Tetrathiafulvalene Derivatives Research Articles

Hierarchical Modeling of the Nonlinear Optical Response of Composite Materials Based on Tetrathiafulvalene Derivatives

The presented work concerns computational investigations of the physical properties of composite materials based on polymer matrix and nonlinear optical (NLO) active chromophores. The structural, electronic, and optical properties of selected tetrathiafulvalene (TTF)-based chromophores have been calculated using quantum chemical methods. The polymer matrix changes the physical properties of the inserted chromophores influencing their optical parameters. To explain the mechanism of the NLO signal occurrence from the composites based on poly(methyl methacrylate) (PMMA) matrix and TTF chromophores, their structures are modeled using the classical molecular dynamics. In consequence, the structural properties of the composites are discussed according to the NLO requirements. By developing the theoretical model based on a discrete multipole local field approach, the impact of polymer matrix on the optical properties of chromophores is explained.

High-Voltage Catholyte for High-Energy-Density Nonaqueous Redox Flow Battery.

Redox flow batteries (RFBs) with high energy densities are essential for efficient and sustainable long-term energy storage on a grid scale. To advance the development of nonaqueous RFBs with high energy densities, a new organic RFB system employing a molecularly engineered tetrathiafulvalene derivative ((PEG3/PerF)-TTF) as a high energy density catholyte was developed.When paired with a lithium metal anode, the two-electron-active (PEG3/PerF)-TTF catholyte produced a cell voltage of 3.56 V for the first reduction and 3.92 V for the second reduction process. In cyclic voltammetry and flow cell tests, the redox chemistry exhibited excellent cycling stability. The Li|(PEG3/PerF)-TTF batteries, with concentrations of 0.1 M and 0.5 M, demonstrated capacity retention rates of ~94% (99.87% per cycle, 97.52% per day) and 90% (99.93% per cycle, 99.16% per day), and the average Coulombic efficiencies of 99.38% and 98.35%, respectively. The flow cell achieved a high power density of 129 mW/cm2. Furthermore, owing to the high redox potential and solubility of (PEG3/PerF)-TTF, the flow cell attained a high operational energy density of 72 Wh/L (100 Wh/L theoretical). A 0.75 M flow cell exhibited an even higher operational energy density of 96 Wh/L (150 Wh/L theoretical).

Enhancing Intramolecular Ferromagnetic Coupling in Tetrathiafulvalene-Nitronyl Nitroxide-Based Compounds through Spin Polarization Mechanism.

Spin-polarized donor radicals based on tetrathiafulvalene (TTF) derivatives and nitronyl nitroxide (NN) radicals in which one-electron oxidation involves the HOMO instead of the SOMO are well known for exhibiting magnetoresistance. In particular, BTBN consists of one dibromo-TTF and one NN radical, which are linked by a phenyl coupler group. One of the key factors driving magnetoresistance is the presence of intramolecular ferromagnetic (FM) coupling between the oxidized π-donor (TTF+⋅, D unit) and NN (R unit). Here, a theoretical study is carried out to assess suitable candidates with enhanced FM coupling with respect BTBN, which is thus used as a reference. The study is conducted via in silico chemical modification of the substituents of the BTBN basic functional units (D and R radicals, C coupler) to benefit from the spin polarization mechanism to boost the intramolecular FM coupling, aiming to distort the BTBN radical arrangement within the molecular crystal as little as possible, in the event the material can be synthesized. NICSiso(1) and Wiberg's Bond Order are analyzed to further assist in identifying promising potential candidates, since the decrease in aromaticity is expected to enhance the diradical character and give rise to a larger magnetic coupling value. The most favorable diradical building block to replace the BTBN moiety results from using a hydroxyl-ethylene (-(H)C=C(OH)-) as a coupler preserving BTBN original radicals, namely, NN and TTF+⋅ units. This study aims at illustrating the feasibility of improving the intramolecular FM interaction between radical moieties, which is fully realized, as a first step towards the synthesis of new materials with (possibly) enhanced magnetoresistance properties.

Synthesis, Structures, Electrochemical and Optical Properties of Vinyl‐Extended Tetrathiafulvalene Derivatives Functionalized with Two 2,6‐Dicyano‐λ5‐Phosphinine Units

AbstractDerivatives of vinyl‐extended tetrathiafulvalene (TTF) functionalized with two 2,6‐dicyano‐λ5‐phosphinine units (3 a–c) have been successfully synthesized. Cyclic voltammograms of all the derivatives are composed of three pairs of redox waves. The first and second redox waves correspond to one‐electron transfer processes, in which the extended TTF moiety participated predominantly. The third redox wave corresponded to a two‐electron transfer process, in which the two 2,6‐dicyano‐λ5‐phosphinine units were involved. The redox potentials at which the tetracations of 3 a–c were generated were considerably more negative than expected, probably due to the formation of stable closed‐shell structures by conjugation between 2,6‐dicyano‐λ5‐phosphinine units. X‐ray structural analyses of 3 b, 3 c, and (3b2+)(Sb2Cl82−)(C6H5OCH3) revealed that the vinyl‐extended TTF moiety in all the compounds adopts an almost planar structure, while the phosphinine units are significantly rotated relative to the extended TTF plane. The fluorescence spectroscopy revealed that the emission intensity of 3 b was very small in both the neutral and oxidized states.

Theoretical Study of the Global Reactivity and Theoretical Characterization of the Preferential Sites of Reactivity of Five Derivatives of Tetrathiafulvalene

Theoretical Study of the Global Reactivity and Theoretical Characterization of the Preferential Sites of Reactivity of Five Derivatives of Tetrathiafulvalene

Dual Optimization of Interface Defects and Hole Transporting Layers with Tetrathiafulvalene Derivatives for Antimony Selenosulfide Solar Cells

Modification of hole transporting layers (HTLs) to reduce the interface defects is an important strategy to promote hole extraction and suppress charge recombination for Sb2(S,Se)3 (antimony selenosulfide) solar cells. Herein, a simple doping method with the tetrathiafulvalene derivatives (MeS‐TTF and Cyano‐TTF) is developed to reduce the dangling bonding defects on the surface of Sb2(S,Se)3 films and improve the photovoltaic performances of Sb2(S,Se)3 solar cells. The studies show that the tetrathiafulvalene derivatives can effectively passivate the ionic defects through the chelation mechanism with Sb atoms and suppress the nonradiative recombination. Meanwhile, the MeS‐TTF dopant can also enhance the hole mobility of HTLs and improve the hole transport. The results indicate that the MeS‐TTF can achieve the dual function of interface defect passivation and hole mobility improvement. As a result of the dual‐function dopant, a significant increase in efficiency from 7.73% to 8.45% can be obtained. The outcomes of this study highlight that this dual‐function doping strategy is an effective method to passivate the interface defects and enhance the hole mobility for the excellent photovoltaic performances of Sb2(S,Se)3 solar cells.

Synthesis of 2-(Methylthio)-1,3-dithioles from 1,3-Dithiole-2-thiones: Important Building Blocks in Tetrathiafulvalene Chemistry.

2-(Methylthio)-1,3-dithioles are important heterocyclic compounds used for the preparation of redox-active derivatives of tetrathiafulvalene as they serve as precursors for phosphonate esters that can be employed in Horner-Wadsworth-Emmons olefination reactions. Here, we present a mild and less hazardous method than previous methods for converting readily accessible 1,3-dithiole-2-thiones into 2-(methylthio)-1,3-dithioles by methylation with trimethyl orthoformate and HBF4·Et2O and a subsequent reduction with NaBH4.

Unimolecular Chiral Stepping Inversion Machine.

Intelligent molecular machines that are driven by light, electricity, and temperature have attracted considerable interest in the fields of chemistry, materials, and biology. Herein, a unimolecular chiral stepping inversion molecular machine (SIMM) was constructed by a coupling reaction between dibromo pillar[5]arene and a tetrathiafulvalene (TTF) derivative (PT3 and PT5). Compared with the longer aliphatic linker PT5, PT3 with a shorter aliphatic linker shows chiral stepping inversion, achieving chiral inversion under a two-electron redox potential. Benefiting from the successive reversible two-electron redox potential of TTF, the self-exclusion and self-inclusion conformational transformations of SIMM can proceed in two steps under redox, leading to the chirality step inversion in the pillar[5]arene core. Electrochemical experiments and circular dichroism (CD) spectra show that the redox processes can cause SIMM CD signaling to reversibly switch. More importantly, as the oxidant Fe(ClO4)3 was increased from 0.1 to 1 equiv, the CD spectral signal of SIMM disappeared at 1 equiv, and further addition of Fe(ClO4)3 resulted in the CD signal reversed from positive to negative at 309 nm, indicating that the chirality was reversed after chemical oxidation and reached a negative maximum with the addition of 2 equiv Fe(ClO4)3; thus, redox-triggered chiral stepping inversion was achieved. Furthermore, the chiral inversion can be restored to its original state after the addition of 2 equiv of reducing agent, sodium ascorbate. This work demonstrates unimolecular chiral stepping inversion, providing a new perspective on stimulus-responsive chirality in molecular machines.

Chiral Crystals, Jack, Conductivity and Magnetism

AbstractRecently, the application of magnetic fields to chiral chemical systems has been rewarding. In a forward‐looking 1986 paper, ‘Chiral Metals?’, Wallis, Karrer, and Jack D. Dunitz forecast ‘that the limitation to proper symmetry elements in a chiral conductor could be associated with the emergence of new properties, those connected with interactions between applied electric and magnetic fields and their internal counterparts.’ This was a prescient remark, but it has become manifest in ways that would not have been foreseen in its details by the authors. Here are reviewed the development of chiral conductors broadly imagined by Dunitz and coworkers, based on enantiopure tetrathiafulvalene derivatives that restrict space groups to those that have only symmetry operations of the first kind, as well as the new emergent properties associated with the transport of electrons when magnetic fields are applied to chiral crystals among other systems. These include electrical magnetochiral anisotropy (eMChA), inverse electrical magnetochiral anisotropy (ieMChA), helimagnetism and chirality induced spin selectivity (CISS). The conclusion discussing the circumstances under which achiral TTF crystals becomes chiral, only seems to introduce an oxymoron.

Electron Storage Performance of Metal–Organic Frameworks Based on Tetrathiafulvalene–Tetrabenzoate as Cathode Active Materials in Lithium- and Sodium-Ion Batteries

Tetrathiafulvalene (TTF) derivatives are well-known molecular-based conductors. They are used to prepare porous crystalline structures with efficient charge transport properties and suitable chemical design, such as metal–organic frameworks (MOFs), covalent organic frameworks (COFs), and hydrogen-bonded organic frameworks (HOFs). MOFs based on TTF derivatives have attracted attention as electrode-active materials for rechargeable metal-ion batteries owing to multielectron redox reactions, resulting in improved battery capacity. This study focuses on TTF–tetrabenzoate (H4TTFTB), which exhibits good redox and mechanical properties as the ligand of MOFs. We evaluated the battery performance using MOFs based on H4TTFTB with three types of core metals ([M2(TTFTB)], where M = Zn, Co, and Mn) as cathode active materials for rechargeable lithium-ion and sodium-ion batteries (LIBs and SIBs). The cycle stability and battery capacity at high current densities were improved by MOF formation in both LIBs and SIBs, indicating that MOF formation has the potential to achieve improved charging/discharging rates. In addition, the battery capacities and cycle stability of SIBs were larger than those of LIBs for all materials. These results demonstrate the interesting battery performance of MOFs based on H4TTFTB as cathode active materials for LIBs and SIBs. This implies that the application of redox-active and rigid H4TTFTB as the ligand of MOFs is an effective method for realizing high-performance energy storage devices. These findings can contribute to an improved design of cathode active materials for high-performance rechargeable metal-ion batteries for sustainable energy storage.

Chalcogen bonding and variable charge transfer degree in two polymorphs of 1 : 1 conducting salts with segregated stacks

Harnessing a bis(selenomethyl)tetrathiafulvalene derivative as a donor, two polymorphs of conducting 1 : 1 charge transfer salts are realized thanks to original packing structures supported by chalcogen bonding interactions.

Tetrathiafulvalene (TTF) derivatives as catholytes for dual-type redox flow batteries: molecular engineering enables high energy density and cyclability

Redox flow batteries (RFBs) have received increasing attention on large-scale energy storage owing to their ability to decouple energy and power.

A tetrathiafulvalene salt of the nitrite (NO2−) anion: investigations of the spin-Peierls phase

The first nitrite salt of a tetrathiafulvalene derivative exhibits a rare chessboard-like organization of the conducting stacks, with a spin-Peierls transition at 70 K.

Electrochemistry of Tetrathiafulvalene Ligands Assembled on the Surface of Gold Nanoparticles

The synthesis of a tetrathiafulvalene (TTF) derivative, S-[4-({4-[(2,2'-bi-1,3-dithiol-4-ylmethoxy)methyl] phenyl}ethynyl)phenyl] ethanethioate, suitable for the modification of gold nanoparticles (AuNPs), is described in this article. The TTF ligand was self-assembled on the AuNP surface through ligand exchange, starting from dodecanethiol-stabilized AuNPs. The resulting modified AuNPs were characterized by TEM, UV-Vis spectroscopy, and electrochemistry. The most suitable electrochemical method was the phase-sensitive AC voltammetry at very low frequencies of the sine-wave perturbation. The results indicate a diminishing electronic communication between the two equivalent redox centers of TTF and also intermolecular donor-acceptor interactions manifested by an additional oxidation wave upon attachment of the ligand to AuNPs.

Molecular Diodes With Tunable Threshold Voltage Based on π‐Extended Tetrathiafulvalene

AbstractIt is a challenge to control the threshold voltage (defined as the voltage at which the current density increases sharply in the direction of forward bias), one of the basic parameters that define a molecular diode. The problem is that strong Fermi‐level pinning of molecular frontier orbitals and the changes in the electronic structure are often overshadowed by the changes in the supramolecular structure. A chemical control approach is proposed to shift the effective threshold voltage of a series of molecular diodes composed of self‐assembled monolayers (SAMs) of π‐extended tetrathiafulvalene (exTTF) derivatives. The highest occupied molecular orbital of the molecules can be tuned by ≈0.6 eV (maximum) with the minimum changes in the supramolecular structure of the SAMs by introducing chlorine atoms or amino substitutional groups into the exTTF moieties. To the best of the authors’ knowledge, this is the first paper that reports that the threshold voltage of the exTTF‐based diode can be modulated from 0.65 to 1.70 V. In addition, it is shown that these four molecular diodes can operate as half‐wave rectifiers with the threshold voltage at positive direct current output ranging from 1.63 to 2.40 V, with the input voltage being 3.0 V at 500 Hz.

Tetrathiafulvalene Derivatives as Hole-Transporting Materials in Perovskite Solar Cell.

Over a couple of decades perovskite solar cells have become a highly promising photovoltaic technology. Choosing a dopant-free Hole-Transporting Material (HTM) that offers protection to a perovskite layer from oxidation is one of the viable strategies while addressing the stability of perovskite solar cell. In this line of interest, tetrathiafulvale (TTF) derivatives have shown promise in the past. However, studies that focus on small-molecule TTF derivatives as potential HTM options are scarce. The present study is an attempt to explore the applicability of a few TTF derivatives as HTM in a perovskite solar cell. Here four TTF derivatives, namely, TTF-1 (experimentally reported in a previous study), TTF-2, DBTTF1, and TMTSF1, were studied through electronic structure calculations. The properties concerning HTM, such as impact of adsorption on molecular structure, absorption spectra, distribution of frontier molecular orbitals, interaction energy between TTF derivative and MAPbI3 surface, and charge transfer at an interface, were analyzed. Results show that TTF-2 has the expected energy-level alignment, transparency in the visible range of solar spectrum, and good charge-injection ability at the interface with a perovskite layer. Hence, TTF-2 could be a potential hole-transporting material for a perovskite solar cell, and it can perform better than TTF-1.

Enhanced Photocatalytic Hydrogen Production Activity by Constructing a Robust Organic-Inorganic Hybrid Material Based Fulvalene and TiO2.

A novel redox-active organic-inorganic hybrid material (denoted as H4TTFTB-TiO2) based on tetrathiafulvalene derivatives and titanium dioxide with a micro/mesoporous nanomaterial structure has been synthesized via a facile sol-gel method. In this study, tetrathiafulvalene-3,4,5,6-tetrakis(4-benzoic acid) (H4TTFTB) is an ideal electron-rich organic material and has been introduced into TiO2 for promoting photocatalytic H2 production under visible light irradiation. Notably, the optimized composites demonstrate remarkably enhanced photocatalytic H2 evolution performance with a maximum H2 evolution rate of 1452 μmol g−1 h−1, which is much higher than the prototypical counterparts, the common dye-sensitized sample (denoted as H4TTFTB-5.0/TiO2) (390.8 μmol g−1 h−1) and pure TiO2 (18.87 μmol g−1 h−1). Moreover, the composites perform with excellent stability even after being used for seven time cycles. A series of characterizations of the morphological structure, the photoelectric physics performance and the photocatalytic activity of the hybrid reveal that the donor-acceptor structural H4TTFTB and TiO2 have been combined robustly by covalent titanium ester during the synthesis process, which improves the stability of the hybrid nanomaterials, extends visible-light adsorption range and stimulates the separation of photogenerated charges. This work provides new insight for regulating precisely the structure of the fulvalene-based composite at the molecule level and enhances our in-depth fundamental understanding of the photocatalytic mechanism.

Semiconductor Porous Hydrogen-Bonded Organic Frameworks Based on Tetrathiafulvalene Derivatives.

Herein, we report on the use of tetrathiavulvalene-tetrabenzoic acid, H4TTFTB, to engender semiconductivity in porous hydrogen-bonded organic frameworks (HOFs). By tuning the synthetic conditions, three different polymorphs have been obtained, denoted MUV-20a, MUV-20b, and MUV-21, all of them presenting open structures (22, 15, and 27%, respectively) and suitable TTF stacking for efficient orbital overlap. Whereas MUV-21 collapses during the activation process, MUV-20a and MUV-20b offer high stability evacuation, with a CO2 sorption capacity of 1.91 and 1.71 mmol g–1, respectively, at 10 °C and 6 bar. Interestingly, both MUV-20a and MUV-20b present a zwitterionic character with a positively charged TTF core and a negatively charged carboxylate group. First-principles calculations predict the emergence of remarkable charge transport by means of a through-space hopping mechanism fostered by an efficient TTF π–π stacking and the spontaneous formation of persistent charge carriers in the form of radical TTF•+ units. Transport measurements confirm the efficient charge transport in zwitterionic MUV-20a and MUV-20b with no need for postsynthetic treatment (e.g., electrochemical oxidation or doping), demonstrating the semiconductor nature of these HOFs with record experimental conductivities of 6.07 × 10–7 (MUV-20a) and 1.35 × 10–6 S cm–1 (MUV-20b).

Organic Molecular Conductors Based on Tetramethyl-TTP: Structural and Electrical Properties Modulated by the Anion Size and Shape.

The tetramethyl derivative of bis-fused tetrathiafulvalene, 2,5-bis(4,5-dimethyl-1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene (TMTTP), has been successfully synthesized. Most of the radical cation salts consisting of TMTTP feature a high electrical conductivity of σrt = 101 to 102 S cm-1 on a single crystal. The anion shape and size of TMTTP conductors modulate the electrical properties. The PF6- and AsF6- salts exhibit metallic conductivity down to 10 K, while the ReO4- and AuI2- salts show metal-to-insulator (MI) transition at 126 and 11 K, respectively. Single-crystal X-ray structure analysis of (TMTTP)2X (X = PF6, AsF6, BF4, and ReO4) and (TMTTP)3AuI2 reveals that the donor packing motif is categorized as the so-called β-type. The tight-binding band calculations of (TMTTP)2X (X = ReO4, BF4, PF6, and AsF6) suggest these salts are characterized by quasi-one-dimensional Fermi surfaces. The band calculation based on X-ray structure analysis of (TMTTP)2ReO4 at 100 K demonstrates that the MI transition of this salt is associated with the charge ordering with the zigzag stripe pattern.

Interfacial Reduction Nucleation of Noble Metal Nanodots on Redox-Active Metal-Organic Frameworks for High-Efficiency Electrocatalytic Conversion of Nitrate to Ammonia.

Electrochemically converting nitrate to ammonia is a promising route to realize artificial nitrogen recycling. However, developing highly efficient electrocatalysts is an ongoing challenge. Herein, we report the construction of stable and redox-active zirconium metal-organic frameworks (Zr-MOFs) based on Zr6 nanoclusters and redox-reversible tetrathiafulvalene (TTF) derivatives as inorganic nodes and organic linkers, respectively. The redox-active Zr-MOF can facilitate the in situ reduction of noble metal precursors free of external reductants and realize the uniform nucleation of noble metal nanodots (NDs) on Zr-MOF, achieving the preparation of M-NDs/Zr-MOF (M = Pd, Ag, or Au). The highly porous Zr-MOF with good conductivity can facilitate the mass transfer process. Among the M-NDs/Zr-MOF catalysts, Pd-NDs/Zr-MOF exhibits the highest electrocatalytic activity, delivering a NH3 yield of 287.31 mmol·h-1·g-1cat. and a Faradaic efficiency of 58.1%. The proposed interfacial reduction nucleation strategy for anchoring M NDs on Zr-MOFs can be applied to other challenging energy conversion reactions.