TTF TCNQ Research Articles

Volumetric Electron Transfer from Metabolites to Chemically Doped Polymer Electrodes

AbstractThe development of sensor electrode materials for the detection of metabolites will enable point‐of‐care diagnostic devices for the monitoring and treatment of metabolic diseases such as diabetes. Current state‐of‐the‐art glucose sensing electrodes employ the organic salt tetrathiafulvene tetracyanoquinodimethane (TTF TCNQ) to receive electrons directly from enzymatic reactions of glucose. However, TTF TCNQ is insoluble in most solvents, making it challenging to deposit high‐quality electrodes. Furthermore, its hydrophobicity hinders its interface with aqueous solutions in physiological environments. To overcome these issues, TCNQ derivatives are introduced into an electron‐rich and hydrophilic conjugated polymer. Thus, a polymeric electrode is demonstrated that is easily solution processible and can undergo volumetric direct electron transfer with glucose reactions throughout its bulk. This study further elucidates the electron transfer mechanism during chemical doping and metabolite sensing reactions to inform general design rules for this new class of glucose sensing materials.

Charge-transfer complex promotes energy storage performance of single-moiety organic electrode materials in aqueous zinc-ion battery at low temperatures

Charge-transfer organic materials are molecular metallic materials with high electronic conductivity, but their potential in rechargeable batteries, especially at low temperatures, has not been investigated. In this work, micro-structured organic charge-transfer complex tetrathiofluorene-7,7,8,8-tetroquinolinedimethane (TTF-TCNQ) is applied as cathode material in aqueous zinc-ion batteries (AZIBs). Ionic storage behavior of TTF–TCNQ complex is systematically investigated from 25 ℃ to −40 ℃. Owing to higher electrical conductivity and higher ionic diffusivity in ionic storage, smaller charge transfer resistance, and lower activation energy, TTF-TCNQ shows much superior rate and cycling performance than each single-moiety counterpart, especially at low temperatures. Reaction mechanism is explored by ex-situ X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier Transform infrared spectroscopy (FT-IR) and in-situ Raman technologies, confirming that CN and CS groups are the redox centers and the redox reaction is highly reversible. Our research not only provides a new type of choice for AZIBs at low temperatures, but also greatly broads the application field of charge-transfer complexes.

Cytochrome P450 2D6 biosensor for perphenazine based on multi-walled carbon nanotube/ionic liquid and tetrathiafulvalene-tetracyanoquinodimethane salt/ionic liquid gels

A cytochrome P450 2D6 (CYP2D6) biosensor was developed with the incorporation of multi-walled carbon nanotube/ionic liquid and tetrathiafulvalene-tetracyanoquinodimethane salt/ionic liquid (MWNT/IL-[TTF–TCNQ]/IL) gels. The MWNT/IL-[TTF–TCNQ]/IL gels were characterized using Fourier-transform infrared spectroscopy, ultraviolet–visible spectroscopy, and scanning electron microscopy. Utilizing the excellent stability of the MWNT/IL gel and the unique structure of the [TTF–TCNQ]/IL gel, CYP2D6 was immobilized on the screen-printed electrode with high bioactivity. Moreover, the CYP2D6 catalytic effect was highly promoted upon application of MWNT/IL-[TTF–TCNQ]/IL gels as the mediating system. The proposed MWNT/IL-[TTF–TCNQ]/IL gel-based CYP2D6 biosensor was used to detect perphenazine via voltammetry and amperometry. The calibration of perphenazine ranged from 6 × 10−8 to 1.6 × 10−5 M with a detection limit of 2.05 × 10−8 M. It is expected that the MWNT/IL-[TTF–TCNQ]/IL gel-based CYP2D6 biosensor opens new avenues for promising advances in the analysis of drugs.

A TTF–TCNQ complex: an organic charge-transfer system with extraordinary electromagnetic response behavior

Charge-transfer based molecular conductors have attracted great attention in recent years, but have been rarely explored in the field of electromagnetic materials.

Understanding the Charge Transfer at the Interface of Electron Donors and Acceptors: TTF-TCNQ as an Example.

Charge transfer between an electron donor and an electron acceptor is widely accepted as being independent of their relative configurations if the interaction between them is weak; however, the limit of this concept for an interacting system has not yet been well established. Our study of prototypical electron donor-acceptor molecules, tetrathiafulvalene-tetracyanoquinodimethane, using density functional theory based on an advanced functional, clearly demonstrates that for interacting molecules, their configurational arrangement is as important as their individual electronic properties in the asymptotic limit to determine the charge transfer direction. For the first time, we demonstrate that by changing their relative orientation, one can reverse the charge transfer direction of the pair, causing the molecules to exchange roles as donor and acceptor. Our theory has important implications for understanding the interfacial charge-transfer mechanism of hybrid systems and related phenomena.

Discrimination of alkyl and aromatic amine vapors using TTF-TCNQ based chemiresistive sensors.

We report a chemiresistive sensor approach based on a TTF-TCNQ charge transfer material, which can real-time detect and distinguish the vapors of alkyl amine and aromatic amine species under ambient conditions, based on the dramatic difference in the kinetics of the electric current recovery processes after the exposure of the two amine species.

Built-in TTF–TCNQ charge-transfer salts in π-stacked pillared layer frameworks

A TTF–TCNQ charge-transfer salt was incorporated in a layer structure with paddlewheel-type carboxylate-bridged dirhodium(II, II) complexes ([Rh2]) to construct π-stacked pillared layer frameworks of formula (TTF)n[{Rh}2(TCNQ)] (n = 1 or 2).

Fabrication of Conducting Thin Films on the Surfaces of 7,7,8,8-Tetracyanoquinodimethane Single-Component and Charge-Transfer Complex Single Crystals: Nucleation, Crystal Growth, Morphology, and Charge Transport

Electrically conducting TTF–TCNQ thin films are fabricated on various molecular crystals containing 7,7,8,8-tetracyanoquinodimethane (TCNQ) by exposing a tetrathiafulvalene (TTF) vapor under ambient conditions. To systematically investigate the properties of the films, mixed-stack TCNQ charge-transfer (CT) complex crystals with nine kinds of donors have been prepared as the substrates, and the morphology change of the films on the surfaces at the initial stage of the TTF vapor contact has been observed. When the substrate is a TCNQ single-component crystal, randomly oriented TTF–TCNQ nanometer-size needle crystals are grown by the reaction with a TTF vapor. However, when the substrate is a TCNQ CT complex crystal, TTF–TCNQ crystals are grown with alignment of their needle axis along the mixed-stack direction of the substrate. The surface roughness, the size of the needle crystals, and the degree of the dense packing of the needles have been found to systematically depend on the strength of the CT interact...

Opposites Attract: Organic Charge Transfer Salts

A laboratory experiment is described that introduces second-year undergraduate organic chemistry students to organic electronic materials. The discovery of metallic conductivity in the charge transfer salt tetrathiafulvalene tetracyanoquinodimethane (TTF–TCNQ) is a landmark result in the history of organic electronics. The charge transfer interaction is not only relevant to real-world applications, it also has pedagogical value related to understanding redox chemistry, aromaticity, and conjugation. In this laboratory experiment, students carry out a solution phase synthesis of TTF–TCNQ from the molecular precursors TTF and TCNQ. The product is characterized by infrared spectroscopy. Characteristic changes in absorption frequency are correlated with increased aromatic character and observable lengthening of the nitrile bond. In an optional extension, students experimentally verify the great difference in conductivity between the charge transfer salt and the neutral parent components.

Polyaniline/carbon nanofiber and organic charge transfer complex based composite electrode for electroanalytical urea detection

A composite electrode based on polyaniline coated modified carbon nanofiber (PANI–mCNF), tetrathiafulvalene–tetracyanoquinodimethane (TTF–TCNQ) and urease (Ur) enzyme was evaluated as biosensor for urea detection. Homogeneous coating of PANI on the surface of mCNF was achieved by oxidative polymerization of anilium ion. Fourier transform infrared (FTIR) spectroscopy and field-emission scanning electron microscopy (FESEM) were used to analyze the structural and morphological characteristics of PANI–mCNF nanocomposite. The biosensor showed excellent electroactivity in neutral and basic medium. A linear response to urea in the concentration range of 0.5–8.4 mM with a correlation coefficient of 0.998, good sensitivity (2.84 µA cm−2 mM−1) and a fast response time (ca. 4 s) was obtained for the biosensor. The minimum detection limit was found to be 3 µM. The biosensor was stable and showed minimal loss in sensitivity, even after two months of storage. The amalgamation of the PANI and CNF synergistically enhances the performance of the biosensor for electroanalytical detection of urea.

Highly ordered alignment of conducting nano-crystallites on organic semiconductor single crystal surfaces

A conducting thin layer of aligned fibrous nano-crystallites of tetrathiafulvalene–7,7,8,8,-tetracyanoquinodimethane (TTF–TCNQ) is fabricated directly on semiconducting organic crystals under ambient conditions. The widths of the crystallites are 50–100nm. Their growth direction is governed by the direction of the intermolecular charge transfer interactions in the substrate crystal. The carrier transport in the film is metallic between 150K and 300K, reflecting the uniform alignment of the TTF–TCNQ nano-crystallites on the substrate crystal.

Charge-transfer complexes: new perspectives on an old class of compounds

The discovery of the organic metal TTF–TCNQ in 1973 led to an explosion of research conducted on organic charge-transfer complexes. While these materials have been studied intensely for several decades, the research was mostly aimed at the discovery of materials with high room-temperature conductivity or high-temperature superconductivity. Recently, attention has turned to technologically-relevant properties of charge-transfer complexes, such as ambipolar transport, metallicity, photoconductivity, ferroelectricity or magnetoresistance. This manuscript reviews the growth, structure and properties of charge-transfer complexes and underlines recent progress in their application in organic devices. Their prospects in future applications are discussed, as well as the challenges yet to be overcome to understand the fundamental parameters governing their operation.

An inkjet-printed TTF–TCNQ nanoweb as an effective modification layer for high mobility organic field-effect transistors

The interface between an organic semiconductor and a dielectric plays an important role in determining the device performance of organic field-effect transistors (OFETs). A uniform ink-jet printed tetrathiafulvalene–tetracyanoquinodimethane (TTF–TCNQ) nanoweb was investigated as the buffer layer between the semiconductor layer and the dielectric in OFETs. Compared to the n-octadecyl triethoxysilane (OTS) modification layer, we observed an increase in the “effective” field effect mobility by as much as several tens of times while maintaining the high on/off ratios in the TTF–TCNQ based device. This work demonstrated that with the advantages of low-cost, high-performance and printability, the TTF–TCNQ nanoweb could serve as an excellent buffer layer for OFETs.

Colloidal Solutions of Organic Conductive Nanoparticles

Although molecular metals have been known for decades, their insolubility, low vapor pressure, and synthesis routes have prevented them from being integrated into electronic devices. We have prepared stable colloidal solutions of the organic metal TTF-TCNQ that overcome such difficulties. The solutions contain well-dispersed nanoparticles stabilized by long alkyl chain amines. They afford soluble powders by evaporation and homogeneous thin films by drop-casting. Powders and films show room temperature conductivities in the 0.01-0.1 S cm(-1) range.

Acetylcholinesterase biosensor for carbamate drugs based on tetrathiafulvalene–tetracyanoquinodimethane/ionic liquid conductive gels

A highly sensitive acetylcholinesterase biosensor was developed for detection of carbamate drugs based on TTF–TCNQ–ionic liquid gel thiocholine sensor. The TTF–TCNQ–ionic/ionic liquid gel was characterized by FT-IR and scanning electron microscopy. The electrocatalytic behavior of TTF–TCNQ–ionic liquid gels toward oxidation of thiocholine was thoroughly investigated. 1-Ethyl-3-methylimidazolium tetracyanoborate gel based sensor allowed amperometric detection of thiocholine at +400mV vs. Ag/AgCl with a high sensitivity of 55.9±1.2μAmM−1cm−2 and a low detection limit equal to 7.6μM. The catalytic rate constant and diffusion constant of thiocholine were estimated from chronoamperometric data. The proposed biosensor based on AChE immobilized in sol–gel matrix was used for the detection of two carbamate therapeutic drugs. Very low detection limits of 26pM eserine and 0.3nM neostigmine were achieved. The analysis of spiked tap water proved the biosensor capability to be used as a screening method for detection of carbamate drugs in wastewaters.

Alternating electron transfer mechanism in the case of high-performance tetrathiafulvalene–tetracyanoquinodimethane enzymatic electrodes

The electron transfer mechanism in enzymatic electrodes employing tetrathiafulvalene–tetracyanoquinodimethane (TTF–TCNQ) complex is despite of numerous publications, still a matter of controversy. To clarify this issue, enzymatic electrodes based on TTF, TCNQ and TTF–TCNQ have been prepared in an identical manner and their electrochemical behavior and activity have been tested. The enzymatic electrodes containing the respective mediator, glucose oxidase and Vulcan nanoparticles dispersed in a gelatin matrix show high activity for glucose oxidation in terms of both currents and oxidation onset potential. The observed electrochemical features, supported by infrared spectroscopy measurements, indicate that the activity of the TTF–TCNQ electrodes can be ascribed to TTF and TCNQ species released from the organic salt. The two mediators are active in different potential regions, implying an alternating electron transfer mechanism. TTF is active at more negative potentials and generates higher current densities, while TCNQ exhibits activity only at potentials more positive than 0V vs. SCE. This work analyzes and summarizes different aspects of the most recent electron transfer hypotheses by providing the respective experimental evidences in an effort for better understanding of this puzzling bioelectrochemical system.

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.

Influence of irradiation-induced disorder on the Peierls transition in TTF–TCNQ microdomains

The combined influence of electron irradiation-induced defects, substrate-induced strain and finite size effects on the electronic transport properties of individual micron-sized thin film growth domains of the organic charge transfer compound tetrathiafulvalene– tetracyanoquinodimethane (TTF–TCNQ) have been studied. The TTF–TCNQ domains have been isolated and electrically contacted by focused ion beam etching and focused ion and electron-beam-induced deposition, respectively. This allowed us to measure the temperature-dependent resistivity and the current–voltage characteristics of individual domains. The dependence of the resistivity on temperature follows a variable-range hopping behaviour which shows a crossover of the exponents as the Peierls transition is approached. The low temperature behaviour is analysed within the segmented rod model of Fogler, Teber and Shklovskii which was developed for charge-ordered quasi one-dimensional electron crystals (Fogler et al 2004 Phys. Rev. B 69 035413). The effect of substrate-induced biaxial strain on the Peierls transition temperature is discussed with regard to its interplay with the defect-induced changes.

Direct hybrid glucose–oxygen enzymatic fuel cell based on tetrathiafulvalene–tetracyanoquinodimethane charge transfer complex as anodic mediator

TTF–TCNQ has been used for the first time as a mediator in a direct glucose fuel cell operating on gas-phase oxygen. It has been shown that TTF–TCNQ forms highly irregular porous structure, which emphasizes the importance of optimization of mass transport and kinetic resistance in the catalyst layer. Kinetics resistance can be optimized by variation of the mediator and/or enzyme loading, while mass transport resistance mainly by the variation of other structural parameters such as electrode thickness. The optimized anode reached limiting current densities of nearly 400 μA cm −2 in presence of 5 mM glucose under rotation. The enzymatic fuel cell exhibited unexpectedly high OCV values (up to 0.99 V), which were tentatively ascribed to different pH conditions at the anode and the cathode. OCV was influenced by glucose crossover and was decreasing with an increase of glucose concentration or flow rate. Although the performance of the fuel cell is limited by the enzymatic anode, the long-term stability of the fuel cell is mainly influenced by the Pt cathode, while the enzymatic anode has higher stability. The fuel cell delivered power densities up to 120 μW cm −2 in presence of 5 mM glucose, depending on the glucose flow rate.

Defect-induced shift of the Peierls transition in TTF–TCNQ thin films

In this paper we investigate the influence of the substrate material and film thickness on the Peierls transition temperature in tetrathiafulvalene–tetracyanoquinodimethane (TTF–TCNQ) thin films, grown by physical vapor deposition. Our analysis shows that the substrate material and the growth conditions strongly influence the film morphology. In particular, we demonstrate that the Peierls transition temperature in thin films is lower than in TTF–TCNQ single crystals. We argue that this effect arises due to defects, which emerge in TTF–TCNQ thin films during the growth process.