TTF Donors Research Articles

Chiral Bis(tetrathiafulvalene)-1,2-cyclohexane-diamides.

Chiral bis(TTF) diamides have been obtained in good yields (54–74%) from 1,2-cyclohexane-diamine and the corresponding TTF acyl chlorides. The (R,R)-1 and (S,S)-1 enantiomers have been characterized by circular dichroism and the racemic form by single-crystal X-ray diffraction. The neutral racemic bis(TTF)-diamide shows the formation of a pincer-like framework in the solid state, thanks to the intramolecular S···S interactions. The chemical oxidation in a solution using FeCl3 provides stable oxidized species, while the electrocrystallization experiments provided radical cation salts. In particular, single-crystal resistivity measurements on the racemic donor with AsF6− as a counterion demonstrate semiconductor behavior in this material. The DFT and TD-DFT calculations support the structural and chiroptical features of these new chiral TTF donors.

Spectroscopic investigation of some electron withdrawing groups substituted TTF donor.

The structure optimization and spectroscopic properties for some derivatives of tetrathiafulvalene in both the neutral and ionized forms have been studied. The electron withdrawing groups like -CN, -CF3 and -CO2Me were considered to study the effect on structure, vibrational and electronic properties of tetrathiafulvalene. All the calculations were carried out at density functional theory incorporated with B3LYP exchange functional. The CAM-B3LYP exchange-correlation energy functional was also assessed for the determination of molecular structures. The normal coordinate analysis was performed to compute potential energy distributions of the normal modes which were used for the subsequent normal modes assignment. The temperature dependent Raman spectra have been presented showing the relative reduction in Raman intensity. The ionization of TTF-CN leads a very interesting effect. The IR spectrum of neutral TTF-CN contains a very strong CN stretching band at 2251cm-1 while it is completely diminished in IR spectrum of TTF-CN cation. NBO analyses were also performed to study the electronic structure, second order perturbation and HOMO-LUMO and their energies. Some important thermodynamical parameters have been presented in which entropy calculation reveals below 50% contribution of vibrational motion in all the three molecules.

Nanoscale "Noise-Source Switching" during the Optoelectronic Switching of Phase-Separated Polymer Nanocomposites.

A method is developed to directly map nanoscale "noise-source switching" phenomena during the optoelectronic switching of phase-separated polymer nanocomposites of tetrathiafulvalene (TTF) and phenyl-C61 -butyric acid methyl ester (PCBM) molecules dispersed in a polystyrene (PS) matrix. In the method, electrical current and noise maps of the nanocomposite film are recorded using a conducting nanoprobe, enabling the mapping of a conductivity and a noise-source density. The results provide evidence for a repeated modulation in noise sources, a "noise-source switching," in each stage of a switching cycle. Interestingly, when the nanocomposite is "set" by a high bias, insulating PS-rich phases shows a drastic decrease in a noise-source density which becomes lower than that of conducting TTF-PCBM-rich phases. This can be attributed to a trap filling by charge carriers generated from a TTF (donor)-PCBM (acceptor) complex. In addition, when the film is exposed to UV, an optical switching occurs due to chemical reactions which lead to irreversible changes on the noise-source density and conductivity. The method provides a new insight on noise-source activities during the optoelectronic switching of polymer nanocomposites and thus can be a powerful tool for basic noise research and applications in organic memory devices.

Tetrathiafulvalene-Polychlorotriphenylmethyl Dyads: Influence of Bridge and Open-Shell Characteristics on Linear and Nonlinear Optical Properties.

Three conjugated donor-π-acceptor radical systems (1 a-1 c) were prepared by bridging a tetrathiafulvalene (TTF) electron-donor unit to a polychlorotriphenylmethyl (PTM) electron-acceptor radical through vinylene units of different lengths. The dependence of the intramolecular charge transfer on the length of the conjugated bridge has been analyzed by different electrochemical and spectroscopic techniques. Linear optical properties and the second-order nonlinear optical (NLO) response of these derivatives have been computed by comparing systems 1 a-1 c with the non-radical analogues (2 a-2 c). Interestingly, an enhanced NLO response is predicted for dyads 1 a-1 c with PTM in the radical form and for compounds with longer vinylene bridges. Calculations confirm the active role the bridge plays for electronic communication between the donor TTF and the acceptor PTM units.

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.

TTFs nonsymmetrically fused with alkylthiophenic moieties.

Two new dithiolene ligand precursors, containing fused TTF and alkyl thiophenic moieties 3,3'-{[2-(5-(tert-butyl)thieno[2,3-d][1,3]dithiol-2-ylidene)-1,3-dithiole-4,5-diyl]bis[sulfanediyl]}dipropanenitrile (α-tbtdt, 1), and 3,3'-{[2-(5-methylthieno[2,3-d][1,3]dithiol-2-ylidene)-1,3-dithiole-4,5-diyl]bis[sulfanediyl]}dipropanenitrile (α-mtdt, 2), were synthesized and characterized. The electrochemical properties of these electronic donors were studied by cyclic voltammetry (CV) in dichloromethane. Both compounds show two quasi-reversible oxidation processes, versus Ag/AgCl, typical of TTF donors at E11/2 = 279 V and E21/2 = 680 V for 1 and E11/2 = 304 V and E21/2 = 716 V in the case of 2. The single-crystal X-ray structure of 1 and of a charge transfer salt of 2, (α-mtdt)[Au(mnt)2] (3), are reported.

Electronic Structure at the Interface between Rubrene and Perylenediimide Single Crystals: Impact of Interfacial Charge Transfer and its Modulation

DOI: 10.1002/admi.201400362 Density Approximation (LDA) and a semi-empirical correction to the bandgap. An interface geometry was assumed where TTF and TCNQ layers stack according to the TTF-TCNQ bulk crystal structure; [ 14 ] such an approach, however, neglects the fact that the individual single crystals of TTF and TCNQ display markedly different lattice parameters. As such, the interface between two single crystals can turn out to be very different from that of the corresponding co-crystal. Here, we go signifi cantly beyond these assumptions by carrying out molecular dynamics (MD) simulations of the organic D-A interface and DFT calculations at the semi-local and hybrid levels. X-ray diffraction (XRD) experiments on rubrene and PDIFCN 2 crystalline fi lms on bare or modifi ed SiO 2 /Si(100) substrates have shown preferential ( h 00) [ 15 ] and (00 l ) [ 16 ] exposures for the surfaces of rubrene and PDIF-CN 2 , respectively. Based on these experimental data, we assumed as a starting point that the orientations of the rubrene and PDIF-CN 2 crystalline thin fi lms at their interface are along the [100] and [001] directions of the respective crystal structures. (Note that a rotation operation has to be performed on the original coordinate system of the rubrene crystal to reorient its (100) surface to (001) in the new coordinate system describing the rubrene/ PDIF-CN 2 interface, see Figure 1 ). We then carried out MD simulations (see the “Computational Methodology” section and the Supporting Information for details) on a multilayer system consisting of three layers of rubrene original (100) in contact with three layers of PDIF-CN 2 (001) (with the orientations defi ned using the rubrene and PDIF-CN 2 crystal structures, respectively). We considered periodic boundary conditions with a supercell of 2.96 × 2.97 × 20 nm 3 , including a vacuum space of 12 nm along the z-direction (normal to the interface) to prevent spurious interactions between the multilayer slabs. Four equilibrated snapshots of the interface were taken with time intervals of 10 ps. The MD results point out that the interactions between the two crystalline thin fi lms are mainly limited to the very top layer of rubrene and the bottom layer of PDIF-CN 2 . This is further confi rmed by electronic-structure calculations at the DFT level where we consider a four-layer interface system consisting of two layers of each molecular component (see Section C and Figure S4 in the Supporting Information). Therefore, out of the equilibrated snapshots, four independent rubrene/PDIFCN 2 bilayer confi gurations were extracted and served as input for the DFT calculations (size: 0.74 × 1.485 nm 2 within the x-y plane based on the periodicity of the rubrene crystal). Each surface unit cell for the DFT calculations contains two rubrene and two PDIF-CN 2 molecules (with 2-D periodicity of the rubrene (100) surface along the xand y-directions) and a vacuum space Charge transfer at organic donor-acceptor (D-A) interfaces is one of the fundamental processes in organic (opto)electronic devices, such as organic solar cells –where effi cient exciton dissociation and charge separation only occurs at or near the D-A interface– or organic light-emitting diodes –where a critical step is electron-hole recombination. [ 1–4 ] A few years ago, Morpurgo and co-workers uncovered a new phenomenon at the organic D-A interface formed between tetrathiafulvalene (TTF) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) single crystals; a metallic conduction at the interface was demonstrated due to signifi cant electron transfer between adjacent layers from the donor TTF to the acceptor TCNQ. [ 5 ] Following this work, a number of studies have highlighted the electrical transport properties and photoconductive response of other organic D-A systems with well-defi ned interfaces. [ 6–11 ] Recently, Morpurgo and co-workers have reported peculiar electrical-transport characteristics at the interface formed between rubrene and N , N′ -1 H ,1 H -perfl uorobutyldicyanoperylenecarboxydiimide (PDIF-CN 2 ) single crystals. In that instance, they found that the electron carrier density has a linear dependence with temperature, pointing to a very-small-to-vanishing bandgap, with the carrier mobility exhibiting band-like behavior around room temperature and remaining as high as 1 cm 2 V −1 s −1 at 30 K. [ 6 ]

A New Type of Charge-Transfer Salts Based on Tetrathiafulvalene–Tetracarboxylate Coordination Polymers and Methyl Viologen

Although charge-transfer compounds based on tetrathiafulvalene (TTF) derivatives have been intensively studied, {[cation](n+)·[TTFs](n-)} ion pair charge-transfer (IPCT) salts have not been reported. The aim of this research is to introduce functional organic cations, such as photoactive methyl viologen (MV(2+)), into the negatively charged TTF-metal coordination framework to obtain this new type of IPCT complex. X-ray structural analysis of the four compounds (MV)2[Li4(L)2(H2O)6] (1), {(MV)(L)[Na2(H2O)8]·4H2O}n (2), {(MV)[Mn(L)(H2O)2]·2H2O}n (3), and {(MV)[Mn(L)(H2O)2]}n (4), reveals that the electron donor (D) TTF moiety and the electron acceptor (A) MV(2+) form a regular mixed-stack arrangement in alternating DADA fashion. The TTF moiety and the MV(2+) cation are essentially parallel stacked to form the column structures. The strong electrostatic interaction is a main force to shorten the distance between the cation and anion planes. Optical diffuse-reflection spectra indicate that charge transfer occurs in these complexes. The ESR and magnetic measurements confirm that there is strong charge-transfer-induced partial electron transfer. Compounds 2, 3, and 4 show an effective and repeatable photocurrent response. The current intensities of 3 and 4 are higher than that of 2, which reflects that the coordination center of the Mn(II) ion has a great effect on the increasing photocurrent response.

Electronic tuning effects via π-linkers in tetrathiafulvalene-based dyes

Four new tetrathiafulvalene (TTF)-based dyes featured with a donor–bridge–acceptor (D–π–A) structure were synthesized and characterized. All of them undergo two reversible oxidations to form stable radical cation and dication species. The electronic interactions between the TTF donor and the cyanoacrylic acid acceptor through the different π-linkers have been demonstrated by the presence of a photo-induced intramolecular charge-transfer (ICT) absorption band in the visible region. A red shift of the ICT state can be finely tuned by the degree of aromaticity and extended conjugation of π-bridges. To some extent, the oxidation potentials of these dyes are affected by the nature of π-bridges. They have been applied in organic dye-sensitized solar cells, showing relatively low power conversion efficiencies of up to 0.87% due to substantial charge recombination losses.

Electroactive tetrathiafulvalene based pyridine-mono and -bis(1,2,3-triazoles) click ligands: synthesis, crystal structures and coordination chemistry

Electroactive ligands picoline-1,2,3-triazole-5-DM-TTF and lutidine-bis(1,2,3-triazole-5-DM-TTF) are synthesized by click chemistry following the ruthenium catalyzed azide–alkyne cycloaddition strategy. In the solid state structure of the bis(triazole) derivative, a tweezer conformation is observed, with the two TTF units arranged in a parallel manner. Cyclic voltammetry measurements show a splitting of the first oxidation wave, demonstrating sequential oxidation of the TTF donors in the intramolecular in through space mixed valence radical cation and then dication, suggesting that the tweezer conformation is maintained also in solution. A cobalt(II) complex based on the chelating picoline-triazole ligand is described. The lutidine-bis-triazole ligand shows no chelating behavior in the two structurally reported cadmium(II) complexes. In one of the complexes, the Cd(II) center is coordinated by four triazole rings from four different ligands, while the other four triazole units establish hydrogen bonds with one axially coordinated water molecule. The second complex is a one-dimensional coordination polymer, containing the CdCl2 fragment, in which the repeating motif is a pentanuclear “Cd5Cl10” unit decorated with two TTF ligands coordinated in a ditopical mode through the triazole units. The TTF donors establish intra- and intermolecular S⋯S contacts.

A Tris-fused Tetrathiafulvalene Extended with Cyclohexene-1,4-diylidene: A New Positive Electrode Material for Organic Rechargeable Batteries

Abstract Derivatives of tris-fused TTF donors 3 extended with cyclohexene-1,4-diylidene were synthesized. Cyclic voltammetry revealed that the tetrakis(hexylthio)-3 (3c) exhibited three stages of a two-electron redox process to afford the hexacation. The rechargeable battery incorporating tetrakis(methylsulfanyl)-3 (3b) as the positive electrode material exhibited a high cycle performance in spite of utilizing the highest oxidation state of +6.

Conductive PVDF-HFP Nanofibers with Embedded TTF-TCNQ Charge Transfer Complex

Tetrathiafulvalene-tetracyanoquinodimethane charge-transfer complex (TTF-TCNQ CTC) represents a promising organic conductive system. However, application of this donor-acceptor pair is highly limited, because of its ultrafast crystallization kinetics and very low solubility. In this work, conductive organic nanofibers were generated via a coelectrospinning process of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) with embedded TTF and TCNQ in the shell and core solutions, respectively. Upon supply of the polymer solutions, a core-shell droplet was formed at the exit of the spinneret. The electron donor TTF and the electron acceptor TCNQ migrated toward each other, within the compound droplet, to produce conductive CTC crystals. In the presence of a sufficiently strong electric field, jetting set in at the droplet tip, which yielded solidified PVDF-HFP nanofibers embedded with aligned CTC. Fiber diameters ranged between 100 and 500 nm. X-ray analysis showed strong equatorial reflections (110,200) of oriented copolymer PVDF-HFP crystals (β-phase) with copolymer chains oriented along the fiber axis, and of CTC (001), indicating that the CTC molecular planes were aligned parallel to the nanofiber axis. In addition, reflections of unreacted TCNQ (120,220) and TTF (110) crystals were observed. The electrospun nanofibers were collected to form a fiber mat, which was evaluated as a working electrode in a three-electrode cell system, exhibiting differential conductance of 5.23 μmho.

α‐Dithiophene‐tetrathiafulvalene – a Detailed Study of an Electronic Donor and Its Derivatives

AbstractThe electronic donor α‐DT‐TTF (α‐dithiophene‐tetrathiafulvalene), which among the thiophenic TTF derivatives has remained essentially unexplored, and some of its charge transfer salts are described in detail in this paper. This donor was efficiently prepared by the homocoupling of 5,6‐thieno[2,3‐d]‐1,3‐dithiol‐2‐one, and its redox properties are intermediate between those of DT‐TTF (dithiophene‐tetrathiafulvalene) and BET‐TTF [bis(ethylenethio)tetrathiafulvalene]. The crystal structure of α‐DT‐TTF shows a molecular packing composed of trios of donor chains with alternating orientation. This pattern is clearly distinct from those previously found in all other thiophenic TTF donors. Used as an active material in a field‐effect transistor, α‐DT‐TTF presents a mobility μFE = 5 × 10–5 cm2/V s. The possibility to convert this new donor to conducting charge‐transfer salts with suitable anions was demonstrated by preparing its PF6– salts. Two salts with different crystal structures and stoichiometries were identified by X‐ray diffraction studies: (α‐DT‐TTF)(PF6)0.6 and (α‐DT‐TTF)2(PF6). The electrical conductivities of these salts, measured in the single crystal, range from 9 to 50 S/cm at room temperature. In all cases, the salts show a semiconducting behaviour and properties that are comparable to those of the analogous nonaromatic BET‐TTF salts.

A sum rule for inelastic electron tunneling spectroscopy: an ab initio study of a donor (TTF) and acceptors (TCNE, TCNQ and DCNQI) parallelly oriented on Cu(100)

We performed first-principles simulations of Inelastic Electron Tunneling Spectroscopy (IETS) for horizontally lying individual molecules that form popular donor-acceptor pairs (the TTF donor and its possible partner acceptors TCNE, TCNQ and DCNQI) on Cu(100). We find that the highest frequency C-H stretching modes are highly active for the (electron-rich) donor molecule but inactive for the (electron-poor) acceptors. We explain this contrasting response by the spatial extension of sp(3) rehybridization upon adsorption: the donor molecule entirely deforms into sp(3) while the acceptors rehybridize only at their outer ends leaving the central spacer unaffected. The sp(3)-induced buckling permits in-plane vibration modes to overlap with the π-type tunneling states and hence to be detected in IETS. In addition, the IET-spectra of a family of cyano-group acceptors, TCNE, TCNQ and DCNQI, show a recurring pattern of signals from vibrations involving their common CN outer ends plus a set of compound-dependent signals arising from the spacing moiety. The IET-response of individual chemical groups thus adds up for these flat-lying acceptor molecules, evidencing a sum rule that may facilitate their identification.

4，5-ジアザフルオレン骨格を有する金属配位型ＴＴＦドナー分子の合成

4，5-ジアザフルオレン骨格を有する金属配位型ＴＴＦドナー分子の合成

Coupling Tetracyanoquinodimethane to Tetrathiafulvalene: A Fused TCNQ–TTF–TCNQ Triad

Happy marriage: For the first time, a fused TCNQ–TTF–TCNQ triad has been synthesized and structurally characterized. Strong bending is observed in both the TTF bridge and the benzo-TCNQ moieties, which prevents good packing for intermolecular charge transfer. The Vis/NIR and VT-EPR studies of the mixed-valence derivative of the triad indicate that the electrons are moving from one acceptor moiety to the other through the donor TTF bridge.

A tetrathiafulvalene–perylene diimide conjugate prepared via click chemistry

A new tetrathiafulvalene (TTF)–perylene diimide (PDI) conjugate is prepared from an azide-functionalized TTF and an acetylenic PDI employing a Cu(I)-catalyzed Huisgen-Meldal-Sharpless reaction (‘click chemistry’). Thus, the TTF donor and PDI acceptor units are linked together by a 1,2,3-triazole unit. The molecules are found to assemble on a mica surface, forming fibrilar structures.

STM study on the charge order phase of θ–(BEDT–TTF)2RbZn(SCN)4

Abstract The organic conductor θ – ( BEDT – TTF ) 2 RbZn ( SCN ) 4 , which exhibits charge ordering below T CO = 190 K , was studied by STM to observe the charge ordering pattern in the real space. The conducting a – c plane was investigated. The donor arrangement in the a – c surface was clearly observed in topographic STM images at room temperature. The STM image shows the rectangular pattern with periods of 1 nm and 0.5 nm along the a - and c -direction, respectively. This means that BEDT–TTF donors located at the center of the rectangle were not observed except a certain scan. The observed STM image is naively expected from the crystal structure of θ – ( BEDT – TTF ) 2 RbZn ( SCN ) 4 . We found that all donors can be imaged by the scan along the a -axis. The STM image at 170 K shows the nearly two-fold periodicity along the c -direction. It corresponds to the horizontal stripe charge order pattern.

Tetrapyridine and Tetrapyrazine TTF Derivatives: Synthesis, Characterization and Preparation of a Bimetallic CoII Complex

AbstractThe tetra‐substituted TTF‐type donors 4,4′,5,5′‐tetrakis(2‐pyridylethylsulfanyl)tetrathiafulvalene (1) and 4,4′,5,5′‐tetrakis(2‐pyrazylethylsulfanyl)tetrathiafulvalene (2) were prepared and characterized. These donors show a redox behaviour that is comparable with similar unsubstituted TTF donors, with a small increase of the redox potentials due to the electron‐withdrawing effect of the pyridine and pyrazine groups. Single crystal X‐ray diffraction analyses show structures with a strong segregation of TTF and azo moieties. The pyridine‐substituted donor 1 was used as a bridging ligand to prepare a dinuclear CoII‐coordination complex [1Co2(hfac)4] (hfac = hexafluoroacetylacetonate) with redox properties identical to that of 1. This dinuclear complex presents an effective magnetic moment of ca. 8 μB, corresponding to nearly independent S = 3/2 spins with weak antiferromagnetic interactions below 65 K. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Molecular Complexes Based on Tetrathiafulvalene and Dialkylviologens

Three kinds of molecular complexes based on tetrathiafulvalene (TTF) and dialkylviologens were prepared and their crystal structures elucidated. While TTF-dimethylviologen complex forms a mixed stack arrangement of donors and acceptors in its crystal structure, TTF donors aggregate with long alkyl groups by CH/pi and/or van der Waals interactions in a couple of TTF-heptylviologen complexes.