TCNQ Moieties Research Articles

In silico design of organic p–n junction diodes using quantum chemical calculations

To design suitable organic p–n junction diodes, modeling and simulation were performed for three donor–bridge–acceptor moieties using density functional theory. Three electron donor species namely TTF, DPh-BTBT and BEDT-TTF were connected to the electron acceptor TCNQ moiety through an insulating σ bridge. The low HOMO–LUMO energy gap for these modeled species indicates that there is a good semiconducting route for electron transport between donor and acceptor moieties via an insulating bridge. The electric field was applied from donor to acceptor and from acceptor to donor moieties to further investigate the possible direction of charge transport. It has been observed that the HOMO–LUMO gap shrinks when the electric field direction is from donor to acceptor species and increases when the electric field direction is from acceptor to donor moieties.

TCNQ molecular semiconductor of the Cu(II)TAAB macrocycle: Optical and electrical properties

The present study reports the doping of a semiconducting molecular material through the formation of hydrogen bonds between the macrocycle Cu(II)(TAAB) and the electronic acceptor TCNQ. According to density functional theory (DFT) calculations and electron paramagnetic resonance (EPR) analysis, the doped compound has the shape of a distorted square pyramid, with four nitrogen atoms in the equatorial position and the apical oxygen atom from the water ligands. These water molecules can generate strong hydrogen bonds with TCNQ and the TAAB metallic complex. Thin films of copper molecular material were obtained through high vacuum evaporation and were structurally characterized by IR spectroscopy, EPR and scanning electron microscopy (SEM). Additionally, the absorption coefficient (α) and photon energy (hν) were calculated from UV–vis spectroscopy and used to determine the optical activation energy in each film, from which its semiconducting behavior was established. An important aspect to consider is that the presence of hydrogen bonds is essential to establish the semiconducting nature of these species; this chemical behavior, as well as the resulting electronic mobility, have been studied by DFT theoretical calculations, which reinforce the experimental conclusion of a relationship between Cu(II)TAAB and TCNQ moieties generated by a weak bond. Finally, I–V characteristics have been obtained from a glass/ITO/doped molecular semiconductor/Ag device using Ag and ITO electrodes. Results for the copper-based device show that, at low voltages, the conduction process is of an ohmic nature while, at higher voltages, space-charge-limited current (SCLC) is found. It is highly probable that the doping effect in TCNQ favors electronic transport due to the formation of conduction channels caused by dopant-favored anisotropy.

TCNQ-embedded heptacene and nonacene: synthesis, characterization and physical properties

Incorporation of 7,7,8,8-tetracyanoquinodimethane (TCNQ) moieties into the acene backbone has been successfully achieved and two heptacene-TCNQ derivatives and one nonacene-TCNQ derivative have been synthesized and well characterized. Two TCNQ moieties have been embedded into heptacene and nonacene backbones for the first time. All the three compounds have good stability and solubility due to the presence of TCNQ moieties. Single crystal analysis revealed a bent butterfly-like conformation of these molecules. Their charge transport properties have been characterized using organic field effect transistors (OFETs).

The origin of the strong interfacial charge-transfer absorption in the surface complex between TiO2 and dicyanomethylene compounds

Interfacial charge transfer transitions between organic and inorganic materials are expected to be a potential photoinduced charge separation mechanism for photoenergy conversions. Recently, we reported that the hybrid material formed from TiO2 nanoparticles and an organic electron acceptor, 7,7,8,8-tetracyanoquinodimethane (TCNQ), shows strong interfacial charge transfer absorption in the visible region. In this work, we have theoretically studied the structure, and electronic and absorption properties in order to clarify the formation mechanism and the origin of the strong interfacial charge transfer absorption. Density functional theory (DFT) calculations employing an anatase Ti14O28H2(OH)2(H2O)2 nano-cluster unraveled that the surface complex is formed by a nucleophilic addition reaction between a surface hydroxyl group of TiO2 and the carbon atom of the methylene moiety in TCNQ with the drastic changes in the structure and electronic properties of TCNQ. In the formation process, owing to the high electron affinity of TCNQ, a negative charge of the surface oxygen atom is transferred to the TCNQ moiety. This leads to a significant electronic hybridization between TiO2 and TCNQ, which is the origin of interfacial charge transfer transitions.

Synthesis and Structural Characterization of a TCNQ Based Organic Semi-Conducting Material with a 2:5 Stoichiometry

The tetrabutylammonium complex with a 2:5 stoichiometry, (n-Bu(4)N)(2)(TCNQ)(5), has been prepared and structurally characterized by X-ray crystallography. Diagnostic bands in the Raman spectrum and signature features in the electrochemistry confirm that the TCNQ moieties are partially charged in the solid state. EPR, magnetic susceptibility, and electrical conductivity measurements are all consistent with (n-Bu(4)N)(2)(TCNQ)(5) behaving as a quasi-one-dimensional organic semiconductor.

Application of Alkyne‐TCNQ Addition Reaction to Polymerization

The polymerization using a high-yielding addition reaction between electron-rich alkynes and 7,7,8,8-tetracyanoquinodimethane (TCNQ) derivatives is described. The bifunctional monomer containing two TCNQ moieties and the counter comonomer bearing two dialkylaniline (DAA)-substituted alkynes are reacted in 1,2-dichloroethane under mild heating conditions. At the high monomer concentrations, high molecular weight linear polymers are obtained, while the reaction at the low monomer concentrations produces a significant amount of the cyclic compounds. A clear relationship between the monomer concentration and the cyclic compound amount is demonstrated. The obtained polymers feature a sufficient thermal stability with the decomposition temperature exceeding 300 °C as well as strong charge-transfer (CT) bands and redox activities ascribed to the produced donor-acceptor moieties. These features are also used to optimize the polymerization conditions and to estimate the chemical structures.

Impact of Metal-Ion Dependence on the Porous and Electronic Properties of TCNQ-Dianion-Based Porous Coordination Polymers

A series of TCNQ-dianion-based porous coordination polymers [M(TCNQ)bpy] (M = Fe, Zn, Mn, Co, Cd) have been synthesized and characterized. The synthesis reactions of these compounds are promoted by the addition of ascorbic acid, which is the key to obtaining a high yield. They form almost identical three-dimensional pillared layer structures with the M-TCNQ two-dimensional layers linked by bpy pillar ligands. The electronic properties of these compounds vary depending on the constitutional metal ions and guest molecules. We found that the electronic interaction between metal ions and TCNQ moieties in the frameworks strongly impacted the electronic properties of the compounds.

Long-Range Ordered Magnet of a Charge-Transfer Ru24+/TCNQ Two-Dimensional Network Compound

Two isostructural 2D assemblies composed of [Ru2(O2CCF3)4] and TCNQ or TCNQF4 in a 2:1 ratio were synthesized: [{Ru2(O2CCF3)4}2TCNQ].3(p-xylene) (1b) and [{Ru2(O2CCF3)4}2TCNQF4].3(p-xylene) (2). In 1b, the TCNQ moiety is assigned to be neutral because of no significant electron transfer from the Ru24+ units. Therefore, the magnetic property of 1b can be understood to be a paramagnetic nature of the isolated Ru24+ unit, while, a fully charge-transfer from the Ru2 units to the TCNQF4 molecules in 2 leads to charge delocalization spreading over the 2D network and allows a long-range magnetic order to occur. On the basis of an idea of the resonance scheme in charge-transfer D2A network systems, the first successful example of a charge-transferred magnet in the Ru2-TCNQ system was rationally designed by tuning redox between [Ru2]4+ and the TCNQ molecule changing from TCNQ to TCNQF4.

A Rigid Neutral Molecule Involving TTF and TCNQ Moieties with Intrinsic Charge‐ and Electron‐Transfer Properties that Depend on the Polarity of the Solvent

A Rigid Neutral Molecule Involving TTF and TCNQ Moieties with Intrinsic Charge‐ and Electron‐Transfer Properties that Depend on the Polarity of the Solvent

A Rigid Neutral Molecule Involving TTF and TCNQ Moieties with Intrinsic Charge‐ and Electron‐Transfer Properties that Depend on the Polarity of the Solvent

A Rigid Neutral Molecule Involving TTF and TCNQ Moieties with Intrinsic Charge‐ and Electron‐Transfer Properties that Depend on the Polarity of the Solvent

Thin films of hydroxy-TEMPO-substituted TTF and of its charge-transfer complex with TCNQ

Thin films of 4-hydroxy-TEMPO-substituted TTF [TTF-(OH)TEMPO] were grown on ex situ cleaved KBr (001) using the high vacuum evaporation technique. Sub-micronic grains uniformly covering the KBr surface were evidenced by scanning electron microscopy (SEM). The films were also studied by infrared (IR), electron spin resonance spectroscopy (ESR) and X-ray photoelectron spectroscopy (XPS). Amorphous thin films of [TTF-(OH)TEMPO][TCNQ] were obtained on KBr pellets and on micro-rough Si(001) wafers using chemical vapour deposition (CVD). They were characterized by SEM, IR, XPS and ESR. SEM images on micro-rough Si(001) wafers evidenced micro-needles (0.5–2 μm in length, 0.1–0.2 μm in diameter), uniformly covering the substrate surface. CN stretching frequencies were in agreement with a reduced TCNQ moiety, thus indicating a charge transfer between the donor [TTF-(OH)TEMPO] and the acceptor (TCNQ) molecules (degree of charge transfer ∼1).

Crystal and Molecular Structures of 2-Dodecyl-7,7,8,8-tetracyanoquinodimethane

Abstract To develop a possible structural model for molecular arrangement in Langmuir–Blodgett (LB) films of 2-alkyl-7,7,8,8-tetracyanoquinodimethane (alkyl-TCNQ) the molecular and crystal structures of 2-dodecyl-7,7,8,8-tetracyanoquinodimethane (dodecyl-TCNQ) have been determined by X-ray single-crystal analysis. The compound crystallizes in the triclinic space group P1- with Z = 2. The molecule consists of the planar TCNQ moiety and the dodecyl chain having all-trans conformation. In the crystals the TCNQ fragments make a stacking structure in a head-to-head manner across the centers of symmetry to form a double layer of TCNQ groups. The dodecyl chains protrude oppositely from the TCNQ layers and are assembled to form a close-packed layer, being interdigitated with each other. In this way, the TCNQ moieties and the dodecyl groups form layers alternately. This molecular arrangement in the crystal provides new insight into the structure of the LB films of alkyl-TCNQ.

Hybrid Langmuir–Blodgett films of APT and cyanine with binary output modes

Hybrid Langmuir–Blodgett (LB) films were fabricated by transferring pure monolayers of an azobenzene derivative having a TCNQ (7,7,8,8-tetracyanoquinodimethane) moiety (APT) and then 1:1 mixed monolayers of cyanine/APT on solid substrates. The hybrid LB films have binary output modes. The alternate irradiation of UV and visible light yielded reversible cis- trans isomerization of APT, which was accompanied by the electrical conductivity switching associated with APT molecules and the change in the optical properties of the films due to the development of the J-band of the cyanine dye (CY). The order of the sequential deposition of the APT pure monolayers and the 1:1 mixed monolayers of CY/APT plays an important role in realizing the hybrid LB films with binary output modes.

Chemistry of the Ag(2)(dmb)(2)(2+) Template (dmb = 1,8-Diisocyano-p-menthane). Preparation, Characterization, and X-ray Structures of the Ag(2)(dmb)(2)Y(2) Dimers (Y = NO(3)(-), ClO(4)(-), CH(3)CO(2)(-)) and the Paramagnetic [Ag(4)(dmb)(4)(TCNQ)(3)]TCNQ Complex (TCNQ = 7,7,8,8-Tetracyanoquinodimethane).

Direct reactions of the AgY salts with dmb (1,8-diisocyano-p-menthane) in a 1:1 stoichiometric amount generate the binuclear Ag(2)(dmb)(2)Y(2) complexes. The X-ray crystallography establishes that the structure consists of two Ag(+) atoms bridged by two dmb ligands forming a 20-membered ring and by two counteranions via one of the O-atoms, forming a four-membered ring (local symmetry = D(2)(h)()). The Ag(I).Ag(I) separations are 3.909(1) and 3.6831(8) Å for Y = NO(3)(-) and CH(3)CO(2)(-), respectively. Reactions of Ag(2)(dmb)(2)Y(2) (Y = NO(3)(-), ClO(4)(-)) with LiTCNQ lead to the paramagnetic tetranuclear species [Ag(4)(dmb)(4)(TCNQ)(3)]TCNQ. The structure at 180 K consists of two Ag(2)(dmb)(2)(2+) species (d(Ag.Ag) = 4.113(1) Å held together by three parallel TCNQ(-)'s, with Ag(+).N&tbd1;C distances ranging from 2.359(5) to 2.787(5) Å. Two of the Ag(+) atoms are tricoordinated, and the other two are tetracoordinated placed within in a centrosymmetric geometry. The three bridging TCNQ(-)'s exhibit interplanar distances of 3.333(1) Å, and the Ag(4) species are packed side-by-side with two adjacent TCNQ(-)'s face-to-face (separation = 3.372(1) Å) forming an infinite pi-stacked chain TCNQ(-)'s. The TCNQ(-) counteranion also exhibits weak pi-contacts via the -CN groups with other counteranions. The magnetic susceptibilities, EPR spectra, and unit cell parameters have been measured as a function of temperature. The magnetic data are best explained by extended chains of antiferromagnetically coupled S = (3)/(2) and S = (1)/(2) centers for the [Ag(4)(dmb)(4)(TCNQ)(3)](+) and TCNQ(-) moieties, respectively. No hyperfine structure has been observed between 106 and 290 K, indicating the presence of rapid exchange in the paramagnetic system. Crystal data: Ag(2)(dmb)(2)(NO(3))(2), crystal system, orthorhombic, space group = C(cmb), a = 8.6464(15) Å, b = 16.375(3) Å, c = 20.663(5) Å, Z = 4; Ag(2)(dmb)(2)(O(2)CCH(3))(2).2H(2)O, crystal system triclinic, space group P&onemacr;, a = 9.1175(9) Å, b = 9.1451(10) Å, c = 11.7247(8) Å, alpha = 80.294(7) degrees, beta = 71.124(7) degrees, gamma = 64.258(8) degrees, Z = 1; [Ag(4)(dmb)(4)(TCNQ)(3)]TCNQ, crystal system triclinic, space group = P&onemacr;, a = 9.9837(12) Å, b = 13.5194(14) Å, c = 17.1788(9) Å, alpha = 99.423(6) degrees, beta = 101.512(8) degrees, gamma = 96.917(11) degrees, Z = 1.

The synthesis, solid state conductivity and X-ray crystal structure of [Fe{ η5-C 5H 5)( E- η5-C 5H 4–CHCH-9-C 16H 9)][1,4-{(CN) 2C} 2C 6H 4

The new compounds [Fe( η 5-C 5H 5)( E- η 5-C 5H 4–CHCH-9-C 16H 9)], [Fe( η 5-C 5H 5)( E- η 5-C 5H 4–CHCH-9-C 16H 9)][(CN) 2CC(CN) 2] and [Fe( η 5-C 5H 5)( E- η 5C 5H 4–CHCH-9-C 16H 9)][1,4-{(CN) 2C} 2C 6H 4] have been synthesized and characterized by their mass, IR and 1H NMR spectra. The crystal structure of the latter compound contains 1,2-ferrocenyl-pyrenyl-ethene and 1,4-{(CN) 2C} 2C 6H 4 (TCNQ) molecules alternating in stacks characteristic of π– π* electron donor–acceptor complexes. The pyrene and TCNQ moieties are nearly parallel, angle of tilt 5.3°, with interplanar separations of 3.33 and 3.42 Å. Microwave cavity perturbation measurements have been used to show that this solid behaves as a normal semi-conductor below 176 K.

Reactivity of tungsten(V) mononuclear complexes towards Li(TCNQ) and TCNQ. Comparison of the crystal structures of [W(S2CNMe2)4][TCNQ] and [Mo(S2CNMe2)4][TCNQ]·MeCN (TCNQ = 7,7,8,8-tetracyanoquinodimethane)‡

The reaction of tungsten(V) complexes [W(S2CNR2)4]I (R = Me or Et) with Li(TCNQ) in a dimethylformamide–water mixture at room temperature afforded the new derivatives [W(S2CNR2)4][TCNQ] 1a and 1b (TCNQ = 7,7,8,8-tetracyanoquinodimethane). These compounds reacted further with TCNQ in acetonitrile to produce [W(S2CNR2)4][TCNQ]2 in which the TCNQ moieties are in a mixed-valence state. The physical properties of these new derivatives in solution and in the solid state are presented. The structures of 1a and of its molybdenum analogue [Mo(S2CNR2)4][TCNQ]·MeCN 2a have been studied by X-ray diffraction analyses: in 1a the TCNQ moieties form alternating stacks along the c axis according to a quite unusual bond–bond overlap; in 2a the TCNQ˙– moieties are dimerized and exhibit the usual slipped conformation.

Influence of Benzoannulation on the Molecular and Electronic Structures of Tetracyanoquinodimethanes

The molecular and electronic structures of TCNQ and its π-extended derivatives benzo-TCNQ and TCAQ have been investigated using the semiempirical PM3 method and ab initio 6-31G* calculations. The steric hindrance introduced by lateral benzoannulation determines the loss of planarity of the TCNQ moiety for benzo-TCNQ and TCAQ. For both molecules, the most stable conformation corresponds to a butterfly-type structure, in which the TCNQ ring adopts a boat conformation and the lateral benzene rings remain planar. This structure lies, at the 6-31G* level, 33.45 kcal/mol below the fully planar conformation and 17.50 kcal/mol below a second local minimum for TCAQ, while it only lies 3.35 kcal/mol below the planar structure for benzo-TCNQ. The geometries of the anions and dianions have been also optimized at the semiempirical and ab initio levels. Although reduction induces the aromatization of the TCNQ moiety, the anions of benzo-TCNQ and TCAQ remain nonplanar. The stability of the anions with respect to the neutral systems is thus calculated to decrease along the series TCNQ > benzo-TCNQ > TCAQ, thus explaining the decrease of the electron-acceptor properties along this series. For the dianions, the polycyclic skeleton is fully planar and the C(CN)2 groups are twisted out of the molecular plane. While the first two extra electrons are mostly incorporated into the C(CN)2 groups, the third electron added to form the trianion is shown to enter the central polyacenic unit for TCAQ. This result explains the formation of relatively stable trianions and tetraanions for TCAQ. PM3 calculations have been especially useful in characterizing the stationary structures located for each compound and have been used as a guide for 6-31G* calculations. PM3-optimized geometries are in good agreement with experimental X-ray data and 6-31G* results.

Reduction of TCNQ in Mixed Monolayers with Cationic Amphiphiles at the Air/Water Interface

Investigations of the molecular organization characteristics of octadecyltetracyanoquinodimethane (C18TCNQ) in mixed monolayers with cationic amphiphiles such as dioctadecyldimethylammonium bromide (DOMA) has revealed that the TCNQ moiety is spontaneously reduced at the air/water interface. The reduced TCNQ molecules react further with oxygen resulting in the formation of decay products. No such reduction is observed either in pure C18TCNQ monolayers or in mixed monolayers with lipids having neutral or negatively charged head groups. The reduction process depends on the molecular composition (molar ratio of DOMA and C18TCNQ in the mixed monolayer), subphase pH (e.g. no reduction at pH 2), and the nature (e.g. no reduction in the presence of ClO 4 - ) and concentration of co-counterions in the subphase. The reduction process and the molecular organization characteristics have been studied using surface pressure- and surface potential-area isotherms and surface enhanced UV-vis reflection spectroscopy. The results are discussed in terms of interfacial pH, dielectric constant, and the redox potential of electroactive species at the air/water interface

Determination of charge transfer in molybdenum complexes of 7,7,8,8-tetracyano-p-quinodimethane with vibrational spectroscopy

Abstract The influence of charge transfer on the vibrational lines of three new molybdenum TCNQ complexes [MoO(dtc)3](TCNQ) 1a, [Mo(dtc)4](TCNQ) 2a, and [Mo(dtc)4](TCNQ)2 3a is reported (dtc=Et2NCS2). It is shown that Raman scattering is able to probe the charge state of TCNQ entities in these complexes. Infrared spectra are discussed and compared to Raman spectra. Electronic polarization of the TCNQ moieties and reduction of TCNQ° in TCNQ•− is found for all complexes. The estimated charge transferred when reduction occurs is one electron onto the TCNQ molecule whereas it is about 0.2–0.3 electron onto nitrile groups. The formation of monomers and dimers of TCNQ in these complexes is discussed in relation with specific Raman lines found in reference compounds such as TCNQ salts of alkali. These new Raman data suggest to us that TCNQ moieties form mainly dimers and monomers in complexes 1a and 2a, respectively.

Infrared studies of VINφ 2(TCNQ) 2 salt with two different TCNQ stacks

VINφ 2(TCNQ) 2 salt with two different one-dimensional TCNQ columns is characterized by an electron and vibrational spectroscopy (IR absorption, polarized reflection and Raman scattering). Anisotropy of the optical conductivity, origin and nature of the electron-molecular vibration coupling and charge distribution on the TCNQ moieties of the salt are discussed.