Tetracyanoethylene Research Articles

Synthesis of Nonplanar Push-Pull Chromophores with Various Heterocyclic Moieties via [2 + 2] Cycloaddition-Retroelectrocyclization Reaction.

A series of 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) derivatives with various heterocyclic moieties, including pyridine, carbazole, indole, and benzothiadiazole, was newly synthesized through a [2 + 2] cycloaddition-retroelectrocyclization reaction. Symmetric electron-rich 1,3-butadiynes with end-capped heterocyclic substituents were reacted with tetracyanoethylene (TCNE), yielding the target TCBD products in 60-80% yields under ambient or mild heating conditions. The thermal stability and optical and electrochemical properties of both 1,3-butadiyne precursors and the corresponding TCBD derivatives were investigated by using thermogravimetric analysis (TGA), UV-vis spectroscopy, and cyclic voltammetry (CV). The TCBD derivatives featured narrow bandgaps due to the intramolecular charge transfer interactions of push-pull chromophores. In addition, the optimized structures and frontier molecular orbitals with their energy levels were determined by density functional theory (DFT) calculations.

A focus on microporous perovskites: new tricks for an old dog.

Hybrid organic-inorganic perovskites (HOIPs) are widely studied for their potential in optoelectronic devices due to their unique semiconductor features. Porous HOIPs are extremely rare, with (APOSS)[CuCl4]4 being one of the very few examples, featuring 12 Å pores within its lattice. Reed and coworkers (C. W. Dalton, P. M. Gannon, W. Kaminsky and D. A. Reed, Chem. Sci., 2025, DOI: https://doi.org/10.1039/D4SC04378B) have recently shed light on the structure of this interesting material and demonstrated that these pores can incorporate large electroactive molecules such as ferrocene (Fc) and tetracyanoethylene (TCNE). Further, they showed that the ability to incorporate molecules within the pores also enables the synthesis of new crystalline phases and unlocks numerous applications, including gas sensing and photocatalysis, among others.

Tetracyanoethylene Na+/K+ radical anion coordination sites unveiled via electronic and vibrational fingerprints

Tetracyanoethylene (TCNE) is a very effective electron acceptor and can form stable complexes with various chemical species and is known for its interesting electronic and optical properties. The formation of the monoanion gives TCNE unique electronic and chemical properties, making it a material of interest for several technological applications including solar cells, organic battery electrodes, sodium/potassium-ion batteries and information storage devices. The chemico-physical characterization of Na+ and K+ coordination of TCNE in solution is not available so far, although it would be valuable for understanding the molecular mechanisms of charging and discharging processes in innovative battery devices. The present theoretical-computational study characterizes the vibrational and electronic properties of ion-coordinated TCNE in solution. We analyzed the ground electronic state through equilibrium structures, focusing on structural features, stability, optical properties and Raman vibrational modes. The Na+ and K+ cations, coordinated at two distinct sites, significantly alter the geometry, and modulate electronic and vibrational properties. Using ab initio molecular dynamics simulations, we computed vibrational spectra, finding that TCNE complexes serve as effective probes for detecting environmental variations, with key vibrational modes on CC and CN moieties being sensitive to cation interactions. Additionally, a correlation between C=C bond distances and vibrational frequencies was observed. In conclusion, this study provides further insight into the role of TCNE in optoelectronic applications and nonaqueous battery systems.

Impact of tetracyanoethylene plasticizer on PEO based solid polymer electrolytes for improved ionic conductivity and solid-state lithium-ion battery performance

Poly(ethylene oxide) is a promising material for solid-state lithium batteries due to its safety, ease of processing, and compatibility with lithium. However, conventional linear PEO falls short of practical requirements due to its limited ionic conductivity, a consequence of the high crystallinity of its ethylene oxide chains. This crystallinity hinders the movement of lithium ions, limiting its performance in solid-state battery applications. In this study, we successfully prepared the plasticized solid polymer electrolytes (PSPEs) based on poly(ethylene oxide) (PEO)/tetracyanoethylene (TCE) complexed with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt and studied the effect of TCE on structural, mechanical, electrical and electrochemical properties of PSPEs. The addition of tetracyanoethylene effectively disrupts the crystallinity of the PEO matrix, as confirmed by X-ray diffraction analysis. The addition of TCE also enhanced the elongation-at-break of the PEO12-LiTFSI system, indicating improved flexibility. Consequently, the ionic conductivity of the SPEs increases with increasing tetracyanoethylene content, reaching a maximum of 1.14 × 10−4 S/cm at 25 °C for the electrolyte containing 30 wt% of tetracyanoethylene. Furthermore, the plasticized SPEs exhibit a wide electrochemical stability window, as determined by linear sweep voltammetry. Solid-state battery tests demonstrate a high initial discharge capacity of 143.5 mAhg−1 at 0.1C along with good cycling performance.

Coordination Networks from [Te4]2+ Clusters and Polynitriles

AbstractThe reactions of a series of organic polynitriles with [Te4][AsF6]2 in liquid SO2 solution lead either to reduction of [Te4]2+ to elemental tellurium or to the formation of coordination polymers. With 1,3‐dicyanobenzene (1,3‐DCB), 1,4‐dicyanobenzene (1,4‐DCB), 1,2,4,5‐tetracyanobenzene (TCB), tetracyanoethylene (TCNE) and tetracyanochinodimethane (TCNQ) the coordination complexes [Te4][AsF6]2 ⋅ 2(1,3‐DCB), [Te4][AsF6]2 ⋅ 3(1,4‐DCB) ⋅ 2SO2, [Te4][AsF6]2 ⋅ TCB, [Te4][AsF6]2 ⋅ TCNE and [Te4][AsF6]2 ⋅ TCNQ ⋅ 8 SO2 were isolated and characterized by crystal structure analyses and vibrational Raman spectroscopy. The nitriles are coordinated to the square‐planar clusters forming 1D chains, 2D arrangements and 3D networks. Tetrakis(dicyanomethylene)cyclobutendiide [C4(C{CN}2)4]2− is oxidized by [Te4]2+ to the neutral cyanocarbon C4(C{CN}2)4, structurally representing a 4[radialene]. The ionization potentials and electron affinities of the cyanamide anion, cyanogen, 1,2‐DCB, 1,3‐DCB, 1,4‐DCB, TCB, C4(C{CN}2)4, TCNE and TCNQ and those polynitriles, which cause reduction of [Te4]2+, were calculated at coupled‐cluster level of theory in order to examine possible reasons for the stability of the coordination polymers based on electronic properties of the nitriles.

Formation of Carbon–Carbon Double Bond between Cp Ligand and Alkenyl Carbon of Titanacyclopentenes

AbstractReactions of bis(cyclopentadienyl)titanacyclopentenes with BiI3 gave coupling products of one Cp ligand and the alkenyl carbons in moderate yields. An NMR study of the tetracyanoethylene (TCNE) adduct of the product showed that the coupled Cp ring and the alkenyl carbons were connected by one carbon–carbon double bond. This is in sharp contrast to coupling reactions of one Cp ligand with the diene moiety in bis(cyclopentadienyl)titanacyclopentadienes, where two carbon–carbon single bonds were formed between those two components to give dihydroindenes or spiro compounds.

Reactions of Tetracyanoethylene with Aliphatic and Aromatic Amines and Hydrazines and Chemical Transformations of Tetracyanoethylene Derivatives

The significant synthetic potential and reactivity of tetracyanoethylene (TCNE) have captured the interest of numerous chemical communities. One of the most promising, readily achievable, yet least explored pathways for the reactivity of TCNE involves its interaction with arylamines. Typically, the reaction proceeds via tricyanovinylation (TCV); however, deviations from the standard chemical process have been observed in some instances. These include the formation of heterocyclic structures through tricyanovinyl intermediates, aliphatic dicarbonitriles through the cleavage of the C–C bond of a tetracyanoethyl substituent, complexation, and various pericyclic reactions. Therefore, the objective of this study is to review the diverse modes of interaction of TCNE with aromatic nitrogen-containing compounds and to focus the attention of the chemical community on the synthetic capabilities of this reagent, as well as the various biological and optical activities of the structures synthesized based on TCNE.

Design and synthesis of heterocycle-based push-pull NLOphores: A comprehensive study of their linear and non-linear optical properties

Push-pull chromophores, with strong intramolecular charge transfer (ICT), exhibit high ground-state polarization, driving strong NLO responses. The donor and acceptor abilities of the groups in the investigated compounds influence ICT, so the nonlinear response of these compounds was analyzed in relation to their strength. Two different families of NLOphores were synthesized through [2 + 2] cycloaddition-retroelectrocyclizations of heterocycle-based electron-rich alkynes with tetracyanoethylene (TCNE) and tetracyanoquinodimethane (TCNQ). The λmax values of push-pull chromophores, particularly for charge transfer bands, fall within the range of 424–758 nm. The linear and nonlinear optical properties of these NLOphores were subsequently examined through a combination of experimental and theoretical methods. NLO measurements were conducted using a validated custom-made Z-scan device. The nonlinear absorption coefficients range from −1.44 × 10−4 cm.W−1 to −9.90 × 10−4 cm.W−1, while nonlinear refractive indices range from −1.59 × 10−7 cm2. W−1 to −2.26 × 10−6 cm2. W−1. As expected from their molecular structures, the TCNQ products displayed stronger nonlinear responses than the TCNE products.

Charge Density Study of Two-Electron Four-Center Bonding in a Dimer of Tetracyanoethylene Radical Anions as a Benchmark for Two-Electron Multicenter Bonding.

The dimer of the tetracyanoethylene (TCNE) radical anions represents the simplest and the best studied case of two-electron multicenter covalent bonding (2e/mc or pancake bonding). The model compound, N-methylpyridinium salt of TCNE•-, is diamagnetic, meaning that the electrons in two contiguous radicals are paired and occupy a HOMO orbital which spans two TCNE•- radicals. Charge density in this system is studied as a benchmark for comparison of charge densities in other pancake-bonded radical systems. Two electrons from two contiguous radicals indeed form a bonding electron pair, which is distributed between two central ethylene groups in the dimer, i.e., between four carbon atoms. The topology of electron density reveals two bond critical points between the central ethylene groups in the dimer, with maximum electron density of 0.185 e Å-3; the corresponding theoretical value is 0.118 e Å-3.

Electronic behavior of organic molecules adsorbed on monolayer SiC

Studying the adsorption of organic molecules is a good approach for exploring the electronic conducts of two-dimensional (2D) materials. We utilized density functional theory (DFT) to research the structure and electronic behaviors of organic molecules (Tetracyanoquinodimethane(TCNQ), Tetracyanoethylene(TCNE), Tetrathiafulvalene (TTF)) in the SiC adsorption system. After organic molecules are adsorbed on monolayer SiC, the charge difference density (CDD) and the plane average CDD indicate the presence of charge transfer between monolayer SiC and organic molecules. The research results indicate that the impurity energy level appears in the band structure and is contributed by organic molecules. Facts prove that the TCNQ, TCNE, and TTF molecules may inject additional carriers into the SiC layer. TCNQ and TCNE molecules are the electron acceptors, while TTF molecule is the electron donor. The p-type doping and n-type doping were achieved in monolayer SiC, and induce effective p-type doping behavior. Because TCNQ, TCNE, and TTF molecules inject additional holes or electrons into the monolayer SiC, the dimension of the work function can be regulated, expanding the field emission capability range of SiC-based electronic devices. The current-voltage (I-V) curves reveal that after organic molecules adsorbed on monolayer SiC, the transport current capability of the n-type doping system is stronger than the p-type doping system. Therefore, SiC system electrical characteristics may be regulated by organic molecule adsorption. Our work provides a theoretical foundation for SiC application in nano electronic device.

Organic Donor-Acceptor Complexes As Potential Semiconducting Materials.

In this review article, the synthesis, characterization and physico-chemical properties of the organic donor-acceptor complexes are highlighted and a special emphasis has been placed on developing them as semiconducting materials. The electron-rich molecules, i. e., donors have been broadly grouped in three categories, namely polycyclic aromatic hydrocarbons, nitrogen heterocycles and sulphur containing aromatic donors. The reactions of these classes of the donors with the acceptors, namely tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE), tetracyanobenzene (TCNB), benzoquinone, pyromellitic dianhydride and pyromellitic diimides, fullerenes, phenazine, benzothiadiazole, naphthalimide, DMAD, maleic anhydride, viologens and naphthalene diimide are described. The potential applications of the resulting DA complexes for physico-electronic purposes are also included. The theoretical investigation of many of these products with a view to rationalise their observed physico-chemical properties is also discussed.

Anion-π interaction with alkenes: persistent complexes vs. irreversible reactions of anions with tetracyanoethylene.

The interaction of the tetracyanoethylene (TCNE) π-acceptor with oxo- and fluoro-anions (BF4-, PF6-, ClO4-, NO3-) led to the formation of anion-π complexes in which these polyatomic anions were located over the face of alkenes, with multiple contacts being shorter than the van der Waals separations. The anion-π associations of TCNE with halides were delimited by the electron-donor strengths and nucleophilicity of the anions. Specifically, while bromides formed persistent anion-π associations with TCNE in the solid state and in solutions, only transient anion-π complexes with iodides and chlorides were observed. In the case of iodide (strong 1e reducing agent), the formation of anion-π complexes was followed by the reduction of the π-acceptor to the TCNE-˙ anion-radical. The interaction of TCNE with Cl- (and F-) anions (which are better nucleophiles in the aprotic solvents) led to the formation of 1,1,2,3,3-pentacyanoprop-2-en-1-ide anions. Thermodynamics, UV-Vis spectra, and structures, as well as contributions of electrostatics, orbital interactions, and dispersion to the interaction energies in the complexes of TCNE with various anions were closely related to the characteristics of the corresponding associations with the aromatic and p-benzoquinone acceptors. This points out the general equivalence of the interactions in the anion-π complexes with different π-acceptors and the critical role of the nature of the anions in these bindings.

Reaction of tetracyanoethylene with diselenium dichloride: a route to pyrrolo[2,3-c][1,2,6]selenadiazines

Chromatography free, gram scale conversion of tetracyanoethylene (TCNE) into readily functionalised exotic fused pyrrolo[2,3-c][1,2,6]selenadiazines: A new entry into selenium heterocyclic chemistry.

NIR-absorbing TCBD and cyclohexa-2,5-diene-1,4-diylidene-expanded TCBD bridged derivatives of 1,1′-bis(N,N-dimethylaniline)-substituted ferrocene

Symmetrical and unsymmetrical donor-acceptor (D–A) based chromophores were designed and synthesized by the Pd–catalyzed Sonogashira cross–coupling reaction of 1,1′-diiodoferrocene with (4-N,N-dimethylaminophenyl)ethyne followed by [2+2] cycloaddition-retroelectrocyclization reaction with tetracyanoethylene (TCNE) or 7,7,8,8-tetracyanoquinodimethane (TCNQ). Ferrocene was used as a central donor unit and 4-(N,N-dimethylamino)phenyl group as the end-capping donor. Herein, we report the cycloaddition-retrocyclization reaction of TCNE/TCNQ groups on the disubstituted ferrocene containing more than one triple bond to get disubstituted tetracyanobutadiene (TCBD) and cyclohexa-2,5-diene-1,4-diylidene-expanded TCBD products. The effect of the conjugation length and different π–acceptor linkers were investigated by photophysical, redox and computational studies. The redox study reveals multiple oxidation waves corresponding to donor moieties (ferrocene and 4-(N,N-dimethylamino)phenyl group) and reduction waves corresponding to acceptor units (TCBD / cyclohexa-2,5- diene-1,4-diylidene-expanded TCBD). The thermogravimetric analysis data shows that the compounds exhibit high thermal stability. The computational studies reveal HOMO-LUMO gaps consistent with the experimentally obtained data.

Interplay of Adsorption Geometry and Work Function Evolution at the TCNE/Cu(111) Interface.

The adsorption of organic electron acceptors on metal surfaces is a powerful way to change the effective work function of the substrate through the formation of charge-transfer-induced dipoles. The work function of the interfaces is hence controlled by the redistribution of charges upon adsorption of the organic layer, which depends not only on the electron affinity of the organic material but also on the adsorption geometry. As shown in this work, the latter dependence controls the work function also in the case of adsorbate layers exhibiting a mixture of various adsorption geometries. Based on a combined experimental (core-level and infrared spectroscopy) and theoretical (density functional theory) study for tetracyanoethylene (TCNE) on Cu(111), we find that TCNE adsorbs in at least three different orientations, depending on TCNE coverage. At low coverage, flat lying TCNE dominates, as it possesses the highest adsorption energy. At a higher coverage, additionally, two different standing orientations are found. This is accompanied by a large increase in the work function of almost 3 eV at full monolayer coverage. Our results suggest that the large increase in work function is mainly due to the surface dipole of the free CN groups of the standing molecules and less dependent on the charge-transfer dipole of the differently oriented and charged molecules. This, in turn, opens new opportunities to control the work function of interfaces, e.g., by synthetic modification of the adsorbates, which may allow one to alter the adsorption geometries of the molecules as well as their contributions to the interface dipoles and, hence, the work function.

Preparation and Physicochemical Properties of Organic Semiconducting Materials from the Reaction of Imidazo[1,2‐a]pyridines with Tetracyanoethylene

AbstractOrganic donor‐acceptor (DA) complexes have emerged in recent years as materials of choice for organic binary electronics. The reactivity descriptors derived from the conceptual DFT reveal imidazo[1,2‐a]pyridines as potential donors. Thus, four imidazo[1,2‐a]pyridines were reacted with tetracyanoethylene (TCNE) in 1 : 2 molar ratio to afford four new DA complexes. The spectral studies, namely IR, 1H, 13C, DEPT 135, 2D HMQC NMR, and HRMS were used to establish structures of the products. The UV‐vis. spectroscopy reveals intramolecular charge transfer. All the four compounds fluoresce giving excitation emission fluorescence spectra with a red shift ranging from 64 to 151 nm and quantum yields from 0.004 to 16.35. Unexpectedly, nitro group in one of the products does not act as quencher; instead, it enhances the quantum yield to make it highest in this series. The products exhibit electrical conductivity which increases with temperature. The FESEM and HRTEM images reveal distinct and homogenous surface morphology with holes which facilitate flow of electrons as manifested by electrical conductivity. The powder XRD and SAED results establish the polycrystalline nature of the products. The theoretical studies indicate an alternate donor acceptor stacking pattern.

Cycloaddition - Retro-Electrocyclization Click Reaction of Amine End-Capped Oligoynes with Tetracyanoethylene.

Here we show the first example of cycloaddition - retro-electrocyclization (CA-RE) click reaction involving nitrogen end-capped push-pull oligoynes. The reported CA-RE reaction with TCNE (tetracyanoethylene) is fully regioselective and leads exclusively to the unprecedented TCBD (tetracyanobuta-1,3-diene-2,3-diyl) end-capped carbon rods. The molecular structure of products was unambiguously confirmed using X-ray single crystal diffraction and their optical and electronic properties of were investigated experimentally and rationalized using DFT (density functional theory) calculations.

The π‐Molecular Complex of Biphenylene and Tetracyanoethylene

AbstractThe investigation of the biphenylene (BP)‐tetracyanoethylene (TCNE) π‐molecular complex is reported. The first study on this complex appeared in 1961 and was considered as a charge transfer complex with a symmetric, co‐planar arrangement of the components. Moreover, it was assumed that this arrangement is not only dictated by the formation of a Mulliken‐type donor‐acceptor complex, but also by the electronic stabilization of the ‘cyclobutadieneoid’ central ring of biphenylene through complex formation. Yet, crystal structure and associated computational analysis have not verified these predictions so far. We found that factors other than charge‐transfer interactions are most influential in the crystal formation. The low association constant in solution, and the weak interaction between the components in the 1 : 1 crystal structure point towards the low contribution of charge transfer interactions to their binding. Nevertheless, the presence of these interaction is hinted by the color of its solution and verified by theoretical calculations. Furthermore, Nucleus Independent Chemical Shift (NICS) calculations were carried out to characterize potential changes in the (anti)aromatic character of BP upon complex formation. The NICS(0) values of the rings of BP exhibit tiny changes both in the BP‐TCNE dimer and in the crystal, which also suggests weak electronic interactions between them.

A Mechanistic Study about the Formation of Tetracyanobutadienes Revealed an Autocatalytic Behavior

AbstractIn a recent paper in Chemistry – A European Journal, Nielsen and coworkers reported a deep study on the mechanism of the [2+2] cycloaddition‐retroelectrocyclization (CA‐RE) between an electron‐rich alkyne and tetracyanoethylene (TCNE), inducing the formation of a 1,1,4,4‐tetracyanobutadiene (TCBD). Following a robust kinetic study, the authors confirmed important intermediates and determined this reaction to be autocatalytic for the first time. Given the increasing use of TCBDs in the community and the strength of the CA‐RE reaction this paper offers important insights for future developments of this promising reaction.

Clicking together Alkynes and Tetracyanoethylene.

The [2+2] cycloaddition - retro-electrocyclization (CA-RE) reaction allows ready synthesis of redox-active donor-acceptor chromophores from an electron-rich alkyne and electron-poor olefins like tetracyanoethylene (TCNE). The detailed mechanism of the reaction has been subject of both computational and experimental studies. While several studies point towards a stepwise mechanism via a zwitterionic intermediate for the first step, the cycloaddition, the reaction follows neither simple second-order nor first-order kinetics. Recent studies have shown that the kinetics can be understood if an autocatalytic step is introduced in the mechanism, in which complex formation with the donor-substituted tetracyanobutadiene (TCBD) product possibly facilitates nucleophilic attack of the alkyne onto TCNE, generating the zwitterionic intermediate of the CA step. This Concept highlights the convenient use of the "click-like" CA-RE reaction to obtain elaborate donor-acceptor chromophores and the recent mechanistic results.