Two Tetrathiafulvalene Research Articles

Boron-bridged bis(tetrathiafulvalene) zwitterionic neutral radical conductors: substituent effects on intramolecular and intermolecular electronic interactions and physical properties

Abstract We have recently proposed a new molecular design for neutral radical molecular conductors, based on the chemical composition of D2X-type charge-transfer salts (D = π-electron donor molecule, X = monovalent anion). Namely, we connected two tetrathiafulvalene (TTF)-based π-electron skeletons having a charge of +0.5 via a boron anion B–, to obtain a purely organic zwitterionic neutral radical {[(PDT-TTF-Cat)2]+B–}• that shows unique electronic states and properties in the crystal due to the intramolecular and intermolecular interactions of the +0.5-charged π-skeletons. In order to further explore the structural and electronic features of this kind of zwitterionic neutral radical conductor, in this study, we have examined chemical modifications to {[(PDT-TTF-Cat)2]+B–}•. As a result, an analog molecule {[(BMT-TTF-Cat)2]+B–}•, in which propylenedithio (PDT) groups on the TTF terminals in {[(PDT-TTF-Cat)2]+B–}• are replaced by bis(methylthio) ones, was successfully synthesized as air-stable single crystals. Interestingly, this chemical modification causes intramolecular charge disproportionation between the two TTF-based π-skeletons (i.e. the monovalent cation radical TTF+• and the neutral TTF0) coupled to the modulation of the intermolecular distances and interactions between these π-skeletons, leading to electrical and magnetic properties significantly different from those of the crystal of {[(PDT-TTF-Cat)2]+B–}•.

Programming Tetrathiafulvalene‐Based Covalent Organic Frameworks for Promoted Photoinduced Molecular Oxygen Activation

AbstractDespite the pivotal role of molecular oxygen (O2) activation in artificial photosynthesis, the activation efficiency is often restricted by sluggish exciton dissociation and charge transfer kinetics within polymer photocatalysts. Herein, we propose two tetrathiafulvalene (TTF)‐based imine‐linked covalent organic frameworks (COFs) with tailored donor‐acceptor (D–A) structures, TTF‐PDI‐COF and TTF‐TFPP‐COF, to promote O2 activation. Because of enhanced electron push‐pull interactions that facilitated charge separation and transfer behavior, TTF‐PDI‐COF exhibited superior photocatalytic activity in electron‐induced O2 activation reactions over TTF‐TFPP‐COF under visible light irradiation, including the photosynthesis of (E)‐3‐amino‐2‐thiocyano‐α,β‐unsaturated compounds and H2O2. These findings highlight the significant potential of the rational design of COFs with D–A configurations as suitable candidates for advanced photocatalytic applications.

Photoinduced asymmetric charge trapping in a symmetric tetraazapyrene-fused bis(tetrathiafulvalene) conjugate.

In fused donor-acceptor (D-A) ensembles, rapid charge recombination often occurs because the D and A units are spatially close and strongly coupled. To the best of our knowledge, a long-lived charge separated (CS) state is still elusive in such systems. The results presented here show that symmetric annulation of two tetrathiafulvalene (TTF) donors to a central tetraazapyrene (TAP) acceptor via two quinoxaline units leads to a CS state lifetime of a few ns. A detailed study of the electronic interactions between TTF and TAP units in the ground and excited states was performed and compared with the asymmetric counterpart by cyclic voltammetry, optical absorption and ultrafast transient absorption spectroscopy. The results demonstrate that the photoinduced asymmetric charge trapping between two TTFs significantly stabilizes the CS state, which is also verified theoretically.

Redox-Driven Folding, Unfolding, and Refolding of Bis(tetrathiafulvalene) Molecular Switch.

We report redox-driven folding, unfolding, and refolding motions of a synthetic molecular system, in which two tetrathiafulvalene (TTF) units are tethered onto a conformationally rigid yet torsionally flexible π-conjugated backbone. Upon one-electron oxidation, this molecular switch undergoes swiveling motions from a fully relaxed and freely rotating Z-shaped conformation to a compact folded conformation stabilizing π-stacked radical species. Subsequent one-electron oxidation produces dicationic intermediates, which either engage in intimate π-π interactions or transition to an open structure. Further oxidation, however, brings the molecule back to the initial conformation to minimize the repulsion between doubly-charged TTF units. Intriguingly, the reaction coordinates of this redox-driven structural change have strong dependence on the environment, such as the solvent (THF vs CH2Cl2) and supporting electrolyte (PF6- vs B(C6F5)4-). With a proper design, factors that are typically considered as "secondary effects" could dictate the solution dynamics and reaction pathways of structural folding and unfolding, all driven by controlled delivery of electrons.

Interactions between tetrathiafulvalene units in dimeric structures - the influence of cyclic cores.

A selection of cyclic and acyclic acetylenic scaffolds bearing two tetrathiafulvalene (TTF) units was prepared by different metal-catalyzed coupling reactions. The bridge separating the two TTF units was systematically changed from linearly conjugated ethyne, butadiyne and tetraethynylethene (trans-substituted) units to a cross-conjugated tetraethynylethene unit, placed in either acyclic or cyclic arrangements. The cyclic structures correspond to so-called radiaannulenes having both endo- and exocyclic double bonds. Interactions between two redox-active TTF units in these molecules were investigated by cyclic voltammetry, UV–vis–NIR and EPR absorption spectroscopical methods of the electrochemically generated oxidized species. The electron-accepting properties of the acetylenic cores were also investigated electrochemically.

Slow Magnetic Relaxation in a Redox‐Active Tetrathiafulvalene‐Based Ferromagnetic Dysprosium Complex

AbstractThe association of the two 4,5‐bis(thiomethyl)‐4′‐carboxytetrathiafulvalene (HL1) and 4,5‐bis(thiomethyl)‐4′‐(2‐pyridyl‐N‐oxide)carbamoyltetrathiafulvalene (L2) with the metalloprecursor [Dy(tta)3]·2H2O (tta = 2‐thenoyltrifluoroacetonate) leads to the formation of the dinuclear complex of formula [Dy(tta)2(L1)(L2)]2·2CH2Cl2. Static magnetic measurements highlight significant ferromagnetic interactions between the DyIII ions, and dynamic magnetic measurements demonstrate single‐molecule‐magnet behaviour with an energy barrier of 20 cm–1 and a relaxation time of 8.6(9) × 10–6 s. The thermal dependence of the magnetic susceptibility was evaluated by using a crystal field approach (Stevens operators), which confirmed the Ising character of the system. Finally, electrochemistry shows a complex multiredox system with the successive oxidations of the two tetrathiafulvalene (TTF) ligands.

Tetrathiafulvalene‐Based Macrocycles Formed by Radical Cation Dimerization: The Role of Intramolecular Hydrogen Bonding and Solvent

Compounds 1 a and 1 b were prepared by appending two tetrathiafulvalene (TTF) units to an aromatic amide segment that is driven by six or two intramolecular N-H⋅⋅⋅O hydrogen bonds to adopt a folded conformation. UV/Vis absorption experiments revealed that if the TTF units were oxidized to TTF(·+) radical cations, the two compounds could form a stable single molecular noncovalent macrocycle in less polar dichloromethane or dichloroethane or a bimolecular noncovalent macrocycle in a binary mixture of dichloromethane with a more polar solvent owing to remarkably enhanced dimerization of the TTF(·+) units. The stability of the (TTF(·+))2 dimer was evaluated through UV/Vis absorption, electron paramagnetic resonance, and cyclic voltammetry experiments and also by comparing the results with those of control compound 2. The results showed that introduction of the intramolecular hydrogen bonds played a crucial role in promoting the stability of the (TTF(·+))2 dimer and thus the noncovalent macrocyclization of the two backbones in both uni- and bimolecular manners.

Tetrathiafulvalene‐Based Mixed‐Valence Acceptor–Donor–Acceptor Triads: A Joint Theoretical and Experimental Approach

This work presents a joint theoretical and experimental characterisation of the structural and electronic properties of two tetrathiafulvalene (TTF)-based acceptor-donor-acceptor triads (BQ-TTF-BQ and BTCNQ-TTF-BTCNQ; BQ is naphthoquinone and BTCNQ is benzotetracyano-p-quinodimethane) in their neutral and reduced states. The study is performed with the use of electrochemical, electron paramagnetic resonance (EPR), and UV/Vis/NIR spectroelectrochemical techniques guided by quantum-chemical calculations. Emphasis is placed on the mixed-valence properties of both triads in their radical anion states. The electrochemical and EPR results reveal that both BQ-TTF-BQ and BTCNQ-TTF-BTCNQ triads in their radical anion states behave as class-II mixed-valence compounds with significant electronic communication between the acceptor moieties. Density functional theory calculations (BLYP35/cc-pVTZ), taking into account the solvent effects, predict charge-localised species (BQ(.-)-TTF-BQ and BTCNQ(.-)-TTF-BTCNQ) as the most stable structures for the radical anion states of both triads. A stronger localisation is found both experimentally and theoretically for the BTCNQ-TTF-BTCNQ anion, in accordance with the more electron-withdrawing character of the BTCNQ acceptor. CASSCF/CASPT2 calculations suggest that the low-energy, broad absorption bands observed experimentally for the BQ-TTF-BQ and BTCNQ-TTF-BTCNQ radical anions are associated with the intervalence charge transfer (IV-CT) electronic transition and two nearby donor-to-acceptor CT excitations. The study highlights the molecular efficiency of the electron-donor TTF unit as a molecular wire connecting two acceptor redox centres.

Iron(II) Complexes Based on π‐Conjugated Terpyridine Ligands with Tetrathiafulvalene or Its Radical Analogue

Two tetrathiafulvalene (TTF) functionalized 2,2′:6′,2″-terpyridine derivatives, 4′-tetrathiafulvalene-2,2′:6′,2″-terpyridine (L1) and 6,6″-dimethyl-4′-tetrathiafulvalene-2,2′:6′,2″-terpyridine (L2), were synthesized and characterized. Based on L1 and L2, four electrochemically active TTF-containing iron(II) complexes, [FeII(L1)2][ClO4]2 (1), [FeII(L1·+)2][ClO4]4 (2), [FeII(L1)2][CF3SO3]2 (3) and [FeII(L2)2][ClO4]2 (4), were successfully obtained. The preparation, spectroscopic and electrochemical properties of these new compounds as well as the crystal structures of complexes 1, 3 and 4 are described. Magnetic studies on 4 (with the ligand L2) suggest that the FeII ion is in the high-spin state. Complex 2 was isolated as an interesting and stable open-shell substance, and the free spin is mainly associated with the TTF radicals, as indicated by EPR, UV/Vis spectra, electrochemical analysis, spectroelectrochemical measurements and XPS spectra. After the oxidation and the formation of the radical cation, the electrical conductivity of 2 is almost 3 orders of magnitude higher than that of 1. DFT and TDDFT calculations provided insight into interpreting the electronic properties of complex 1 and its oxidized states.

Quantum chemical calculations and experimental studies of third-order nonlinear optical properties of conjugated TTF–quinones

To investigate microscopic third-order nonlinear optical (NLO) behaviour of two tetrathiafulvalene (TTF) derivatives, TTF–diquinone triad (1) and TTF–monoquinone dyad (2), we have computed both dispersion-free and also dispersion of dipole polarizabilities (α) and third-order hyperpolarizabilities (γ) at 532nm wavelength using time-dependent Hartree–Fock (TDHF) method. The one-photon absorption (OPA) characterizations of the title molecules have been theoretically obtained by means of configuration interaction (CI) method with all doubly occupied molecular orbitals. We have also calculated the dynamic third-order susceptibilities (χ(3)) using the TDHF method. Our theoretical results on the maximum OPA wavelengths, third-order susceptibilities and corresponding microscopic NLO responses are in good agreement with the previous experimental observations of the examined TTF-based molecules. The highest occupied molecular orbitals (HOMO), the lowest unoccupied molecular orbitals (LUMO) and the HOMO–LUMO band gaps for 1 and 2 have been evaluated by density functional theory (DFT) quantum mechanical calculations at B3LYP/6–31G(d,p) level.

A Tetrathiafulvalene‐Functionalized Radiaannulene with Multiple Redox States

Multiple states: Fusing a central expanded radiaannulene (RA) core with two tetrathiafulvalene (TTF) units furnishes a molecule that can exist in several redox states with characteristic UV/Vis/IR absorptions. The radical cation was found to be of mixed valence (MV) character as reflected by a low-energy intervalence transition.

Tetrathiafulvalene hydrazone an efficient precursor of various chelating electroactive ligands

Novel bidentate electroactive ligands containing one or two tetrathiafulvalene (TTF) cores as redox active unit have been synthesized thanks to the condensation of various carbonyl derivatives with TTF hydrazone. The electron donating ability of these redox active ligands determined by cyclic voltammetry is described together with the investigations of their molecular structures by X-ray diffraction studies. The chelating ability of these ligands has been exemplified through the coordination to molybdenum carbonyl fragment or the complexation to difluoroboron moiety.

Mechanically Stabilized Tetrathiafulvalene Radical Dimers

Two donor-acceptor [3]catenanes-composed of a tetracationic molecular square, cyclobis(paraquat-4,4'-biphenylene), as the π-electron deficient ring and either two tetrathiafulvalene (TTF) and 1,5-dioxynaphthalene (DNP) containing macrocycles or two TTF-butadiyne-containing macrocycles as the π-electron rich components-have been investigated in order to study their ability to form TTF radical dimers. It has been proven that the mechanically interlocked nature of the [3]catenanes facilitates the formation of the TTF radical dimers under redox control, allowing an investigation to be performed on these intermolecular interactions in a so-called "molecular flask" under ambient conditions in considerable detail. In addition, it has also been shown that the stability of the TTF radical-cation dimers can be tuned by varying the secondary binding motifs in the [3]catenanes. By replacing the DNP station with a butadiyne group, the distribution of the TTF radical-cation dimer can be changed from 60% to 100%. These findings have been established by several techniques including cyclic voltammetry, spectroelectrochemistry and UV-vis-NIR and EPR spectroscopies, as well as with X-ray diffraction analysis which has provided a range of solid-state crystal structures. The experimental data are also supported by high-level DFT calculations. The results contribute significantly to our fundamental understanding of the interactions within the TTF radical dimers.

Vesicle Self-Assembly by Tetrathiafulvalene Derivatives in Both Polar and Nonpolar Solvents and Pseudo-Rotaxane Mediated Vesicle-to-Microtube Transformation

This paper reports the self-assemblies of vesicles from two tetrathiafulvalene (TTF) derivatives (T1 and T2), that bear four or two amphiphilic side chains, in both polar and nonpolar solvents. The formation of vesicles is evidenced by scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), and dynamic light scattering (DLS) experiments, while the microstructural aspects of the vesicles are investigated by UV-vis, (1)H NMR, and high resolution TEM, which support a monolayer model for the vesicles. It is revealed that the formation of vesicles is driven by the combination of multiple noncovalent interactions, including pi-pi stacking, hydrogen-bonding, van der Waals force, and S...S interactions. It is also found that, in the presence of electron-deficient cyclobis(paraquat-p-phenylene) tetracation cyclophane, vesicles of T2 can transform into microtubes as a result of the formation of the pseudo[2]rotaxane between the TTF unit of T2 and the cyclophane. This process can be reversed by introducing pristine TTF into the solution of microtubes, due to release of T2 from the pseudo[2]rotaxane through the formation of a more stable complex between pristine TTF and tetracation cyclophane.

Nonlinear conductivity with an extremely small threshold electric field in the organic conductor(TSM−TTP)(I3)5∕3

$(\mathrm{TSM}\text{\ensuremath{-}}\mathrm{TTP}){({\mathrm{I}}_{3})}_{5∕3}$ is a $1∕6$-filled one-dimensional system composed of an extended donor molecule which has two tetrathiafulvalene (TTF) units in a molecule, where TSM-TTP is 2,5-bis[4,5-bis(methylseleno)-1,3-dithiol-2-ylidene]-1,3,4,6-tetrathiapentalene. Nonlinear conductivity is observed in the insulating state below $20\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, and the metallic state is restored above a very small threshold electric field of $0.3\phantom{\rule{0.3em}{0ex}}\mathrm{V}∕\mathrm{cm}$ at $4.2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The extremely sensitive nonlinearity is ascribed to the inhomogeneous insulating state generated by the weak and disordered anion potentials on the otherwise highly conducting intramolecular charge order state in the double-TTF molecule.

Synthesis, optical spectroscopy and electrochemistry of TTF-derived metallophthalocyanine complexes

Two tetrathiafulvalene (TTF)-derived metallophthalocyanine complexes were synthesized. The structures of the target compounds and their intermediates have been characterized by NMR, MS, EA, UV–VIS and mp. The results of cyclic voltammetry indicated that the presence of zinc or magnesium phthalocyanine slightly affected the first oxidation of 4,5-ethylenedithiotetrathiafulvalene (EDT-TTF) unit. The EDT-TTF unit on the peripheral sites of the zinc phthalocyanine core could be more easily oxidized than the one on the same sites of the magnesium phthalocyanine core.

Molecular shuttles based on tetrathiafulvalene units and 1,5-dioxynaphthalene ring systems.

Six different degenerate [2]rotaxanes were synthesized and characterized. The rotaxanes contained either two tetrathiafulvalene (TTF) units or two 1,5-dioxynaphthalene (DNP) ring systems, both of which serve as recognition sites for a cyclobis(paraquat-p-phenylene) (CBPQT4+) ring. Three different spacer units were incorporated into the dumbbell components of the [2]rotaxanes between the recognition sites. They include a polyether chain, a terphenyl unit, and a diphenyl ether linker, all of which were investigated in order to probe the effect of the spacers on the rate of the shuttling process. Data from dynamic 1H NMR spectroscopy revealed a relatively small difference in the DeltaG++ values for the shuttling process in the [2]rotaxanes containing the three different spacers, in contrast to a large difference between the TTF-containing rotaxanes (18 kcal mol(-1)) and the DNP-containing rotaxanes (15 kcal mol(-1)). This 3 kcal mol(-1) difference is predominantly a result of a ground-state effect, reflecting the much stronger binding of TTF units to the CBPQT4+ ring in comparison with DNP ring systems. An examination of the enthalpic (DeltaH++) and entropic (DeltaS++) components for the shuttling process in the DNP-containing rotaxanes revealed significant differences between the three spacers, a property which could be important in designing new molecules for incorporation into molecular electronic and nanoelectromechanical (NEMs) devices.

Facile Syntheses of 4-(2-Cyanoethylthio)-1,3-dithiole-2-thione and New Electron­ Donors with Two TTF Units and Compounds with Bis(1,3-dithiole-2-thione) Groups

The synthetic conditions for the preparation of 4-(2-cyanoethylthio)-1,3-dithiole-2-thione (1) from TBA2·[Zn(dmit)2] were studied. Compound 1 was used to synthesize new electron donors with two tetrathiafulvalene (TTF) units. Other interesting compounds that are good precursors for tetrathiafulvalenophanes were also easily prepared from TBA2·[Zn(dmit)2].

Tetrathiafulvalene-containing pseudorotaxanes formed between dibenzylammonium salts and crown ethers

The synthesis of two tetrathiafulvalene (TTF) derivatives, one carrying arms incorporating four dibenzylammonium centers and the other encompassing two annulated crown ether rings—i.e., hydrogen bond donor and acceptor functions, respectively, is described. In the presence of macrocyclic polyethers—e.g., DB24C8 and BPP34C10—and dibenzylammonium hexafluorophosphate, these two TTF derivatives form pseudorotaxanes as evidenced by 1H NMR spectroscopy, mass spectrometry, and differential pulse voltammetry.

A unique molecular donor containing two tetrathiafulvalene (TTF) units fused to 1,4 - ditellurin: Synthesis, X-ray structure and cyclic voltammetry

A new molecular donor composed of two TTF moieties fused to 1,4-ditellurin ( 3) has been synthesized and the structure has been characterized by X-ray diffraction. The cyclic voltammetry of both 3 and its methyl analogue 4 display two reversible two-electron oxidation waves.