Tetracyanoethylene Research Articles

A coordinatively saturated cobalt complex as a new kind catalyst for efficient electro- and photo-catalytic hydrogen production in purely aqueous media

It has been shown that coordinatively unsaturated complexes can catalyze hydrogen production via an unstable hydride intermediate. Herein we present a new kind of water soluble catalyst based on a coordinatively saturated cobalt complex, [(phen)2Co(CN)2]⋅ClO41 that is formed by the reaction of 1,10-phenanthroline (phen), Co(ClO4)2·6H2O and tetracyanoethylene (TCNE). Under photoirradiation with blue light (λmax = 469 nm) in air, together with [Ru(bpy)3]Cl2 and ascorbic acid in a pH 5.5 aqueous solution, 1 possesses photocatalytic activity for water reduction to hydrogen with an initial turnover number (TON) of 1232H2 per mol of catalyst at first 10 h, and this activity is sustained for at least 70 h. This can be attributed to that oxidative quenching by 1 (kq = 1.69 × 1010 M−1 s−1) dominates over reductive quenching to [Ru(bpy)3]Cl2 by ascorbic acid (kq = 1.55 × 1010 M−1 s−1). Additionally, 1 electrocatalyze hydrogen generation from a neutral water with a turnover frequency (TOF) of 1113.1 mol of hydrogen per mole of catalyst per hour (mol H2/mol catalysts/h) at an overpotential (OP) of 838 mV. We hope this can afford a new method in proton or water reduction catalysis using coordinatively saturated complexes in purely aqueous media.

Photoinduced charge-transfer electronic excitation of tetracyanoethylene/tetramethylethylene complex in dichloromethane

Based on the previous work on nonequilibrium solvation model by the authors, Intermolecular charge-transfer electronic excitation of tetracyanoethylene (TCE)/tetramethylethylene (TME) π-stacked complex in dichloromethane (DCM) has been investigated. For weak interaction correction, dispersion corrected functional DFT-D3 is adopted for geometry optimization. In order to identify the excitation metric, dipole moment components of each Cartesian direction, atomic charge, charge separation and Δr index are analyzed for TCE/TME complex. Calculation shows that the calculated excitation energy is dependent on the functional choice, when conjuncted with suitable time-dependent density functional, the modified nonequilibrium expression gives satisfied results for intermolecular charge-transfer electronic excitation.

Colorimetric Ion Sensors Based on Polystyrenes Bearing Side Chain Triazole and Donor-Acceptor Chromophores.

Side chain clicked polystyrene derivatives formed by the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction showed colorimetric ion sensing behaviors when donor-acceptor chromophores, prepared by a [2+2] cylcoladdition-retroelectrocyclization between electron-rich alkynes and tetracyanoethylene (TCNE)/7,7,8,8-tetracyanoquinodimethane (TCNQ), were attached to the triazole rings. The metal ion sensing behaviors could be explained according to the theory of hard and soft acids and bases (HSAB). Hard acidic metal ions were mainly recognized by the hard basic anilino-nitrogen moieties, resulting in a decrease in the charge-transfer (CT) bands. In contrast, soft acidic metal ions led to a bathochromic shift in the CT bands due to the selective interactions with the soft basic cyano-nitrogen atoms. With the triazole spacers, more soft (and/or borderline) metal ions were recognized by the donor-acceptor chromophores probably due to more space for the various sized metal ions. The chemodocimetric anion sensing behaviors of the clicked polystyrenes were almost the same as those of the counter polystyrenes without the triazole spacers. Overall, the triazoles in this study do not serve as colorimetric sensor units towards both metal ions and anions, but they are effective spacers between the polymer main chain and ion sensing donor-acceptor side chain chromophores.

Synthesis, physical properties, and chemistry of donor–acceptor-substituted pentacenes

Pentacenes bearing electron-donating and (or) -withdrawing groups, namely methoxy-, dialkylamino-, and nitroaryl moieties, are synthesized to afford polarized pentacenes. The optical, electrochemical, and chemical properties of these derivatives are explored. The cycloaddition reaction of selected derivatives with tetracyanoethylene (TCNE) is explored, and the experimental results are rationalized on the basis calculations using density functional theory (DFT). X-ray crystallographic data provides insight into the molecular structure and intermolecular interactions present in the solid state.

An N‐Heterocyclic‐Carbene–Tetracyanoethylene Zwitterion: Experimental and Theoretical Study on Its Formation and Reactivity

The direct addition of tetracyanoethylene (TCNE) to the carbene center of 1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene (IPr) was successfully demonstrated. The IPr–TCNE adduct, that is, zwitterion 1, clearly differs from the typical [2+1]‐cycloaddition products obtained from the reaction of carbenes with olefins. The results obtained from experimental and theoretical studies suggest that adduct 1 disassembles into IPr and TCNE, which is followed by the addition of IPr to the nitrile carbon atom of TCNE and subsequent isomerization into a thermodynamically more stable singlet nitrene intermediate. This intermediate is then captured by an additional molecule of TCNE to afford another heterocycle. This study reveals a unique example of the reactivity between N‐heterocyclic carbenes and olefins.

The nature of the multicenter bonding in π-[TCNE]22− dimer: 4c/2e, 12c/2e, or 20c/2e?

Composition of the 20c–2e bonding orbital in the π-[TCNE]22− dimer, and the partial occupancy numbers C1, C2 and N in the 20c–2e bond.

Photoluminescence quenching of inorganic cesium lead halides perovskite quantum dots (CsPbX3) by electron/hole acceptor.

Recently, all-inorganic cesium lead halide perovskites (CsPbX3) quantum dots (QDs) have attracted great attention due to their halogen composition and size tunable band gap engineering, the same physical mechanism that is responsible for excellent performance in light-emitting devices. However, little is known about the time-resolved fluorescence quenching dynamics process of these CsPbX3 QDs. In this article, we present comprehensive contrastive spectral studies on the electron and hole extraction dynamics of CsPbX3 colloidal QDs with and without quencher by time-resolved femtosecond transient absorption (TA) and time-correlated single-photon counting (TCSPC) spectroscopy methods. We have identified that the partial electrons of the conduction band and holes of the valence band of CsPbX3 QDs can be directly extracted by tetracyanoethylene (TCNE) and phenothiazine (PTZ), respectively. Moreover, compared with the CsPbBr3 QDs, the CsPbI3 QDs showed relatively slower charge extraction rates. We also found that the CsPbBr3 QDs with smaller size showed faster carrier recombination rates and photoluminescence (PL) decay lifetime due to the relatively stronger quantum confinement effects. We believe that this study may be useful for realising optimal applications in photovoltaic and light emission devices.

Nanocarbons as Electron Donors and Acceptors in Photoinduced Electron-Transfer Reactions

Nanocarbons composed of hybridized sp2 carbons such as fullerenes, carbon nanotubes (CNTs), carbon nanohorns (CNHs) and graphene have been successfully utilized as electron acceptors in electron donor-acceptor hybrids for photoinduced electron-transfer reactions to mimic well the function of the photosynthetic reaction center. However, sp2 hybridized nanocarbons can also be used as electron donors when higher fullerenes such as C76 and C78 or endohedral metallofullerenes are employed or when nanocarbons are combined with relatively strong electron acceptors. This paper focuses on photoinduced electron-transfer reactions of nanocarbons including fullerenes, CNTs, CNHs and graphene, which act as not only as electron acceptors but also as electron donors with strong electron acceptors such as tetracyanoethylene (TCNE) and tetracyano-p-quinodimethan (TCNQ) to produce the radical cations efficiently because of small reorganization energies of electron transfer. Alternatively the oxidizing ability of electron acceptors was enhanced by binding Lewis acids to the radical anions, which enabled to oxidize nanocarbons. The important roles of nanocarbons such as fullerenes, carbon nanotubes and graphenes on the stability of rapidly emerging perovskite based solar cells with high power conversion efficiency have also been discussed in this paper.

Hollow and microporous triphenylamine networks post-modified with TCNE for enhanced organocathode performance.

Hollow microporous triphenylamine networks (H-MTPN) were post-modified with tetracyanoethylene (TCNE) to generate tetracyanobutadiene moieties in H-MTPN-TCNE. The H-MTPN-TCNE showed the improved electrochemical performance of cathode materials for lithium ion batteries, compared to the original H-MTPN.

Change in optoelectronic properties of ExBox+4 on functionalization and guest encapsulation.

The impact of functionalization as well as guest encapsulation on the optoelectronic properties of the ExBox+4 moiety has been investigated with the aid of density functional theory (DFT) based calculations. To this end, three functionalized variants of the ExBox+4 moiety have been modelled in silico, viz. NH2-ExBox+4-F, CN-ExBox+4-NH2 and NO2-ExBox+4-NH2, whereas coronene (Cor), B-doped coronene (BCor), N-doped coronene (NCor), tetrathiafulvalene (TTF), biphenyl (BiPh), tetracyanoethylene (TCNE) and tetracyanoquinodimethane (TCNQ) molecules have been employed as guests. The results indicate that as a result of functionalization, the ExBox+4 moiety can exhibit tangible non-linear optical (NLO) response properties as vindicated by the first static hyperpolarizability (β). As a result of guest encapsulation, significant variation in the optoelectronic properties of the chosen hosts takes place. BCor/TCNQ/NCor molecules enhance the NLO activity of the hosts while TTF/TCNE suppresses the same. In particular, NCor@host moieties demonstrate very high β values at the static field limit. Time dependent DFT results suggest that in general, the ability of the guest in tuning the transition energy associated with the pivotal electronic transitions of the host plays the dominant role in the observed variation in β. In addition, BCor/NCor@host moieties demonstrate broadband optical absorption capability thereby elucidating the possibility of deriving multi-purpose optoelectronic features such as NLO activity as well as utility in photovoltaic systems. Thermochemical results suggest that all the guest@host systems are stable at 298.15 K. Non-covalent and electrostatic binding forces stabilize the studied systems.

Reactivity of tetracyanoethylene (TCNE): Synthesis and catalytic properties of a nickel complex supported by pentacyanopropenide derived from TCNE

The reaction of 2,2-bipyridine (bpy), NiCl2·6H2O and tetracyanoethylene (TCNE) affords a nickel complex, [Ni(bpy)3]⋅(PCPP)21 (PCPP: pentacyanopropenide, a compound derived from TCNE). Its structure has been characterized by physics-chemical and spectroscopic methods. This complex can electrocatalyze hydrogen generation both from acetic acid, with a turnover frequency (TOF) of 152.88mol of H2 per mole of catalyst per hour an overpotential (OP) of 941.6mV (in CH3CN), and from aqueous buffer (pH7.0) with a TOF of 1464mol of H2 per mole of catalyst per hour at an OP of 837.6mV.

Soft versus hard junction formation for α-terthiophene molecular wires and their charge transfer complexes

We used a range of scanning tunnelling microscopy (STM)-based methods to conduct a detailed study of single molecule junction conductance enhancement upon charge transfer complex formation, using bis(thiaalkyl)arene molecular wires as electron donors and tetracyanoethylene (TCNE) as an electron acceptor. Using the “hard” STM break junction (STM-BJ) method, in which a Au STM tip is pushed into a Au substrate and then withdrawn in the presence of molecules, we see a single, very broad, peak in the resulting conductance histogram when all data are used; the conductance enhancement is 25-fold for a terthiophene donor and 15-fold for a phenyl group. After rational data selection, in which only current-distance curves that contain a current plateau >0.2 nm long are used in the conductance histogram, three sharper peaks are resolved in the histograms for the charge transfer complexes; two substantially lower-conductance peaks are resolved for the uncomplexed molecules. Using the “soft” STM I(s) technique, in which initial contact between tip and substrate is avoided and the current limit is about an order of magnitude lower, we were able to resolve two peaks for the uncomplexed molecules depending upon the initial set point current (i.e., tip height), one at the same value as the lower of the two data-selected STM-BJ histogram peaks and an additional peak beyond the low-current limit for the STM-BJ experiment. For the terthiophene, the low, medium, and high conductance peaks for the TCNE complex are, respectively, ca. 70, 70, and 46 times higher in conductance than the corresponding peaks for the free molecule.

Modulating Carrier Density and Transport Properties of MoS2 by Organic Molecular Doping and Defect Engineering

Using first-principles calculations, we investigate the effect of molecular doping and sulfur vacancy on the electronic properties and charge modulation of monolayer MoS2. It is found that tetrathiafulvalene and dimethyl-p-phenylenediamine molecules are effective donors, whereas tetracyanoethylene (TCNE) and tetracyanoquinodimethane (TCNQ) are effective acceptors, and all these molecules are able to shift the work function of MoS2. For MoS2 containing sulfur vacancies, these molecules are able to change the position of the defect levels within the band gap and modulate the carrier density around the defect center. Charge transfer analysis shows that TCNE and TCNQ induce a free-carrier depletion of the defect states, which is beneficial for the suppression of the nonradiative trionic decay and a higher excitonic efficiency due to a decrease in the screening of excitons. Furthermore, the effects of molecular adsorption on Seebeck coefficient of MoS2 are also explored. Our work suggests that an enhanced exci...

Spectrophotometric and thermodynamic studies on the 1:1 charge transfer interaction of several clinically important drugs with tetracyanoethylene in solution-state: Part one

The occurrence and environmental fate of pharmaceuticals represents a rising and significant public concern worldwide. To provide basic data that can be used to detect and determine several drugs in such environments, this work examines the charge transfer (CT) interaction of tetracyanoethylene (TCNE) as a π-acceptor with eight drugs by spectrophtometry in acetonitrile (MeCN). All of the drugs formed stable yellow compounds with TCNE. The results show that the complexation stoichiometry of TCNE/drug is 1:1. Several spectroscopic and thermodynamic parameters were estimated using the Benesi–Hildebrand and Van't Hoff's equations. Very strong linear correlations were observed between the thermodynamic parameter. The IR data suggest that the complexation between TCNE and drugs occurs via n→π* and/or π→π* interactions.

Synthesis, characterization and properties of a copper complex with dicyano acetic acid methyl ester ligand derived from tetracyanoethylene

The reaction of CuCl with tetracyanoethylene (TCNE) affords a copper(II) complex, [(DCAE)2Cu(H2O)2] 1 (DCAE: dicyano-acetic acid methyl ester, derived from TCNE). Its structure has been characterized by physics-chemical and spectroscopic methods. Magnetic studies exhibit that no magnetic coupling between two Cu2+ via DCAE− unit in the temperature range 300–9K. Electrochemical studies show that this copper complex can act as an electrocatalyst for hydrogen generation both from acetic acid, with a turnover frequency (TOF) of 74mol of H2 per mole of catalyst per hour an potential (OP) of 941.6 (in CH3CN), and from aqueous buffer (pH 7.0) with a TOF of 285mol of H2 per mole of catalyst per hour at an OP of 787.6mV.

A water soluble electro-catalyst for generating hydrogen based on a cobalt(III) complex supported by 1,10-phenanthroline

As we know, coordinatively unsaturated complexes can catalyze hydrogen generation via an unstable hydride intermediate. In this paper, we report an electrocatalyst based on a water soluble coordinatively saturated complex, [(phen)2Co(CN)2]·NO31 that is formed by the reaction of 1,10-phenanthroline (phen), Co(NO3)2·6H2O and tetracyanoethylene (TCNE). Its structure has been characterized by physics-chemical and spectroscopic methods. Complex 1 can electrocatalyze hydrogen evolution both from acetic acid and aqueous buffer.

Spectrophotometric and spectroscopic studies on charge transfer complexes of the antifungal drug clotrimazole

Clotrimazole (CLZ) is an imidazole derivative that is therapeutically used as an antifungal drug. The routine control analysis of CLZ requires rapid, reliable, accurate and precise methods for the quantification of the drug in its pharmaceutical formulations. Spectrophotometric methods are presented for the determination of the antifungal agent that are based on the charge transfer complexation reaction of CLZ with the π-acceptors tetracyanoethylene (TCE) and 7,7′,8,8′-tetracyanoquinodimethane (TCNQ). The formation of coloured complexes was quantitated at 396nm and 842nm for CLZ-TCE and CLZ-TCNQ, respectively, which enabled the development of simple and accurate spectrophotometric methods for the analysis of CLZ in pure drug substances and its pharmaceutical products. Under the optimum reaction conditions, linear relationships with appreciable correlation coefficients (0.9985–0.9994) were found between the absorbance at the relevant maxima and the concentrations of CLZ in the range of 5.00–35.00μgmL−1 for CLZ-TCE and 1.00–25.00μgmL−1 for CLZ-TCNQ. The molar absorptivities and Sandell's sensitivity values were also statistically evaluated. The proposed methods were successfully applied to analyze CLZ in topical creams and sterile solutions with mean recovery percentages in the range of 99.60–100.20%, which indicated no interference from the inactive ingredients. Furthermore, the charge transfer complexes of CLZ were also characterized by FT-IR spectroscopy.

Pathway-Dependent Post-assembly Modification of an Anthracene-Edged M(II)4L6 Tetrahedron.

Fe(II)4L6 tetrahedral cage 1 undergoes post-assembly modification (PAM) via a Diels-Alder cycloaddition of the anthracene panels of the cage with tetracyanoethylene (TCNE). The modified cage 2 possesses an enclosed cavity suitable for encapsulation of the fullerene C60, whereas original cage 1 forms a unique covalent adduct through a Diels-Alder cycloaddition of three of its anthracene ligands with C60. This adduct undergoes further PAM via reaction of the remaining three ligands with TCNE, enabling the isolation of two distinct products depending on the order of addition of C60 and TCNE. Modified cage 2 was also able to bind an anionic guest, [Co(C2B9H11)2](-), which was not encapsulated by the original cage, demonstrating the potential of PAM for tuning the binding properties of supramolecular hosts.

Energy-level tuning of poly(p-phenylenebutadiynylene) derivatives by click chemistry-type postfunctionalization of side-chain alkynes

A series of poly(p-phenylenebutadiynylene) polymers substituted with electron-rich alkynes as the side chain were synthesized by homocoupling polymerization of asymmetric bifunctional monomers. The electron-rich alkynes underwent “click chemistry” with tetracyanoethylene (TCNE) to produce donor–acceptor chromophores. Optical and electrochemical characterizations clearly indicated that the energy level and band gap of P2 could be precisely controlled by the addition of acceptor molecules. One of the most important conclusions of this study is that a linear relationship between the lowest occupied molecular orbital (LOMO) and the amount of TCNE was observed. From the Z-scan measurement, all the compounds exhibited very special nonlinear optical properties, which suggested a tendency to transfer from saturable absorption (SA) to reverse saturable absorption (RSA).

Charge transfer complexes between 2-, 3- and 4-aminopyridines and some π-acceptors in the gas phase and in chloroform: DFT calculations

This work reports density functional theory (DFT) calculations on the molecular structures, electronic distribution, and UV-Vis and IR spectroscopy analysis of charge transfer complexes between aminopyridines (APYs), namely 2-APY, 3-APY and 4-APY, as electron-donors and some [Formula: see text]-electron-acceptors, namely chloranil (CHL), tetracyanoethylene (TCNE) and picryl chloride (PC), formed in the gas phase at the B3LYP/6-31[Formula: see text]G(d,p) method/basis set, and in chloroform at the same method/basis set using PCM as solvation model. Good correspondence was generally obtained between the calculated parameters and the experimental ones.