Coupled protonic and electronic conduction in the molecular conductor [2-(2-1H-Benzimidazolyl)-1H-benzimidazolium]-TCNQ

A novel molecular based proton-electron mixed conductor, (H3BBIM(+))(TCNQ)(Cl(-))(0.5)(H(2)O) (1), where H3BBIM(+) is 2-(2-1H-benzimidazolyl)-1H-benzimidazolium and TCNQ is 7,7,8,8-tetracyano-p-quinodimethane, was synthesized. The salt exhibited peculiar phase transitions as a result of proton-electron coupling phenomena within the crystal. Salt 1 is composed of a closed-shell H3BBIM(+) cation and an open-shell TCNQ anion radical, and was obtained by electrocrystallization in a buffered CH(3)CN solution. Crystal 1 was constructed from the segregated uniform stacks of H3BBIM(+) and TCNQ. The regular stack of partially electron-transferred TCNQ(-0.5) provided a one-dimensional electron-conducting column. Between the regular H3BBIM(+) columns, a channel-like sequence of holes was formed at the side-by-side space that is filled with disordered Cl(-) ions and H(2)O molecules, and which offer a proton-conducting path. The electrical conductivity at room temperature (10 S cm(-1)) was greater by a magnitude of four than the protonic conductivity (1x10(-3) S cm(-1)). Electronic conduction changed from metallic (T>250 K) to semiconducting (250>T>100 K), then insulating (T<100 K). Protonic conductivity was observed above 200 K. The continuous metal-semiconductor transition at 250 K is caused by the formation of the Cl(-) superstructure, whereas the disappearance of protonic conductivity at 200 K is related to the rearrangement of the [Cl(-)-(H(2)O)(2)] sublattice within the channel. The magnetic susceptibility continuously shifted from Pauli paramagnetism (T>250 K) to the one-dimensional linear Heisenberg antiferromagnetic chain (T<250 K). Lattice dimerization in regular TCNQ columns was confirmed by the appearance of vibrational a(g) mode at low temperatures. The strong localization of conduction electrons on each TCNQ dimer caused a Mott transition at 100 K. The melting and freezing of the [Cl(-)-(H(2)O)(2)] sublattice within the channel was correlated to the conduction electrons on the TCNQ stack and the protonic conductivity.     

Conducting Organic Frameworks Based on a Main‐Group Metal and Organocyanide Radicals

Reactions of the main‐group cation Tl^I with anions of 2,5‐derivatives of TCNQ (TCNQ=7,7,8,8‐tetracyanoquinodimethane) have led to the isolation of a family of unprecedented semiconducting main‐group‐metal–organic frameworks, namely, [Tl(TCNQX₂)], (X=H, Cl, Br, I). A comparison of single‐crystal and powder X‐ray diffraction data revealed the existence of a third polymorph of the previously reported material Tl(TCNQ)] and two distinct polymorphs of [Tl(TCNQCl₂)], whereas only one phase was identified for [Tl(TCNQBr₂)] and [Tl(TCNQI₂)]. These new results are described in the context of the structures of other known binary metal–TCNQ frameworks that display a variety of coordination environments for the central cation, namely, four‐, six‐, and eight‐coordinate, and different arrangements of the adjacent TCNQ radicals—parallel versus perpendicular—in the stacked columns. The halogen substituents affect the structures and the properties of these compounds, owing to both steric and electronic effects as evidenced by the semiconducting properties of crystals of [Tl(TCNQCl₂)] phase I, [Tl(TCNQBr₂)], and [Tl(TCNQI₂)], which correlate well with the distances of adjacent TCNQ radicals in the columns. 1D infinite Hückel model simulations of the band structures of [Tl(TCNQCl₂)] phase I, [Tl(TCNQBr₂)], and [Tl(TCNQI₂)] were conducted with and without consideration of the Tl^I cations, the results of which indicate that the charge mobility does not strictly occur in one dimension. The modulations of the band structures with various assumptions of the energy difference (Δ) between the Tl^I 6s orbital and the TCNQ LUMO orbital were calculated and are discussed in light of the observed properties.     

Density Functional Theory Calculations Revealing Metal‐like Band Structures for Ultrathin Germanium (111) and (211) Surface Layers

To find out if germanium possesses facet‐dependent electrical‐conductivity properties, surface‐state density functional theory (DFT) calculations were performed on one to six layers of germanium (100), (110), (111), and (211) planes. Tunable Ge(100) and Ge(110) planes always present the same semiconducting band structure with a band gap of 0.67 eV expected of bulk germanium. In contrast, one, two, four, and five layers of Ge(111) and Ge(211) plane models show metal‐like band structures with continuous density of states (DOS) throughout the entire band. For three and six layers of Ge(111) and Ge(211) plane models, the normal semiconducting band structure was obtained. The plane layers with metal‐like band structures also show Ge−Ge bond‐length deviations and bond distortions, as well as significantly different 4s and 4p frontier‐orbital electron counts and relative percentages integrated over the valence and conduction bands from those of the semiconducting state. These differences should contribute to strikingly dissimilar band structures. The calculation results suggest the observation of facet‐dependent electrical‐conductivity properties of germanium materials; when making transistors from germanium, the facet effects with shrinking dimensions approaching 3 nm may also need to be considered.     

Control of localized nanorod formation and patterns of semiconducting CuTCNQ phase I crystals by scanning electrochemical microscopy

Use of the technique of scanning electrochemical microscopy (SECM) enables the surface of single crystals of 7,7',8,8'-tetracyanoquinodimethane (TCNQ) to be modified in a controlled manner to produce highly dense and micrometer sized regions of semiconducting phase I CuTCNQ nanorod crystals by a nucleation and growth mechanism. This method involves the localized reduction of solid TCNQ to TCNQ- by aqueous phase V(aq)2+ reductant generated at a SECM ultramicroelectrode tip by reduction of V(aq)3+, coupled with the incorporation and reduction of Cu(aq)2+ ions also present in the aqueous electrolyte. SECM parameters can be systematically varied to control the extent of surface modification and the packing density of the CuTCNQ crystals. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images provide evidence that the TCNQ to CuTCNQ solid-solid transformation is accompanied by a drastic localized crystal volume and morphology change achieved by fragmentation of the TCNQ crystal surface. Patterns of semiconducting CuTCNQ (phase I) nanorod shaped crystals have been characterized by SEM, AFM, and infrared (IR) techniques. A reaction scheme has been proposed for the interaction between the electrogenerated mediator V(aq)2+, Cu(aq)2+, and the TCNQ crystal in the nucleation and growth stages of phase I CuTCNQ formation.     

Mesoporous Semimetallic Conductors: Structural and Electronic Properties of Cobalt Phosphide Systems

Mesoporous cobalt phosphide (meso‐CoP) was prepared by the phosphorization of ordered mesoporous cobalt oxide (meso‐Co₃O₄). The electrical conductivity of meso‐CoP is 37 times higher than that of nonporous CoP, and it displays semimetallic behavior with a negligibly small activation energy of 26 meV at temperatures below 296 K. Above this temperature, only materials with mesopores underwent a change in conductivity from semimetallic to semiconducting behavior. These properties were attributed to the coexistence of nanocrystalline Co₂P phases. The poor crystallinity of mesoporous materials has often been considered to be a problem but this example clearly shows its positive aspects. The concept introduced here should thus lead to new routes for the synthesis of materials with high electronic conductivity.     

Conductive Nanoscopic Fibrous Assemblies Containing Helical Tetrathiafulvalene Stacks

Tetrathiafulvalenes (TTF) S‐TTF and R‐TTF having four chiral amide end groups self‐organize into helical nanofibers in the presence of 2,3,5,6‐tetrafluoro‐7,7′,8,8′‐tetracyano‐p‐quinodimethane (F₄TCNQ). The intermolecular hydrogen bonding among chiral amide end groups and the formation of charge‐transfer complexes results in a long one‐dimensional supramolecular stacking, and the chirality of the end groups affects the molecular orientation of TTF cores within the stacks. Electronic conductivity of a single helical nanoscopic fiber made of S‐TTF and F₄TCNQ is determined to be (7.0±3.0)×10^?4 S cm^?1 by point‐contact current‐imaging (PCI) AFM measurement. Nonwoven fabric composed of helical nanofibers shows a semiconducting temperature dependence with an activation energy of 0.18 eV.     

Electrical properties of polyvinylcarbazole-tetracyanoquinodimethane charge transfer complexes

Electrical properties of polyvinylcarbazole-tetracyanoquinodimethane (PVK:TCNQ) charge transfer complexes were investigated as a function of the composition of the mixture, temperature, pressure and the method of sample preparation. It was shown that the electrical conductivity of the PVK:TCNQ complex (for TCNQ content <10% by weight) increased only slowly with increasing concentration of TCNQ and was only slightly higher than the conductivity of pure PVK. At higher TCNQ concentrations however an abrupt increase of the complex conductivity was observed. This effect may be attributed to the formation of semi-conductive tracks composed of uncomplexed neutral TCNQ molecules. The electrical conductivity of PVK:TCNQ complex was lower than the conductivity of TCNQ alone. The activation energy for electrical conductivity in the complex decreased with increasing TCNQ concentration from 0.99 eV for pure PVK to 0.37 eV for PVK:TCNQ (6:1) complex. The high field conductivity of the PVK:TCNQ complex could be explained by using the Poole-Frenkel model.     

Preparation and characterization of [[M(dmb)2]TCNQ.xTCNQo]n polymers (M=Cu,Ag; dmb = 1,8-diisocyano-p-menthane; x = 0, 0.5, 1.0, 1.5; TCNQ = 7,7,8,8-tetracyano-p-quinodimethane) and design of new semi- and photoconducting organometallic materials

New thermoplastic organometallic materials of the type [[M(dmb)2]TCNQ.xTCNQo.y solvent], (M = Cu(I), Ag(I); dmb = 1,8-diisocyano-p-menthane; TCNQ = 7,7,8,8-tetracyano-p-quinodimethane, x = 0, 0.5, 1.0, 1.5; solvent = none, THF or toluene) have been prepared and characterized from X-ray powder diffraction patterns, X-ray crystallography (for some Ag polymers), DSC, and conductivity measurements. While the [[M(dmb)2]TCNQ.xTCNQo]n polymers (M = Cu,Ag; x = 0, 0.5) are insulating, the others (x = 1.0 and 1.5) are semiconducting, and the relative conductivity is found to be a function of the molecular weight and crystallinity. The [[Cu(dmb)2]TCNQ.1.5TCNQ]n material is also photoconducting, while the Ag analogue is not. Photochemical and luminescence quenching experiments in the solid-state established that the Cu+ center and TCNQo act as electron donor and acceptor, respectively, in this photoprocess. Finally photocells of the type glass/SnO2/[Cu(dmb)2]TCNQ.TCNQo]n + 0.5 acceptor/Al (acceptor = TCNQo, C60 and TCNN (13,13,14,14-tetracyano-5,12-naphthacenequinodimethane)) have been designed and characterized. The quantum yields (number of photoproduced electrons/number of photons) are as follows: TCNQ, 1.6 x 10(-4), C60, 5 x 10(-5), TCNN, 3.0 x 10(-4) at lambdaexc = 330 nm. X-ray data for [[Ag(dmb)2]TCNQ.2THF]n: space group P2(1/c), monoclinic, a = 13.5501(10), b = 9.9045(10), c = 32.564(2) A, beta = 91.130(10) degrees, Z = 4. X-ray data for [[Ag(dmb)2]TCNQ.0.5TCNQo.0.5 toluene]n: space group P2(1/c), monoclinic, a = 14.3669(19), b = 9.1659(3), c = 34.012(3) A, beta = 92.140(8) degrees, Z = 4. X-ray data for [[Ag(dmb)2]TCNQ.1.5TCNQo]n: space group C2/c, monoclinic, a = 25.830(11), b = 9.680(2), c = 42.183(19) A, beta = 104.87(4) degrees, Z = 8. X-ray data for [[Ag(dmb)2]DCTC]n: space group P2(1/a), monoclinic, a = 26.273(3), b = 9.730(3), c = 31.526(3) A, beta = 112.12(2)degrees, Z = 4.     

Redox-induced solid-solid phase transformation of TCNQ microcrystals into semiconducting Ni[TCNQ]2(H2O)2 nanowire (flowerlike) architectures: a combined voltammetric, spectroscopic, and microscopic study

The facile solid-solid phase transformation of TCNQ microcrystals into semiconducting and magnetic Ni[TCNQ]2(H2O)2 nanowire (flowerlike) architectures is achieved by reduction of TCNQ-modified electrodes in the presence of Ni2+(aq)-containing electrolytes. Voltammetric probing revealed that the chemically reversible TCNQ/Ni[TCNQ]2(H2O)2 conversion process is essentially independent of electrode material and the identity of nickel counteranion but is significantly dependent on scan rate, Ni2+(aq) electrolyte concentration, and the method of solid TCNQ immobilization (drop casting or mechanical attachment). Data analyzed from cyclic voltammetric and double-potential step chronoamperometric experiments are consistent with formation of the Ni[TCNQ]2(H2O)2 complex via a rate-determining nucleation/growth process that involves incorporation of Ni2+(aq) ions into the reduced TCNQ crystal lattice at the triple phase TCNQ|electrode|electrolyte interface. The reoxidation process, which includes the conversion of solid Ni[TCNQ]2(H2O)2 back to TCNQ0 crystals, is also controlled by nucleation/growth kinetics. The overall redox process associated with this chemically reversible solid-solid transformation, therefore, is described by the equation: TCNQ0(S) + 2e- + Ni2+(aq)+ 2 H2O <==> {Ni[TCNQ]2(H2O)2}(S). SEM monitoring of the changes that accompany the TCNQ/Ni[TCNQ]2(H2O)2 transformation revealed that the morphology and crystal size of electrochemically generated Ni[TCNQ]2(H2O)2 are substantially different from those of parent TCNQ crystals. Importantly, the morphology of Ni[TCNQ]2(H2O)2 can be selectively manipulated to produce either 1-D/2-D nanowires or 3-D flowerlike architectures via careful control over the experimental parameters used to accomplish the solid-solid phase interconversion process.     

Tuning the electrocrystallization parameters of semiconducting Co[TCNQ]2-based materials to yield either single nanowires or crystalline thin films

Electrocrystallization of single nanowires and/or crystalline thin films of the semiconducting and magnetic Co[TCNQ]2(H2O)2 (TCNQ=tetracyanoquinodimethane) charge-transfer complex onto glassy carbon, indium tin oxide, or metallic electrodes occurs when TCNQ is reduced in acetonitrile (0.1 M [NBu4][ClO4]) in the presence of hydrated cobalt(II) salts. The morphology of the deposited solid is potential dependent. Other factors influencing the electrocrystallization process include deposition time, concentration, and identity of the Co2+(MeCN) counteranion. Mechanistic details have been elucidated by use of cyclic voltammetry, chronoamperometry, electrochemical quartz crystal microbalance, and galvanostatic methods together with spectroscopic and microscopic techniques. The results provide direct evidence that electrocrystallization takes place through two distinctly different, potential-dependent mechanisms, with progressive nucleation and 3-D growth being controlled by the generation of [TCNQ]*- at the electrode and the diffusion of Co2+(MeCN) from the bulk solution. Images obtained by scanning electron microscopy reveal that electrocrystallization of Co[TCNQ]2(H2O)2 at potentials in the range of 0.1-0 V vs Ag/AgCl, corresponding to the [TCNQ]0/*- diffusion-controlled regime, gives rise to arrays of well-separated, needle-shaped nanowires via the overall reaction 2[TCNQ]*-(MeCN)+Co2+(MeCN)+2H2O right harpoon over left harpoon {Co[TCNQ]2(H2O)2}(s). In this potential region, nucleation and growth occur at randomly separated defect sites on the electrode surface. In contrast, at more negative potentials, a compact film of densely packed, uniformly oriented, hexagonal-shaped nanorods is formed. This is achieved at a substantially increased number of nucleation sites created by direct reduction of a thin film of what is proposed to be cobalt-stabilized {(Co2+)([TCNQ2]*-)2} dimeric anion. Despite the potential-dependent morphology of the electrocrystallized Co[TCNQ]2(H2O)2 and the markedly different nucleation-growth mechanisms, IR, Raman, elemental, and thermogravimetric analyses, together with X-ray diffraction, all confirmed the formation of a highly pure and crystalline phase of Co[TCNQ]2(H2O)2 on the electrode surface. Thus, differences in the electrodeposited material are confined to morphology and not to phase or composition differences. This study highlights the importance of the electrocrystallization approach in constructing and precisely controlling the morphology and stoichiometry of Co[TCNQ]2-based materials.     

Multiple Active Sites: Lithium Storage Mechanism of Cu‐TCNQ as an Anode Material for Lithium‐Ion Batteries

Recently, carboxylate metal‐organic framework (MOF) materials were reported to perform well as anode materials for lithium‐ion batteries (LIBs); however, the presumed lithium storage mechanism of MOFs is controversial. To gain insight into the mechanism of MOFs as anode materials for LIBs, a self‐supported Cu‐TCNQ (TCNQ: 7,7,8,8‐tetracyanoquinodimethane) film was fabricated via an in situ redox routine, and directly used as electrode for LIBs. The first discharge and charge specific capacities of the self‐supported Cu‐TCNQ electrode are 373.4 and 219.4 mAh g^?1, respectively. After 500 cycles, the reversible specific capacity of Cu‐TCNQ reaches 280.9 mAh g^?1 at a current density of 100 mA g^?1. Mutually validated data reveal that the high capacity is ascribed to the multiple‐electron redox conversion of both metal ions and ligands, as well as the reversible insertion and desertion of Li⁺ ions into the benzene rings of ligands. This work raises the expectation for MOFs as electrode materials of LIBs by utilizing multiple active sites and provides new clues for designing improved electrode materials for LIBs.     

Bottom‐Up On‐Surface Synthesis of Two‐Dimensional Graphene Nanoribbon Networks and Their Thermoelectric Properties

Graphene, the one‐atom‐thick two‐dimensional (2D) carbon material, has attracted tremendous interest in both academia and industry due to its outstanding electrical, mechanical, and thermal properties. For electronic applications, the challenging task is to make it as a semiconductor. The bottom‐up synthesis of semiconducting one‐dimensional (1D) nanometer‐wide graphene strips, namely, graphene nanoribbons (GNRs), has attracted much attention owing to its promising electronic, optical, and magnetic properties. In this regard, we report the fabrication of cove‐type 2D GNR networks (GNNs) via the interconnection of 1D self‐assembled GNRs on the surface of Au(111). The cove‐type 2D GNRs networks (GNNs) were fabricated from the GNR, 5‐CGNR‐1‐1 , synthesized using the precursor of DBSP . Annealing of high‐density self‐assembled GNRs on the surface of Au(111) through two‐zone chemical vapour deposition (2Z CVD) successfully generated a 2D interconnected structure with high yield via the fusion and ladder coupling reactions of GNR chains. In order to validate the later fusion reaction, we have also synthesized the GNR, 7‐AGNR‐1‐1 , using the precursor of DBBA . The GNNs, which consist of hybridized metallic‐like and semiconducting GNRs, are a new class of carbon‐based materials. Further, we applied this material for thermoelectric (TE) applications and found a very low cross‐plane thermal conductivity of 0.11 Wm^?1 K^?1, which is one of the lowest value among the carbon‐based materials as well as inorganic semiconductors, while maintaining the cross‐plane electrical conductivity of 188 S m^?1.     

Donor–acceptor complex of a new bis‐TTF donor containing a pyridine diester spacer with TCNQ as the acceptor: a disappointing system

A new bis‐TTF donor (TTF is tetrathiafulvalene) containing a pyridine diester spacer, namely bis{2‐[(6,7‐tetramethylene‐3‐methylsulfanyltetrathiafulvalen‐2‐yl)sulfanyl]ethyl} pyridine‐2,6‐dicarboxylate–tetracyanoquinodimethane–dichloromethane (2/1/2), 2C₃₃H₃₃NO₄S₁₂·C₁₂H₄N₄·2CH₂Cl₂, has been synthesized and its electron‐donating ability determined by cyclic voltammetry. The electrical conductivity and crystal structure of this donor–acceptor (DA) complex with TCNQ (tetracyanoquinodimethane) as the acceptor are presented. The TCNQ moiety lies across a crystallographic inversion centre. In the crystal structure, TTF and TCNQ entities are arranged in alternate stacks; this feature, together with the bond lengths of the TCNQ molecule, suggest that the expected charge transfer has not occurred and that the D and A entities are in the neutral state, in agreement with the poor conductivity of the material (σ_RT = 2 × 10⁻⁶ S cm⁻¹).     

Adapting semiconducting polymer doping techniques to create new types of click postfunctionalization

After the historical development from the insoluble polyacetylene film to soluble and processible aromatic polymers, donor-acceptor-type aromatic polymers have recently emerged as a new class of semiconducting polymers. The polymer energy levels and band gaps can be tuned by the appropriate selection of the donor and acceptor moieties, and some of these polymers showed good optoelectronic or photovoltaic performances. The conventional synthetic method for achieving donor-acceptor-type aromatic polymers is based on the metal-catalyzed polycondensation between donor-type monomers and acceptor-type co-monomers. In this tutorial review, a new methodology for introducing donor-acceptor chromophores into semiconducting polymers is described. The donor-acceptor structures are constructed in the main chains and side chains of semiconducting polymers using a polymer reaction based on high-yielding addition reactions between the electron-rich alkynes and strong acceptor molecules, such as tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ). Considering the p-type doping features of TCNE and TCNQ, the experimental procedure is the same as the conventional doping technique for semiconducting polymers. However, the resulting donor-acceptor type polymers are chemically stable due to the absence of unstable unpaired electrons (polarons). The donor-acceptor alternating polymers were achieved in one step from the precursor poly(aryleneethynylene)s and poly(arylenebutadiynylene)s. When the side chain alkynes were post-functionalized, the polymer energy levels were controlled by the species and amount of the employed acceptor molecules. These atom-economic acceptor additions satisfy most of the requirements of the "click chemistry" concept. In contrast to the conventional click chemistry reactions, the reactions between electron-rich alkynes and acceptor molecules provide a wide variety of polymers with promising optoelectronic applications.     

Preferential Face‐on and Edge‐on Orientation of Thiophene Oligomers by Rational Molecular Design

Precise control over the supramolecular organization of organic semiconducting materials guiding to exclusive face‐on or edge‐on orientation is a challenging task. In the present work, we study the preferential packing of thiophene oligomers induced through rational molecular designing and self‐assembly. The acceptor–donor–acceptor‐type oligomers having 2‐(1,1‐dicyano‐methylene)rhodanine as acceptor ( OT1 ) favored a face‐on packing, whereas that of functionalized with N‐octyl rhodanine ( OT2 ) preferred an edge‐on packing as evident from 2D‐grazing incidence angle X‐ray diffraction, tapping‐mode atomic force microscopy (AFM) and Raman spectroscopy analyses. The oligomers exhibited anisotropic conductivity in the self‐assembled state as an outcome of the preferred orientation, revealed by the conducting AFM experiment.     

The Role of Weak Interactions in the Mechano‐induced Single‐Crystal‐to‐Single‐Crystal Phase Transition of 8‐Hydroxyquinoline‐Based Co‐crystals

Mechano‐induced single‐crystal‐to‐single‐crystal (SCSC) phase transitions in crystalline materials that change their properties have received more and more attention. However, there are still too few examples to study molecular‐level mechanisms in the mechano‐induced SCSC phase transitions, making the systematic and in‐depth understanding very difficult. We report that bis‐(8‐hydroxyquinolinato) palladium(II)‐tetracyanoquinodimethane (PdQ₂‐TCNQ) and bis‐(8‐hydroxyquinolinato) copper(II)‐tetracyanoquinodimethane (CuQ₂‐TCNQ) show very different mechano‐response behaviors during the SCSC phase transition. Phase transition in CuQ₂‐TCNQ can be triggered by pricking on the crystal surface, while in PdQ₂‐TCNQ it can only be induced by applying pressure uniformly over the whole crystal face. The crystallography data and Hirshfeld surface analysis indicate that the weak intra‐layer C?H???O, C?H???N hydrogen bonds and inter‐layer stacking interactions determine the feasibility of the SCSC phase transition by mechanical stimuli. Weaker intra‐layer interactions and looser inter‐layer stacking make the SCSC phase transition occur much more easily in the CuQ₂‐TCNQ.     

Energy level tuning of polythiophene derivative by click chemistry‐type postfunctionalization of side‐chain alkynes

A polythiophene derivative substituted with electron‐rich alkynes as a side chain was synthesized using the Suzuki polycondensation reaction. The electron‐rich alkynes underwent the “click chemistry”‐type quantitative addition reaction with strong acceptor molecules, such as tetracyanoethylene (TCNE) and 7,7,8,8‐tetracyanoquinodimethane (TCNQ), resulting in the formation of donor–acceptor chromophores. All polymers showed excellent solubilities in the common organic solvents as well as good thermal stabilities with their 5% decomposition temperatures exceeding 230 °C. The TCNE‐/TCNQ‐adducted polymers displayed well‐defined charge‐transfer (CT) bands in the low energy region. The CT energy of the TCNE‐adducted polymer was 2.56 eV (484 nm), which was much greater than that of the TCNQ‐adducted polymer [1.65 eV (750 nm)]. This result was supported by the electrochemical measurements. The electrochemical band gaps of the TCNE‐adducted polymers were much greater than those of the corresponding TCNQ‐adducted polymers. Furthermore, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels, determined from the first oxidation and first reduction peak potentials, respectively, decreased with the increasing acceptor addition amount. All these results suggested that the energy levels of the polythiophene derivative can be tuned by varying the species and amount of the acceptor molecules using this postfunctionalization method. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Infrared and Raman spectroscopic evidence of ground state charge densities at TCNQ sites in crystalline Cs2 (TCNQ)3

The reported Raman spectrum of the Rb TCNQ salt allows, for the first time, examination of all the vibrational features of the TCNQ ^? radical anion. The knowledge of the TCNQ fundamental frequencies as well as of those for neutral TCNQ makes it possible to interpret the infrared and Raman spectra of Cs₂ (TCNQ)₃ and to conclude that in this salt both neutral and negatively charged TCNQ units are present in the crystal. The result is a first fruitful application of vibrational spectroscopy to the study of complex TCNQ salts, opening the way to an extensive investigation of TCNQ semiconducting salts.     

Application of F4TCNQ doped spiro-MeOTAD in high performance solid state dye sensitized solar cells

Amid the investigation of solid-state dye-sensitized solar cells (SDSSCs), it was found that the incorporation of F4TCNQ into the solid hole-transporting materials (HTMs) spiro-MeOTAD forms a spiro-MeOTAD/F4TCNQ (strong electron acceptor) polaron charge-transfer complex. Careful examination indicates that the formation of the polaron charge-transfer complex not only facilitates the conductivity of HTMs but also inhibits the charge recombination across the interface of the heterojunction, i.e. photoanode/HTMs and/or counter electrode/HTMs. As a result, the performance of SDSSCs has been markedly improved by using the organic dye A2-F. At AM1.5 illumination the short circuit current densities J(SC) increase from 8.29 mA cm(-2) (w/o F4TCNQ) to 10.95 mA (w/F4TCNQ), accompanied by a 20% increase of the overall power conversion efficiency, η, from 4.55% to 5.44%.     

Mediated Electron Transfer Across Supported Bilayer Lipid Membrane with TCNQ‐Based Organometallic Compounds

Supported bilayer lipid membrane (s‐BLM) containing one‐dimensional compound 1, TCNQ‐based (TCNQ=7,7,8,8‐tetracyanoquinodimethane) organometallic compound {(Cu₂(μ‐Cl)(μ‐dppm)₂)(μ₂‐TCNQ)}_∞, was prepared and characterized on the self‐assembled monolayer (SAM) of 1‐octadecylmercaptan (C₁₈H₃₇SH) deposited onto Au electrode. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) results showed that the compound 1, dotted inside s‐BLM, can act as mediator for electron transfer across the membrane. Two redox peaks and the charge‐transfer resistance of 400 kΩ were observed for compound 1 inside s‐BLM. The mechanism of the electron transfer across s‐BLM by TCNQ is by electron hopping while TCNQ‐based organometallic compound is by conducting. Further conclusion drawn from this finding is that the TCNQ‐based organometallic compound embedded inside s‐BLM exhibits excellent electron transfer ability than that of free TCNQ. This opens a new path for the development of s‐BLM sensor and/or biosensor by incorporation with TCNQ‐based organometallic compounds.