TTF Molecules Research Articles

A First-Principles Study on Electron Donor and Acceptor Molecules Adsorbed on Phosphorene

Density functional theory calculations have been carried out to investigate single-layer phosphorene functionalized with two kinds of organic molecules, i.e., an electrophilic molecule tetracyano-p-quinodimethane (TCNQ) as electron acceptor and a nucleophilic molecule tetrathiafulvalene (TTF) as electron donor. The TCNQ molecule introduces shallow acceptor states in the gap of phosphorene close to the valence band edge, which makes the doped system become a p-type semiconductor. However, when the TTF molecule is adsorbed on the phosphorene, the occupied molecular states introduced into the gap are of deep donor states so that effective n-doping for transport cannot be realized. This disadvantageous situation can be amended by applying an external out-of-plane electric field with direction from phosphorene to TTF, or an in-plane tensile strain, or their combination, under which the conduction band edge of the phosphorene moves closer to the TTF-derived donor states, and then the TTF-adsorbed phosphorene system becomes an n-type semiconductor. It is also noted that the out-of-plane electric field and in-plane strain can modulate the band gap of the TTF-adsorbed phosphorene markedly. The effective bipolar doping of single-layer phosphorene via molecular adsorption, especially n-doping against its native p-doping propensity, and the good response of band gap in the infrared waveband of the TTF-adsorbed phosphorene to the out-of-plane electric field and in-plane strain would broaden the way to the application of this new type of two-dimensional material in nanoelectronic and optoelectronic devices.

Abstract 2675: Optimization of antivascular tumor therapy with retargeted tissue factor proteins to improve the activity/toxicity profiles and therapeutic outcome

Abstract The purpose of this study is to improve the safety and activity profile of therapeutic tumor vascular infarction using retargeted tissue factor-(tTF-) by in vitro- and in-vivo analysis of 1. newly generated tTF fusion proteins, 2. site-specific and randomly PEGylated tTF-NGR protein, 3. combination therapy with radiation, cytotoxics, low-energy ultrasound, and by 4. using different routes of application. Experimental procedures Molecular cloning strategies and site-directed mutagenesis were used to generate new tTF constructs. Coupling of polyethylene glycol (PEG) units to the recombinant tTF proteins was performed by site-directed and random PEGylation and coupling of non-peptidic ligands was performed by maleimide-activated reagents. The biological ability of the tTF-fusion proteins to induce coagulation was assessed by a FX assay. The differential binding of fusion proteins to HUVECs and HuAoSMCs was analyzed by FACS. For the in-vivo evaluation of tumor growth, immunodeficient CD-1 nude mice were transplanted with various human tumor xenotransplants. The anti-vascular mechanism was verified by the molecular imaging methods SPECT, MRI, FRI, and CEUS. Results To improve the specificity of the therapy, novel fusion proteins were constructed which are supposed to selectively target the receptor protein NG2 on tumor vessel pericytes. The newly synthesized tTF-TAA/-LTL fusion proteins retained their thrombogenic activity and specific binding to the pericyte marker NG2 in vitro; first therapeutic trials with tumor-bearing mice revealed a comparatively small therapeutic range. The conjugation of tTF-NGR with low-molecular PEG-chains improved the therapeutic range of the tTF-fusion protein substantially, together with increased in-vivo tolerance. Moreover, site-directed PEGylated of cysteinated tTF molecules were constructed and revealed promising analytical and in-vitro thrombogenic effects. Cysteinated tTF (tTF-C) acts as fast and convenient “building block” for non-peptidic ligands of receptor proteins overexpressed in the tumor vasculature (such as CD13, αV-integrins etc.). Combination therapies of tTF-NGR with doxorubicin, irradiation, or low-energy-ultrasound, respectively, showed synergistic effects. Conclusion Promising results have been achieved to optimize the anticancer profile of tumor-vessel infarction by retargeted tTF: The therapeutic range of the tTF-NGR fusion protein has been improved by PEGylation and by combination with either radiation, chemotherapy with doxorubicin, or low-energy ultrasound, respectively. Ongoing experiments further optimize this anti-vascular therapy by using new (PEG) polymers. Citation Format: Christian Schwöppe, Caroline Zerbst, Christoph Schliemann, Rolf M. Mesters, Wolfgang E. Berdel. Optimization of antivascular tumor therapy with retargeted tissue factor proteins to improve the activity/toxicity profiles and therapeutic outcome. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2675. doi:10.1158/1538-7445.AM2014-2675

Inclusion complexes of fullerenes with flexible tetrathiafulvalene derivatives bearing four aryls through sulfur bridges

TTF derivatives decorated with four aryls through the sulfur bridges are employed to form the donor–acceptor type inclusion complexes with fullerenes. The key factor for the formation of inclusion complexes is the introduction of structural flexibility in TTF molecules along with the molecular size matching with fullerenes. A crystallographic study indicates that the structures of the resulting complexes are stabilized by a multidimensional intermolecular interaction network consisting of TTF cores, peripheral aryls, and fullerenes, which in turn gives rise to the electronic communication between the donor and the acceptor as proved by the solid state absorption spectra. Moreover, the fullerene molecules form the two-dimensional sheet structure in the complexes.

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.

First principles study on molecule doping in MoS2 monolayer

The chemical doping of organic molecules adsorbed on MoS2 monolayers are systematically studied by using plane-wave pseudo-potential method based on the density functional theory. Our results indicate that the interaction between organic molecules and the MoS2 monolayer substrate is of van der Waals' type of force. Structure of monolayer MoS2 which adsorbs different organic molecules, exhibits indirect bandgap characteristics, and the energy band structure of monolayer MoS2 which adsorbs TTF molecules exhibits n-type conducting characteristics. However, the structures of monolayer MoS2 which adsorbs TCNQ or TCNE molecules would exhibit p-type conductivity characteristics. Thus, the results indicate that the doping type of molecules in monolayer MoS2 can be regulated by adsorbing different molecules. Results of this study may provide a theoretical basis for single-layer MoS2 transistor and guidance for it in the application.

Barrier height formation in organic blends/metal interfaces: Case of tetrathiafulvalene-tetracyanoquinodimethane/Au(111)

The interface between the tetrathiafulvalene/tetracyanoquinodimethane (TTF-TCNQ) organic blend and the Au(111) metal surface is analyzed by Density Functional Theory calculations, including the effect of the charging energies on the molecule transport gaps. Given the strong donor and acceptor characters of the TTF and TCNQ molecules, respectively, there is a strong intermolecular interaction, with a relatively high charge transfer between the two organic materials, and between the organic layer and the metal surface. We find that the TCNQ LUMO peak is very close to the Fermi level; due to the interaction with the metal surface, the organic molecular levels are broadened, creating an important induced density of interface states (IDIS). We show that the interface energy level alignment is controlled by the charge transfer between TTF, TCNQ, and Au, and by the molecular dipoles created in the molecules because of their deformations when adsorbed on Au(111). A generalization of the Unified-IDIS model, to explain how the interface energy levels alignment is achieved for the case of this blended donor/acceptor organic layer, is presented by introducing matrix equations associated with the Charge Neutrality Levels of both organic materials and with their intermixed screening properties.

Synthesis and studies of a novel [(Tetrathiafulvalene)-(2-Amino-6-nitrobenzothiazole)2] co-crystal

A novel 2-Amino-6-nitrobenzothiazole (2A6NBT) complex of tetrathiafulvalene (TTF) was synthesized and crystal structure of (TTF)-(2A6NBT)2 is reported. The asymmetric unit is found to have half molecule of TTF and one molecule of 2-Amino-6-nitrobenzothiazole. Several short interactions of type π–π, nonconventional Van der Waals and hydrogen bonding were observed in this complex. Localization of the inversion center lead to the presence of 2A6NBT moieties in the trans position. Van der Waals type short interactions existed predominantly between one TTF and six 2A6NBT molecules. The C–C bond length of 1.314Å in (TTF)-(2A6NBT)2 is the shortest C–C bond distance reported among the TTF molecules studied so far. TTF's and 2A6NBT molecules are nearly orthogonal to each other. TTF form segregated stacks along the c axis and exhibit a novel “stair case” structure. The extensive short interactions lead to supramolecular architectures. Two probe room temperature conductivity value of powder was (∼1.4×10−7S/cm) found to be within the semiconducting range measurements. Density functional calculations using the hybrid functional B3LYP with 6–31G (d) basis set indicated thermodynamically favored product. Scanning electron microscopy images revealed rod like microstructures.

Bulk-Sensitive Angle-Resolved Photoemission Spectroscopy on TTF-TCNQ

TTF-TCNQ is a quasi-1D molecular conductor exhibiting metal-insulator transition at 54K accompanied by chargedensity-wave (CDW) formation. Its electronic properties in relation to the Peierls instability and CDW transitions are well investigated through the several decades. Past ARPES studies indicate the band dispersion consisting of TCNQ molecules (namely the TCNQ-band) shows the signature of spin–charge separation, together with the suppression of the quasiparticle excitation at the Fermi level. These observations have been discussed in terms of the 1D character of TTF-TCNQ, nevertheless, there are several mysteries remained. One is the band dispersions obtained by ARPES commonly indicating the band-width (or the band group velocity) larger by a factor of 2 with respect to band theory. To account for this discrepancy, the possibility of relaxed tilting of the topmost molecules and/or strong correlation effect have been raised until now. The second is the anomalous suppression of the spectral weight near the Fermi level (EF), which gives negligible amount of spectral intensity at EF even in the highly-conductive state above >60K. The electronic structure of the metallic quasi-1D state has been thus remained to be elucidated. To investigate the precise electronic structure of TTFTCNQ, here we utilized the laser-excited ARPES with h 1⁄4 6:994 eV. Owing to the relatively low photon-energy as compared with past ARPES studies (h 1⁄4 20{40 eV), the bulk-sensitive measurement becomes available. The effect of photoirradiation-induced damage peculiar to molecular compounds is also considered to be weaker compared to the measurements using higher-energy photons. The high cross section of s and p electrons for this photon-energy provides some advantage in studying the light-element based organic conductors. ARPES measurements were performed using a system constructed with VG-Scienta R4000 electron analyzer and an ultraviolet (h 1⁄4 6:994 eV) laser. He II (h 1⁄4 40:8 eV) light source was also used to check the correspondence with past reports. Single crystals of TTF-TCNQ grown by the diffusion method were cleaved in-situ to obtain fresh surfaces. The pressure was below 5 10 11 Torr throughout all the measurements. The energy resolution was E 1⁄4 4:0meV. The Fermi level EF of the sample was referred to that of a Au film evaporated on the sample substrate, with an accuracy of 0:1meV. Figure 1(a) shows the mapping of the ARPES intensity (h 1⁄4 6:994 eV) at the Fermi level, obtained by integrating the ARPES intensity in the energy window of 50meV. The shape of the Fermi surface thus observed makes a straight line at kF 1⁄4 0:24 0:01 A 1 1⁄4 ð0:29 0:01Þb , indicative of 1D electronic structure. The image of band dispersions along –Z direction obtained by h 1⁄4 6:994 and 40.8 eV are shown in Fig. 1(b,c). The peak positions of the ARPES intensity estimated from momentum distribution curve (MDC) and energy distribution curve (EDC) are plotted by circle and cross markers, respectively. The red and blue curves, on the other hand, represent the band dispersions consisting of TTF and TCNQ molecules, obtained by the first-principles calculation. By comparing with the band calculation, we can notice that the h 1⁄4 6:994 eV data is dominated by the signal from TTF bands, whereas the h 1⁄4 40:8 eV data shows both TTF and TCNQ bands that are well in accord with past reports. This h -dependence, which should be due to the photoionization cross section and/or matrix element effect, also explains the slight difference of the present ‘‘Fermi-surface’’ shape from that previously reported. The Fermi momentum obtained by ARPES, kF 1⁄4 0:24 0:01 A , is somewhat smaller compared with the band calculation, reflecting the overestimation of the charge transfer between TTF and TCNQ inevitably arising in the calculated data. Here, let us focus on the gradient of the TTF band dispersion. In the h 1⁄4 40:8 eV ARPES spectrum, the gradient of the TTF band dispersion is about 2 times larger as compared to the calculation. It shows that the observed High

Theoretical Study of the Interaction of Electron Donor and Acceptor Molecules with Graphene

With the aim of understanding recent experimental data concerning noncovalent n/p-doping effects in graphene samples, we have investigated the interactions between two prototypical donor and acceptor molecules and graphene mono- and bilayer systems, by means of density functional theory calculations. We report and rationalize the structural, thermodynamical aspects, as well as charge transfers and the induced electronic structure modifications of the graphenic substrates in interaction with tetrathiafulvalene (TTF), an organic donor molecule, and tetracyanoethylene (TCNE), a typical acceptor. If the results show that p-doping of a graphene monolayer due to TCNE molecules can occur even at low concentration, n-doping of graphene requires either larger concentrations or cooperative adsorption of TTF molecules. In both cases, noncovalent doping only implies shifts of the Fermi level, and keeps the linear dispersion of the π and π* state around the Dirac point. Moreover, the intercalation of donor/acceptor molecules decouples the layers and doped them.

Biophysical and RNA Interference Inhibitory Properties of Oligonucleotides Carrying Tetrathiafulvalene Groups at Terminal Positions

Oligonucleotide conjugates carrying a single functionalized tetrathiafulvalene (TTF) unit linked through a threoninol molecule to the 3′ or 5′ ends were synthesized together with their complementary oligonucleotides carrying a TTF, pyrene, or pentafluorophenyl group. TTF‐oligonucleotide conjugates formed duplexes with higher thermal stability than the corresponding unmodified oligonucleotides and pyrene‐ and pentafluorophenyl‐modified oligonucleotides. TTF‐modified oligonucleotides are able to bind to citrate‐stabilized gold nanoparticles (AuNPs) and produce stable gold AuNPs functionalized with oligonucleotides. Finally, TTF‐oligoribonucleotides have been synthesized to produce siRNA duplexes carrying TTF units. The presence of the TTF molecule is compatible with the RNA interference mechanism for gene inhibition.

Density functional theory for the description of charge-transfer processes at TTF/TCNQ interfaces

In the field of organic electronics, a central issue is to assess how the frontier electronic levels of two adjacent organic layers align with respect to one another at the interface. This alignment can be driven by the presence of a partial charge transfer and the formation of an interface dipole; it plays a key role for instance in determining the rates of exciton dissociation or exciton formation in organic solar cells or light-emitting diodes, respectively. Reliably modeling the processes taking place at these interfaces remains a challenge for the computational chemistry community. Here, we review our recent theoretical work on the influence of the choice of density functional theory (DFT) methodology on the description of the charge-transfer character in the ground state of TTF/TCNQ model complexes and interfaces. Starting with the electronic properties of the isolated TTF and TCNQ molecules and then considering the charge transfer and resulting interface dipole in TTF/TCNQ donor–acceptor stacks and bilayers, we examine the impact of the choice of DFT functional in describing the interfacial electronic structure. Finally, we employ computations based on periodic boundary conditions to highlight the impact of depolarization effects on the interfacial dipole moment.

Tetrathiofulvalene and tetracyanoquinodimethane crystals: Conducting surface versus interface

When a tetrathiofulvalene (TTF) crystal is placed onto a 7,7,8,8‐tetracyanoquinodimethane (TCNQ) crystal at room temperature, a highly conducting layer is formed. In this study, we explore to what degree this is due to physical contact or transfer by sublimation of one species onto the other crystal. We have performed a variety of time‐dependent surface conductivity measurements, including TTF lamination on TCNQ at room temperature and low temperatures, as well as deposition of TTF molecules from the gas phase. Crystal-to-crystal contact insignificantly modifies material conductivity while TTF sublimation onto TCNQ is shown to dominate electronic modification.

Bulk heterojunction photovoltaic cells based on room temperature liquid crystalline tetrathiafulvalene derivatives

We synthesised a tetrathiafulvalene (TTF) derivative having an asymmetric structure of a TTF mesogenic core and long alkyl chains which shows a highly ordered columnar liquid crystalline phase at room temperature. A bulk heterojunction photovoltaic cell was fabricated by using the TTF liquid crystal compound (a-6TTF12) as an electron donor and [6,6]-phenyl C61-butyric acid methyl ester (PC60BM) as an electron acceptor. The photoconversion efficiency (PCE) of the cell was very low (0.063%) as prepared, which increased to 0.120% after thermal annealing at 80°C for 20 min. The annealing effect was investigated by means of UV spectroscopy, X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) and energy-dispersive X-ray spectroscopy (EDS). The morphological observations of the annealed a-6TTF12: PC60BM composite film indicate that the higher PCE was attributed to the enhanced ordering of TTF molecules by the thermal annealing process to form a highly ordered columnar structure, which results in better charge-carrier mobility.

Preparation of graphene/tetrathiafulvalene nanocomposite switchable surfaces

A one step process for simultaneous reduction and functionalization of graphene oxide using tetrathiafulvalene (TTF) is described. Chemical oxidation of TTF to TTF(2+) using an aqueous solution of Fe(ClO(4))(3) expels the charged molecule from the graphene nanosheets, while subsequent immersion in neutral TTF solution allows the capture of the TTF molecules.

Structural and Electronic Properties of the TTF/ZnO(10–10) Interface: Insights From Modeling

The structural and electronic properties of a tetrathiafulvalene (TTF) monolayer adsorbed onto the ZnO(10–10) surface are investigated by using two different quantum-chemical approaches, namely, density functional theory and the self-consistent charge density functional-parametrized tight binding method. The two approaches yield strong hybridization of the highest occupied molecular orbital (HOMO) level of the TTF molecules with band states of ZnO in the most stable interfacial geometric configuration, which results in the pinning of the corresponding orbital in the hybrid system and a significant charge transfer across the interface. As a consequence, the work function of ZnO is significantly reduced. We discuss these results in the context of the design of new hybrid opto-electronic devices, where the deposition of organic layers onto inorganic surfaces allows modulating the barrier height for charge injection.

SPECTROSCOPIC STUDIES OF HYBRID THIN FILMS CONSISTING OF A CLAY AND TETRATHIAFULVALENE

We fabricated novel hybrid films consisting of a clay and cationic tetrathiafulvalene (TTF). The average distance between the TTF molecules adsorbed onto the clay sheet was controlled by changing the fabricating condition. The obtained films showed the absorption bands at around 450, 750 and 2000 nm, which were assigned to an intramolecular transition of TTF + , and intermolecular transitions between TTF + s and between TTF + and TTF°, respectively. The relative absorbances of the bands were found to vary depending on the average distance between the TTF molecules adsorbed onto the clay sheet. This fact indicates that the electronic properties of the TTF molecules in the present films can be controlled by changing the fabricating condition.

Four-Electron Oxygen Reduction by Tetrathiafulvalene

The four-electron reduction of oxygen by tetrathiafulvalene (TTF) in acidified 1,2-dichloroethane and at the acidified water/1,2-dichloroethane interface has been observed. Spectroscopy and ion transfer voltammetry results suggest that the reaction proceeds by the fast protonation of TTF followed by the 4-electron reduction of oxygen to form water. Electronic structure computations give evidence of the formation of a helical tetramer assembly ([TTF(4)H(2)](2+)) of two protonated TTF and two neutral TTF molecules. The protonated tetramer is potentially able to deliver the four electrons needed for the oxygen reduction. The production of water was corroborated by (1)H NMR analysis.

New method of accurate estimation of the electron–phonon coupling constants in fractionally charged incommensurate electronic states in molecular systems

The electron-phonon interactions in the fractionally positively charged incommensurate tetrathiafulvalene (TTF) molecular systems are investigated. In particular, since there are fractionally positive charges per TTF molecule, it is very difficult to estimate the vibronic and electron-phonon coupling constants, and thus there have been no reports of the exact calculations in the electron-phonon coupling constants in such fractionally positively charged incommensurate systems. Therefore, in this paper, we suggest new method of accurate estimation of the electron-phonon coupling constants in the fractionally positively charged systems. Total electron-phonon coupling constants for the monocation (l(+100)) of TTF is compared with that for the monoanion (l(-100)) of tetracyanoquinodimethanide (TCNQ). Furthermore, logarithmically averaged phonon frequency for the monocation (ν(ln , +1.00)) of TTF is compared with that for the monoanion (ν(ln , -1.00)) of TCNQ. The C-C and C-S stretching mode of 1599 cm(-1) and the C-S-C and C-C-S bending mode of 472 cm(-1) strongly couple to the b(3)u highest occupied molecular orbital (HOMO) in TTF molecule. The l(+100) value for TTF molecule is estimated to be 0.274 eV, and the ν(ln , +1.00) value for TTF molecule is estimated to be 926 cm(-1). The density of states at the Fermi level (N(NM, crystal)(ε(F))(+0.59, +0.59)) values for TTF(0.59+), which are essential physical values in order to investigate the mechanisms of the non-Ohmic current-voltage characteristics excellently suggested by Cohen and Heeger et al., are also estimated. By comparing the N(NM, crystal)(ε(F))(+0.59, +0.59) values estimated by us with those estimated from the experimental results of the Pauli susceptibility and the current-voltage characteristics in TTF(0.59+) suggested by Cohen and Heeger et al., and from the band calculations, we show that the l(+0.59), ν(ln , +1.00), RE(+0.59), and N(NM, crystal)(ε(F))(+0.59, +0.59) values estimated by our new calculation method are very accurate and reliable.

Ab Initio Powder Diffraction Structure Analysis of a Host–Guest Network: Short Contacts between Tetrathiafulvalene Molecules in a Pore

Many crystal structures of porous coordination networks have been solved by single-crystal X-ray crystallography, providing detailed molecular structural information on framework, guest arrangement, and even reactive intermediates generated in situ. Such detailed structural analysis facilitated the explosive development of porous coordination networks in the last 15 years. On the other hand, although there are many examples of ab initio powder X-ray diffraction (PXRD) analysis of inorganic materials, organic solids, nonporous coordination networks, and discrete small molecules, there are only few reports of ab initio PXRD analysis of porous coordination networks describing guest behavior (guest exchange, gas adsorption, etc.). This is because ab initio PXRD analysis is considerably more challenging than singlecrystal structure determination. Porous coordination networks usually have large unit cells and often low symmetry that contribute to severe peak overlap which hampers accurate structure determination. By using high-resolution synchrotron PXRD and the simulating annealing method, we have now succeeded in solving the crystal structure of a biporous coordination network having an unprecedented arrangement of tetrathiafulvalene (TTF) molecules and a unit cell larger than 15000 . The PXRD analysis revealed very short intermolecular S···S contacts between TTF molecules (3.370 ) that have a nonplanar shape indicating a neutral form. Those findings agree with solid-state spectroscopic features. A key issue in inducing intriguing physical properties in TTF is how to arrange the molecules. We tried to achieve a unique arrangement of TTF molecules by using the pores of a porous coordination network. We used the previously reported network [(ZnI2)3(1)2(2)]n·xC6H5NO2·yCH3OH (3, where 1 is 2,4,6-tris(4-pyridyl)-1,3,5-triazine (TPT) and 2 is triphenylene; x 4 and y 2) and prepared new isostructural ZnBr2 network 4 (Scheme 1) by instant synthesis. [3b]

Photoinduced Triplet States of Photoconductive TTF Derivatives Including a Fluorescent Group

Abstract The spin dynamics of photoconductive tetrathiafulvalene (TTF) derivatives containing 2,5-diphenyl-1,3,4-oxadiazole (PPD) was examined using time-resolved electron spin resonance (TR-ESR) spectroscopy. TR-ESR signals of a frozen solution sample under visible excitation were attributed to the excited triplet state T1, which was populated via intersystem crossing from the excited singlet state S1 as confirmed by TR-ESR spectral simulations. From DFT calculations, the spin-density distribution of the T1 state was found to be concentrated around the linker between the TTF and PPD molecules.