Tetrathiafulvalene Donors Research Articles

Design and Synthesis of Aviram-Ratner-Type Dyads and Rectification Studies in Langmuir-Blodgett (LB) Films.

The design and synthesis of Aviram-Ratner-type molecular rectifiers, featuring an anilino-substituted extended tetracyanoquinodimethane (exTCNQ) acceptor, covalently linked by the σ-spacer bicyclo[2.2.2]octane (BCO) to a tetrathiafulvalene (TTF) donor moiety, are described. The rigid BCO spacer keeps the TTF donor and exTCNQ acceptor moieties apart, as demonstrated by X-ray analysis. The photophysical properties of the TTF-BCO-exTCNQ dyads were investigated by UV/Vis and EPR spectroscopy, electrochemical studies, and theoretical calculations. Langmuir-Blodgett films were prepared and used in the fabrication and electrical studies of junction devices. One dyad showed the asymmetric current-voltage (I-V) curve characteristic for rectification, unlike control compounds containing the TTF unit but not the exTCNQ moiety or comprising the exTCNQ acceptor moiety but lacking the donor TTF part, which both gave symmetric I-V curves. The direction of the observed rectification indicated that the preferred electron current flows from the exTCNQ acceptor to the TTF donor.

Electronic and magnetic properties of TTF and TCNQ covered Co thin films

Interfacial effects like orbital hybridization and charge transfer strongly influence the transfer of spins from ferromagnetic metals to organic semiconductors and can lead to the formation of interfacial states with distinct magnetic properties. The changes in the electronic and magnetic properties of a thin Co film upon adsorption of a layer of either the molecular organic electron donor tetrathiafulvalene (TTF) or the acceptor tetracyanoquinodimethane (TCNQ) have been investigated by X-ray absorption spectroscopy and X-ray magnetic circular dichroism using synchrotron radiation. Clear differences between the spectra of the adsorbed molecules and the neutral molecules show the hybridization of the molecular orbitals with the Co interface. Deposition of both organic materials leads to a small increase of the ratio of the orbital magnetic moment to the spin magnetic moment of the Co atoms at the interface. The main effect of overlayer deposition is a modification of the magnetic hysteresis of the Co film: The TCNQ slightly reduces the coercivity of the Co, while the TTF increases the coercivity by a factor of ∼1.5. These complementary effects of either a molecular organic electron donor or acceptor on the interfacial properties of a metal ferromagnetic thin film are a promising result for the controlled modification of the magnetic structure of hybrid interfaces.

Electron Transfer Pathways in a Tetrathiafulvalene-Aluminum(III) Porphyrin-Free-Base Porphyrin Triad Studied Using Electron Spin Polarization

The electron transfer pathways in two axially bound triads based on aluminum(III) porphyrin (AlPor) are investigated using the electron spin polarization patterns of the final radical pair state. In the triads, TTF-(Ph)n-py-AlPor-Ph-H2Por (n = 0, 1), free-base porphyrin (H2Por) is attached covalently to the Al(III) center, while the donor tetrathiafulvalene (TTF) coordinates to Al(III) via an appended pyridine on the opposite face of the porphyrin ring. Excitation of the triad at 532 nm leads to absorption by both AlPor and H2Por and to two possible charge separation pathways. In the liquid crystalline solvent 5CB, spin polarized transient electron paramagnetic resonance spectra of a weakly coupled radical pair are observed and assigned to the state \({\text{TTF}}^{ \cdot+ } {\text{H}}_{2} {\text{Por}}^{ \cdot- }\). The radical pair spectra are analyzed using a structural model of the complex to determine the dipolar coupling and relative orientation of the radicals. The inertia tensor calculated from the structural model is used to derive the principal values and axes of the order matrix. It is shown that the observed polarization pattern is only consistent with ferromagnetic exchange coupling in the radical pair. The spectra can be reproduced as the sum of two contributions originating in electron transfer from the excited singlet state of AlPor and from the excited the triplet state of H2Por. The latter is shown to account for the integral emissive net polarization observed in the spectra.

Synthesis of Novel Extended Tetrathiafulvalene Donors for OFETs

Synthesis of Novel Extended Tetrathiafulvalene Donors for OFETs

Charge‐Transfer Salts Based on a Dissymmetrical Cyano‐Substituted Tetrathiafulvalene Donor

AbstractThree salts of the dissymmetrical TTF derivative cyanobenzene‐ethylenedithio‐tetrathiafulvalene (CNB‐EDT‐TTF) with different anions, namely, (CNB‐EDT‐TTF)2[M(mnt)2] [M = Ni (1), Au (2); mnt = maleonitriledithiolate] and (CNB‐EDT‐TTF)FeBr4 (3) were prepared and characterized by single‐crystal X‐ray diffraction, magnetic susceptibility, and electrical conductivity measurements. Compounds 1 and 2 are isostructural with a crystal structure characterized by segregated chains of side‐by‐side donor dimers and acceptors, and compound 3 presents donors in dimerized stacks. In spite of the different structural types and stoichiometries, all of these compounds have C–N···H pairing interactions associated with R22(10) synthons between donors in nearby chains. All compounds are poor semiconductors, and the magnetic susceptibility of 1 is dominated by the contribution of the paramagnetic [Ni(mnt)2] anions with small antiferromagnetic interactions. The magnetic susceptibility of 3 is dominated by the paramagnetic FeBr4 anions and follows a Curie–Weiss law with a Weiss temperature θ = –19 K, which denotes significant antiferromagnetic interactions that are most likely mediated by the donors.

Vilsmeier–Haack Type Formylation on 6-Aryl-1,4-dithiafulvenes and Syntheses of Novel Extended Tetrathiafulvalene Donors

The Vilsmeier–Haack type formylations on various 6-aryl-1,4-dithiafulvenes were examined. The furyl derivatives on treatment with an excess of POCl3 in DMF at room temperature mainly afforded dialdehydes substituted at the 6-position and the furan ring, while the thienyl derivatives and the phenyl derivatives mainly gave monoformylated derivatives substituted at the 6-position. The obtained mono- and dialdehydes were converted into monoaryl-substituted 2,2′-ethanediylidene-bis(1,3-dithiole) derivatives and heteroaromatic ring-inserted [3]dendralene derivatives with triple 1,3-dithiol-2-ylidenes and their TTF-fused analogues. Electrochemical properties of the new π-electron donors were also investigated by cyclic voltammetry.

Enantiopure Radical Cation Salt Based on Tetramethyl-Bis(ethylenedithio)-Tetrathiafulvalene and Hexanuclear Rhenium Cluster

Electrocrystallization of the (S,S,S,S) enantiomer of tetramethyl-bis(ethylenedithio)-tetrathiafulvalene donor 1 in the presence of the dianionic hexanuclear rhenium (III) cluster [Re6S6Cl8]2− affords a crystalline radical cation salt formulated as [(S)-1]2·Re6S6Cl8, in which the methyl substituents of the donors adopt an unprecedented all-axial conformation. A complex set of intermolecular TTF···TTF and cluster···TTF interactions sustain an original tridimensional architecture.

Tuning thermoelectric properties of graphene/boron nitride heterostructures

Using density functional theory combined with a Green’s function scattering approach, we examine the thermoelectric properties of hetero-nanoribbons formed from alternating lengths of graphene and boron nitride. In such structures, the boron nitride acts as a tunnel barrier, which weakly couples states in the graphene, to form mini-bands. In un-doped nanoribbons, the mini bands are symmetrically positioned relative to the Fermi energy and do not enhance thermoelectric performance significantly. In contrast, when the ribbons are doped by electron donating or electron accepting adsorbates, the thermopower S and electronic figure of merit are enhanced and either positive or negative thermopowers can be obtained. In the most favourable case, doping with the electron donor tetrathiafulvalene increases the room-temperature thermopower to −284 μv K−1 and doping by the electron acceptor tetracyanoethylene increases S to 210 μv K−1. After including both electron and phonon contributions to the thermal conductance, figures of merit ZT up to of order 0.9 are obtained.

Structural, Magnetic and DFT studies on a Charge-Transfer Salt of a Tetrathiafulvalenepyridyl-(1,5-diisopropyl) verdazyl Diradical Cation.

A new tetrathiafulvalene (TTF) donor covalently appended with a 1,5-diisopropylverdazyl radical through a cross-conjugated pyridyl linker (3) has been prepared and characterised. Reaction of 3 with tetracyanoquinonedimethane (TCNQ) afforded the 2:1 charge-transfer complex (3)2 ⋅TCNQ (4), in which the IR and structural data are consistent with 0.25 e- charge transfer from the TTF donor (D) to the TCNQ acceptor (A). The TTF and TCNQ molecules adopt a mixed-stack D⋅⋅⋅D⋅⋅⋅A arrangement that does not facilitate conduction. A solution EPR spectrum of 4 comprises a broad featureless singlet, which is consistent with the presence of a TCNQ radical anion. Theoretical studies were performed to probe the exchange interactions within selected fragments of 4 with and without charge transfer. In the absence of charge transfer, DFT calculations reveal weak antiferromagnetic exchange between verdazyl radicals within the (3)2 monoradical unit. However, partial oxidation of the dimer (3)2 to the diradical cation leads to an S= ground state, in which the verdazyl radical spins are now aligned co-parallel as a consequence of antiferromagnetic exchange to the additional delocalised TTF-based spin containing unit. The magnetic properties of 4 are consistent with a net S= spin state per formula unit with dominant antiferromagnetic interactions between spin-bearing building blocks.

Exploring the Electronic Structure of an Organic Semiconductor Based on a Compactly Fused Electron Donor–Acceptor Molecule

A Mott-type semiconductor based on a compactly fused and partially oxidized electron donor-acceptor (D-A) molecule was recently prepared and identified to exhibit a large room-temperature conductivity of 2 S cm(-1) . In a marked contrast to the organic conductors characterized by relatively well decoupled and segregated uniform stacks of D and A moieties, the formally half-oxidized tetrathiafulvalene donors of the actual compound are organized in columnar π stacks only, whereby the coplanar electron-acceptor units, namely benzothiadiazole, are closely annulated along their ridges. Herein, we present a theoretical study that explores the electronic structure of this novel type of organic semiconductor. The highly symmetric-solid state material behaves as a one-dimensional electronic system with strong antiferromagnetic interactions (coupling constant>200 cm(-1) ). The unique shape and local dipole of this redox-active fused electron D-A molecule lays the basis for further investigations of the collective electronic structure, mainly in the function of different counterions embedded in the crystalline lattice.

A structural investigation of novel thiophene-functionalized BEDT-TTF donors for application as organic field-effect transistors

Three new unsymmetrical thiophene-functionalized bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) donors (1–3) have been synthesized, characterised and examined as semiconducting materials for organic field-effect transistor (OFET) devices. The X-ray crystal structures of (1) and (2) reveal both neutral donors pack as dimers with lateral S⋯S contacts. For (1) the molecules are co-facially stacked in a head-to-tail manner with some degree of latitudinal slippage. A device prepared from a crystalline thin film of (1) deposited on unmodified silicon wafer substrate displays a mobility of 5.9 × 10−3 cm2 V−1 s−1 with an on/off ratio of 11. The shorter CH2 linker in (2) results in poorer orbital overlap, likely due to significant longitudinal and latitudinal slippage between molecules in the crystal lattice. As a consequence, no field-effect response was observed for the device fabricated from (2).

Gold Metal Liquid-Like Droplets

Simple methods to self-assemble coatings and films encompassing nanoparticles are highly desirable in many practical scenarios, yet scarcely any examples of simple, robust approaches to coat macroscopic droplets with continuous, thick (multilayer), reflective and stable liquid nanoparticle films exist. Here, we introduce a facile and rapid one-step route to form films of reflective liquid-like gold that encase macroscopic droplets, and we denote these as gold metal liquid-like droplets (MeLLDs). The present approach takes advantage of the inherent self-assembly of gold nanoparticles at liquid-liquid interfaces and the increase in rates of nanoparticle aggregate trapping at the interface during emulsification. The ease of displacement of the stabilizing citrate ligands by appropriate redox active molecules that act as a lubricating molecular glue is key. Specifically, the heterogeneous interaction of citrate stabilized aqueous gold nanoparticles with the lipophilic electron donor tetrathiafulvalene under emulsified conditions produces gold MeLLDs. This methodology relies exclusively on electrochemical reactions, i.e., the oxidation of tetrathiafulvalene to its radical cation by the gold nanoparticle, and electrostatic interactions between the radical cation and nanoparticles. The gold MeLLDs are reversibly deformable upon compression and decompression and kinetically stable for extended periods of time in excess of a year.

A tetrathiafulvalene (TTF)-conjugated microporous polymer network.

Conjugated microporous polymer networks have been prepared from the strong electron donor tetrathiafulvalene (TTF) and 1,3,5-triethynylbenzene (TEB) by using the Sonogashira-Hagihara cross-coupling reaction. Optimization of reaction conditions yields polymers with surface areas of up to 434 m(2) g(-1) . The strong electron-donating properties of the network can be proven by iodine exposure. Structural and electronic changes due to formation of the charge-transfer salt from TTFs in the porous network and iodine within the pores are investigated.

ChemInform Abstract: Intramolecular Electron Transfer and Charge Delocalization in Bistable Donor‐Acceptor Systems Based on Perchlorotriphenylmethyl Radicals Linked to Ferrocene and Tetrathiafulvalene Units

A comparative analysis of the physicochemical properties of different donor–acceptor dyads, based on a perchlorotriphenylmethyl radical acceptor subunit linked through a vinylene π-bridge to ferrocene derivatives (1–3) or a tetrathiafulvalene (4) donor subunit, is presented. Intramolecular electron transfer and charge delocalization of these donor–acceptor dyads are discussed on the basis of data obtained in solution by cyclic voltammetry, UV–Vis near-infrared, and electron spin resonance spectroscopies. Bistability in the crystalline phase is also discussed on the basis of the results provided by X-ray diffraction analysis and temperature-dependent Mossbauer spectra. Copyright © 2014 John Wiley & Sons, Ltd.

Electron-Rich Arene–Ruthenium Metalla-architectures Incorporating Tetrapyridyl–Tetrathiafulvene Donor Moieties

A series of arene ruthenium architectures have been prepared from coordination-driven self-assembly using dinuclear p-cymene ruthenium acceptors and π-donating tetratopic tetrapyridyl–tetrathiafulvalene donor ligands. The synthetic strategy, based on a geometric interaction approach, leads to four electroactive metalla-assemblies, 1–4 (one molecular cube and three metallaplates), that were characterized by NMR, ESI-MS, X-ray diffraction, and cyclic voltammetry. Rationalization of their formation discrepancy was completed by DFT calculations supported by structural features of their constituting TTF and Ru-complex components. Metalla-architectures possessing electron-rich cores (3, cis-4, and trans-4) interact strongly with picric acid (PA) to yield cocrystallized products, PA + metalla-assemblies, confirmed by single-crystal X-ray structure analyses.

Intramolecular electron transfer and charge delocalization in bistable donor–acceptor systems based on perchlorotriphenylmethyl radicals linked to ferrocene and tetrathiafulvalene units

A comparative analysis of the physicochemical properties of different donor–acceptor dyads, based on a perchlorotriphenylmethyl radical acceptor subunit linked through a vinylene π‐bridge to ferrocene derivatives (1–3) or a tetrathiafulvalene (4) donor subunit, is presented. Intramolecular electron transfer and charge delocalization of these donor–acceptor dyads are discussed on the basis of data obtained in solution by cyclic voltammetry, UV–Vis near‐infrared, and electron spin resonance spectroscopies. Bistability in the crystalline phase is also discussed on the basis of the results provided by X‐ray diffraction analysis and temperature‐dependent Mössbauer spectra. Copyright © 2014 John Wiley & Sons, Ltd.

Chemical Reactivity of Electron-Doped and Hole-Doped Graphene

The chemical reactivity of electron-doped and hole-doped graphene was studied by means of first principles calculations, on the basis of dispersion corrected density functional theory. To model hole-doped graphene, the widely known electron acceptor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) was utilized, while the electron donor tetrathiafulvalene (TTF) was selected for the electron-doped case. The results demonstrate that the reactivity of graphene can be modified by the adsorption of electron donating/withdrawing molecules. The reactions considered were the addition of fluorine atoms and hydroxyl radicals. In both cases, it was observed that the adsorption of F4-TCNQ and TTF increased the reactivity of graphene. This outcome was expected for electron-doped graphene because we have recently shown that lithium increases the reactivity of graphene. Yet, for F4-TCNQ, the finding is surprising given that this molecule accepts 0.4 e– from graphene. The gas phase free energies of associati...

Light-Induced Spin Polarization in Porphyrin-Based Donor–Acceptor Dyads and Triads

The light-induced spin polarization generated by sequential electron transfer in an axially bound triad based on Al(III) porphyrin (AlPor) is discussed. In the triad, $$\text {TTF} \!-\! \text {Ph} \!-\! \text {py}\!\to\!\text {AlPor}\! - \!\text {Ph}\! -\! \text {NDI}$$ , the electron acceptor naphthalene diimide (NDI) is attached covalently to the Al(III) center, while the donor tetrathiafulvalene (TTF) coordinates to Al(III) via an appended pyridine (py) on the opposite face of the porphyrin ring. Excitation of the porphyrin at room temperature in solution leads to charge separation between the donor and acceptor. In the liquid crystalline solvent 5CB, a spin-polarized transient electron paramagnetic resonance spectrum of a weakly coupled radical pair is observed and is assigned to the state $$ \text{TTF}^{\cdot + } \text{NDI}^{\cdot - } $$ . In the absence of the donor, a spectrum of the triplet state of the strongly coupled radical pair $$ \text{AlPor}^{ \cdot + } \text{NDI}^{ \cdot - } $$ is obtained. The analysis of the spectra is described using a model developed by Kandrashkin et al. (Appl Magn Reson 15: 417–447, 1998). It is shown that in the triad the spectrum of $$ \text {TTF}^{ \cdot + } \text {NDI}^{ \cdot - } $$ shows evidence of the singlet–triplet mixing in the precursor $$ \text{AlPor}^{ \cdot + } \text{NDI}^{ \cdot - } $$ . At later time, singlet recombination leads to inversion of the spectrum, from which the singlet back reaction lifetime is estimated as 350 ns. The decay of the inverted spectrum yields a lifetime of 8.3 μs for the triplet back reaction lifetime.

Tuning the Electronic Properties of Nonplanar exTTF-Based Push–Pull Chromophores by Aryl Substitution

A new family of π-extended tetrathiafulvalene (exTTF) donor-acceptor chromophores has been synthesized by [2 + 2] cycloaddition of TCNE with exTTF-substituted alkynes and subsequent cycloreversion. X-ray data and theoretical calculations, performed at the B3LYP/6-31G** level, show that the new chromophores exhibit highly distorted nonplanar molecular structures with largely twisted 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) units. The electronic and optical properties, investigated by UV/vis spectroscopy and electrochemical measurements, are significantly modified when the TCBD acceptor unit is substituted with a donor phenyl group, which increases the twisting of the TCBD units and reduces the conjugation between the two dicyanovinyl subunits. The introduction of phenyl substituents hampers the oxidation and reduction processes and, at the same time, largely increases the optical band gap. An effective electronic communication between the donor and acceptor units, although limited by the distorted molecular geometry, is evidenced both in the ground and in the excited electronic states. The electronic absorption spectra are characterized by low- to medium-intense charge-transfer bands that extend to the near-infrared.

Enhanced charge transfer in a monolayer of the organic charge transfer complex TTF–TNAP on Au(111)

Electronic doping is a key concept for tuning the properties of organic materials. In bulk structures, the charge transfer between donor and acceptor is mainly given by the respective ionization potential and electron affinity. In contrast, monolayers of charge transfer complexes in contact with a metal are affected by an intriguing interplay of hybridization and screening at the metallic interface, determining the resulting charge state. Using scanning tunneling microscopy and spectroscopy, we characterize the electronic properties of the organic acceptor molecule 11,11,12,12-tetracyanonaptho-2,6-quinodimethane (TNAP) adsorbed on a Au(111) surface. The ordered islands remain in a weakly physisorbed state with no charge transfer interaction with the substrate. When the electron donor tetrathiafulvalene (TTF) is added, ordered arrays of alternating TNAP and TTF rows are assembled. In these structures, we find the lowest unoccupied molecular orbital (LUMO) of the free TNAP molecule shifted well below the Fermi level of the substrate. The TNAP is thus charged with more than one electron.