and mesoporous TiO2 layers. The spectroscopy measurements in solution and thin films deposited on quartz provided the excited-state properties of dye molecules. Time-resolved PL measurements at the dye–TiO2 interface provided initial evidence of electron injection by fast PL quenching decay dynamics for both the molecules. Detailed target analysis of the femtosecond transient absorption spectroscopy (TAS) data of the dye–TiO2 sample revealed a multistep ultrafast electron injection for both molecules with the fastest injection component being 374 and 314 fs for G1 and G3 molecules, respectively. The ultrafast NLO properties of G1 and G3 were studied using the Z-scan technique with 800 nm, ∼70 fs laser pulses. The open aperture measurements showed three-photon absorption with magnitudes of coefficients 4.7 × 10–5 cm3/GW2 and 5.2 × 10–5 cm3/GW2, and the closed aperture measurements provided second hyperpolarizability (γ) values of 3.5 × 10–31 esu and 4.2 × 10–31 esu for G1 and G3, respectively. Additionally, the onset of optical limiting was estimated to be 5.8 × 10–3 J/cm2 and 5.7 × 10–3 J/cm2 for G1 and G3 molecules, respectively.

A molecular device providing a remarkable spin filtering effect due to the central molecular stretch caused by lateral zigzag graphene nanoribbon electrodes.

Through the density functional theory, we studied molecular devices composed of single tetrathiafulvalene (TTF) molecules connected with zigzag graphene nanoribbon electrodes by four different junctions. Interestingly, some devices have exhibited half-metallic behavior and can bring out a perfect spin filtering effect and remarkable negative differential resistance behavior. The current-voltage characteristics show that these four devices possess different spin current values. We found that all the TTF molecules were stretched due to interactions with the electrodes in the four devices. This leads to the Fermi levels of the three devices being down-shifted to the valence band; therefore, these devices exhibit half-metallic properties. The underlying mechanisms of the different spin current values are attributed to the different electron transmission pathways (via chemical bonds or through hopping between atoms). These results suggest that the device properties and conductance are controlled by different junctions. Our work predicts an effective way for designing high-performance spin-injected molecular devices.

An effective approach to realize graphene based p-n junctions via adsorption of donor and acceptor molecules

Atomically thin two dimensional materials such as graphene offer excellent capabilities suitable for a number of low power versatile applications. Here, employing first principle calculations, we introduce a feasible approach to realize an efficient graphene based p-n junction (PNJ) which is composed of non-covalently physisorbed tetracyanoquinodimethane (TCNQ) and tetrathiafulvalene (TTF) molecules onto an armchair graphene nanoribbon (AGNR). We show that compared to conventional graphene based p-n systems, our suggested PNJ exhibits low threshold voltage (Vth), large current-voltage ratio, and almost no sensitivity to conformational variations. Using a simple model, we also provide a theoretical background to explain the rectifying behavior of the suggested PNJ and show that tuning the distance between p and n doped regions modifies the current-voltage ratio. Our study indicates that the perfect diode behavior along with stability under various practical conditions makes our proposed PNJ a promising building block to fabricate next generation graphene based nanosize transistors.

Edge functionalization of finite graphene nanoribbon superlattices

The effect of chemical functionalization on the electronic properties of graphene nanoribbon superlattices with zigzag and armchair terminations is investigated using the density functional theory. The calculated positive binding energies imply that all the considered structures are stable before and after chemical modifications. The superlattices with armchair edges are characterized by a wide energy gap while those with zigzag edges have a narrow energy gap. The energy gap in superlattices with armchair edges nearly independent of their length while it strongly decreases and almost closes in superlattices with zigzag edges. The energy gap is comparably sensitive to the width variations in both types of the superlattices. It was found that the electric dipole moment increases with increasing the width in the case of armchair while it oscillates in zigzag superlattices. The electric dipole moment can be enhanced by chemical functionalization with COOH and NH2 groups. The effect of this functionalization is moderate for the energy gap, but the adsorption of tetracyanoquinodimethane transforms the system from insulator (Eg = 2.66 eV) to a narrow band gap semiconductor (Eg = 0.25 eV). The adsorption energy of tetracyanoquinodimethane and tetrathiafulvalene molecules can be enhanced by chemical functionalization which makes graphene superlattices useful for sensor applications and wastewater treatment.

Study of stacking interactions between two neutral tetrathiafulvalene molecules in Cambridge Structural Database crystal structures and by quantum chemical calculations.

Tetrathiafulvalene (TTF) and its derivatives are very well known as electron donors with widespread use in the field of organic conductors and superconductors. Stacking interactions between two neutral TTF fragments were studied by analysing data from Cambridge Structural Database crystal structures and by quantum chemical calculations. Analysis of the contacts found in crystal structures shows high occurrence of parallel displaced orientations of TTF molecules. In the majority of the contacts, two TTF molecules are displaced along their longer C2 axis. The most frequent geometry has the strongest TTF-TTF stacking interaction, with CCSD(T)/CBS energy of -9.96 kcal mol-1. All the other frequent geometries in crystal structures are similar to geometries of the minima on the calculated potential energy surface.

Exceptional Optical Absorption of Buckled Arsenene Covering a Broad Spectral Range by Molecular Doping.

Using density functional theory calculations, we demonstrate that the electronic and optical properties of a buckled arsenene monolayer can be tuned by molecular doping. Effective p-type doping of arsenene can be realized by adsorption of tetracyanoethylene and tetracyanoquinodimethane (TCNQ) molecules, while n-doped arsenene can be obtained by adsorption of tetrathiafulvalene molecules. Moreover, owing to the charge redistribution, a dipole moment is formed between each organic molecule and arsenene, and this dipole moment can significantly tune the work function of arsenene to values within a wide range of 3.99–5.57 eV. Adsorption of TCNQ molecules on pristine arsenene can significantly improve the latter’s optical absorption in a broad (visible to near-infrared) spectral range. According to the AM 1.5 solar spectrum, two-fold enhancement is attained in the efficiency of solar-energy utilization, which can lead to great opportunities for the use of TCNQ–arsenene in renewable energy. Our work clearly demonstrates the key role of molecular doping in the application of arsenene in electronic and optoelectronic components, renewable energy, and laser protection.

Supramolecular conducting microfibers from amphiphilic tetrathiafulvalene-based organogelator

An amphiphilic tetrathiafulvalene molecule was designed and readily synthesized. The am-TTF can gelate a variety of organic solvents in view of multiple intermolecular interactions, especially in polar solvent. SEM observation provided clear evidence for the self-assembled micro/nanofibers morphologies in gelation state. Moreover, XRD measurements indicated the formation of highly-ordered columnar structures. The FT-IR spectra revealed that the formation of mixed-valence states with the absorption over 1700 cm−1, showing the semiconductive behaviors with the conductivity of 10−4 S/cm. The am-TTF based conducting fibers could be promising candidates for organic electronics.

Tuning Optoelectronic and Chiroptic Properties of Peptide-Based Materials by Controlling the Pathway Complexity.

Supramolecular chemistry has evolved from the traditional focus on thermodynamic on-pathways to the complex study of kinetic off-pathways, which are strongly dependent on environmental conditions. Moreover, the control over pathway complexity allows nanostructures to be obtained that are inaccessible through spontaneous thermodynamic processes. Herein, we present a family of peptide-based π-extended tetrathiafulvalene (exTTF) molecules that show two self-assembly pathways leading to two distinct J-aggregates, namely metastable (M) and thermodynamic (T), with different spectroscopic, chiroptical, and electrochemical behavior. Moreover, cryo-transmission electron microscopy (cryo-TEM) reveals a different morphology for both aggregates and a direct observation of the morphological transformations from tapes to twisted ribbons.

Anderson-Type Polyoxometalates Functionalized by Tetrathiafulvalene Groups: Synthesis, Electrochemical Studies, and NLO Properties.

Three polyoxometalates (POMs) functionalized by tetrathiafulvalene (TTF) molecules have been synthesized by a coupling reaction between the Anderson-type POMs [MnMo6O18{(OCH2)3CNH2}2]3- or [AlMo6O18(OH)3{(OCH2)3CNH2}]3- and the TTF carboxylic acid derivative (MeS)3TTF(S-CH2-CO2H). The monofunctionalized TTF-AlMo6 POM contains one TTF group covalently grafted on an Al Anderson platform. The symmetrical TTF-MnMo6-TTF POM possesses two TTF groups grafted on each side of a Mn Anderson derivative while the asymmetrical TTF-MnMo6-SP POM contains a TTF and a spiropyran groups. These three trianionic species have been characterized by elemental analysis, 1H and 13C NMR, FT-IR spectroscopy, ESI-MS spectrometry, and single-crystal X-ray diffraction (for TTF-MnMo6-TTF). In the solid state, the grafted TTF molecules of TTF-MnMo6-TTF POMs interact via S···S and π···π interactions and form chains. The electrochemical properties of the complexes reflect the contributions of both the inorganic POM and the TTF moieties. Despite adsorption of the oxidized hybrid species on the Pt grid working electrode, UV-vis-NIR spectroelectrochemical investigations evidence peaks characteristic of the oxidation of the TTF units. Finally, hyper-Rayleigh scattering (HRS) measurements show that the three novel TTF derivatives exhibit β values between 20 and 37 × 10-30 esu. Moreover it is observed that the oxidation of the TTF moieties by Fe3+ ions increases the NLO response. These values are in the order of magnitude of that found for the well-known 4-dimethylamino- N-methyl-4-stilbazolium (DAS+) cation (β = 60 × 10-30 esu).

Functional supramolecular tetrathiafulvalene-based films with mixed valences states

Abstract Tetrathiafulvalene molecules substituted with a carboxylic acid group (TTFCOOH) were bound as redox-active moieties into a poly(4-vinyl pyridine) (P4VP) skeleton through non-covalent interactions (hydrogen bonds). The aspect of the resulting P4VP-TTFCOOH films showed a uniform and smooth morphology. Moreover, the redox function of TTFCOOH in P4VP-TTFCOOH was demonstrated using tetrachloroauric acid, iron(III) perchlorate and iodine vapors as doping agents. The oxidized states of TTFCOOH as well as the mixed valance state TTFCOOH 0 -TTFCOOH +• were generated in a controlled manner in solid state, resulting in an organic film capable of charge transport. The charge transport along the organic donor molecules hydrogen bonded to the polymer matrix was demonstrated employing Electrostatic Force Microscopy (EFM).

Photophysical properties of charge transfer pairs encapsulated inside macrocycle cage: A density functional theory study

Density functional theory calculations have been performed on three charge transfer donor–acceptor (D–A) molecular pairs, i.e. naphthalene-diamine (Naph) and tetrathiafulvalene (TTF) molecules as electron donors and benzene-diimide (Diimide) and tetracyanoquinodimethane (TCNQ) as electron acceptors. Structural, charge transfer and optical properties of the systems have been studied. The D–A pairs then has been considered inside a macrocycle (cucurbit[8]uril) cavity and Naph–Diimide and TTF–Diimide pairs have been shown to exhibit changes in their structures and orientations, TTF–TCNQ pair does not show any significant structural change. Our work suggests that these changes in structures or orientations are result of electronic repulsion between the keto group oxygen atoms and it can lead to tuning of charge transfer and optical properties of the systems.

Adsorption of tetrathiafulvalene (TTF) on Cu(1 0 0): can π-stacked 1-D aggregates be formed at low temperature?

We present a combined experimental and theoretical study that shows the formation of one-dimensional aggregates of tetrathiafulvalene (TTF) molecules along high symmetry directions of the Cu(100) metal surface at low temperatures. Our first principles calculations permit to explain the observations. We find an adsorption geometry of the molecules in a tilted configuration that is explained as the result of a delicate balance between intermolecular and molecule–surface attractive forces of comparable strength. The inclusion of van der Waals (vdW) forces in the description is instrumental to arrive at this conclusion.

Molecular electronic states in charge transfer complex studied by x-ray absorption spectroscopy

The electronic states of tetrathiafulvalene (TTF: TTF = C6H4S4) molecule in organic ferroelectric TTF-p-bromanil (TTF-BA: BA = C6Br4O2) and TTF crystals have been investigated by x-ray absorption spectroscopy (XAS) measurement at S K-edge. We elucidated that the peak structure at 2470.5 eV directly reflects the existence of hole in the highest occupied molecular orbital (HOMO) state of the TTF molecule in TTF-BA; that is consistent with the ionic TTF molecule (TTF+). The XAS of TTF-BA was evaluated on the basis of first-principles calculations, and the calculated spectra reproduce well the shape of experimental spectrum and the peak energy of the HOMO state.