AFM study of morphological changes associated with electrochemical solid–solid transformation of three-dimensional crystals of TCNQ to metal derivatives (metal = Cu, Co, Ni; TCNQ = tetracyanoquinodimethane)

Cation and anion electrochemically assisted solid-state transformations of malachite green

The possibility of the electrochemical promotion of different solid-to-solid transformations including the performance of successive cation and anion insertion processes has been tested using malachite green, a triphenylmethane dye, in contact with aqueous NaCl electrolyte. Electrochemical data using the voltammetry of microparticles methodology reveal significant differences with the solution phase electrochemistry of the dye. Voltammetric data, combined with atomic force microscopy, focusing ion beam-field emission scanning electron microscopy, and high-resolution field emission scanning electron microscopy permit characterization of the oxidative dissolution, oxidation with anion insertion, reduction with cation insertion and reduction with anion issue processes, whose thermochemical aspects, involving separate ion and electron transport contributions, are discussed.

Correlating growth mechanism and morphology in Cu-TCNQ organometallic complex: A microscopic study

The structure-property correlation in the Cu-TCNQ organometallic complex is very important for explaining its unusual electrical, optical and magnetic properties. Consequently several morphological studies and their correlation with the properties of these materials can be found in the literature, although no systematic study of various morphologies with growth conditions and their correlation has been reported to the best of our knowledge. Therefore in this manuscript the interconversion of various morphologies is reported using electron and probe microscopies. A conventional Cu TEM grid acted as the copper source to form a Cu-TCNQ complex and the complex, which formed at the surface of the TEM grid. The complex thus prepared was characterized by FTIR and Raman spectroscopic techniques. The shifting of ̵-CN from 2221 cm^-1 (TCNQ) to 2201 cm^-1 indicates formation of a complex and the identical nature of IR spectra in two phases indicates that they are polymorphs. The morphologies of Cu-TCNQ were followed through FE-SEM and TEM studies. Various morphologies such as needle, square tube, platelet etc. were observed as a function of time. A distinct transition from needle to platelet morphology was observed as the complex grew. The conductance of various morphologies in phase-I as well as phase-II were also measured and compared by Spreading Resistance Imaging (SRI) at different bias voltage i.e. 1 V, 3 V and 5 V.

An Fe(TCNQ)2 nanowire array on Fe foil: an efficient non-noble-metal catalyst for the oxygen evolution reaction in alkaline media

An Fe-(tetracyanoquinodimethane)₂ nanowire array in situ developed on Fe foil (Fe(TCNQ)₂/Fe) acts as an efficient and durable electrocatalyst for water oxidation, needing an overpotential of 340 mV to attain a current density of 10 mA cm⁻² in 1.0 M KOH.

X4TCNQ2− dianions: versatile building blocks for supramolecular systems

A new synthetic approach has led to the incorporation of TCNQ and F₄TCNQ dianions into a wide variety of structures.

Transportation and Accumulation of Redox Active Species at the Buried Interfaces of Plasticized Membrane Electrodes

The transportation and accumulation of redox active species at the buried interface between glassy carbon electrodes and plasticized polymeric membranes have been studied using synchrotron radiation X-ray photoelectron spectroscopy (SR-XPS), near edge X-ray absorption fine structure (NEXAFS), in situ electrochemical Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy, cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). Ferrocene tagged poly(vinyl chloride) [FcPVC], ferrocene (Fc), and its derivatives together with tetracyanoquinodimethane (TCNQ) doped plasticized polymeric membrane electrodes have been investigated, so as to extend the study of the mechanism of this reaction chemistry to different time scales (both small and large molecules with variable diffusion coefficients) using a range of complementary electrochemical and surface analysis techniques. This study also provides direct spectroscopic evidence for the transportation and electrochemical reactivity of redox active species, regardless of the size of the electrochemically reactive molecule, at the buried interface of the substrate electrode. With all redox dopants, when CA electrolysis was performed, redox active species were undetectable (<1 wt % of signature elements or below the detection limit of SR-XPS and NEXAFS) in the outermost surface layers of the membrane, while a high concentration of redox species was located at the electrode substrate as a consequence of the deposition of the reaction product (Fc(+)-anion complex) at the buried interface between the electrode and the membrane. This reaction chemistry for redox active species within plasticized polymeric membranes may be useful in the fashioning of multilayered polymeric devices (e.g., chemical sensors, organic electronic devices, protective laminates, etc.) based on an electrochemical tunable deposition of redox molecules at the buried substrate electrode beneath the membrane.

A Combined Voltammetric and Synchrotron Radiation-Grazing Incidence X-ray Diffraction Study of the Electrocrystallization of Zinc Tetracyanoquinodimethane

The in situ electrocrystallization of zinc tetracyanoquinodimethane (TCNQ) has been explored using synchrotron radiation-grazing incidence X-ray diffraction (SR-GIXRD) at potentials in the region of the cyclic voltammetric peak where reduction of TCNQ to TCNQ– occurs at a Pt electrode in acetonitrile (0.1 M [NBu4][PF6]) solution containing Zn(NO3)2·6H2O. The in situ SR-GIXRD data along with ex situ IR and Raman spectroscopy results all confirmed the formation of the kinetically favoured phase of Zn[TCNQ]2(H2O)2 as the product.

Novel Semiconducting Biomaterials Derived from a Proline Ester and Tetracyanoquinodimethane Identified by Handpicked Selection of Individual Crystals

Complex mixtures of cation : anion stoichometries often result from the syntheses of tetracyanoquinodimethane (TCNQ) salts, and often these cannot be easily separated. In this study, the reaction of N,N-dimethyl-d-proline-methylester (Pro(CH3)3+) with LiTCNQ resulted in a mixture of crystals. Hand selection and characterisation of each crystal type by X-ray, infrared, Raman and electrochemistry has provided two stoichometries, 1 : 1 [Pro(CH3)3TCNQ] and 2 : 3 ([(Pro(CH3)3)2(TCNQ)3]). A detailed comparison of these structures is provided. The electrochemical method provides an exceptionally sensitive method of distinguishing differences in stoichiometry. The room temperature conductivity of the mixture is 3.1 × 10–2 S cm–1, which lies in the semiconducting range.

Synthesis, Physical Properties, Structural, and Electrochemical Characterization of Methimidazolium and Imidazolium-based Tetracyanoquinodimethane Anion Radical Salts

Two methimazolium and two imidazolium-based salts derived from combination with the tetracyanoquinodimethane (TCNQ) radical anion have been synthesized (1–4). The 1:1 (cation:anion) stoichiometry of the chemically synthesized materials is fully supported by steady-state voltammetric measurements at a microdisc electrode in acetonitrile. The methimazolium TCNQ salts (1 and 2), which contain an acidic proton on the cation, exhibit a protonation step coupled to the TCNQ1–/2– charge-transfer process. Solid–solid transformations at a TCNQ-modified electrode also lead to electrochemical synthesis of 1–4, but also indicate that other cation:anion stoichiometries are accessible. Atomic force microscopy for electrochemically synthesized samples exhibit rod-like morphology. Conductivity measurements on chemically and electrochemically prepared salts are in the semiconducting range. Scanning electrochemical microscopy approach curve data support the substantial conductivity of these solids. Extensive physicochemical characterization of these materials is in complete accordance with the X-ray crystal structure of 1-acetonitrile-3-methylimidazolium tetracyanoquinodimethane, [AMim+][TCNQ1–], 4.

Modified thermodynamics in ionic liquids for controlled electrocrystallization of nanocubes, nanowires, and crystalline thin films of silver-tetracyanoquinodimethane

Electrocrystallization of nanocubes, nanorods, nanowires, and crystalline thin films of silver-tetracyanoquinodimethane (AgTCNQ) onto glassy carbon, indium tin oxide, and platinum electrodes can be achieved from ionic liquids containing dissolved TCNQ and Ag(I) salts. In conventional molecular organic solvents, such as acetonitrile, the reduction of TCNQ and Ag(+) occurs at almost the same potential. In contrast, the different thermodynamics that apply to the room temperature ionic liquid, 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF(4)), give rise to a large potential separation in the two processes, which enables electrocrystallization of AgTCNQ to be undertaken via two distinctly different, potential-dependent mechanisms. Cyclic and microelectrode voltammetric, chronoamperometric, together with microscopic and spectroscopic techniques reveal that AgTCNQ nanostuctures of controlled morphology, size, density, and uniformity can be achieved by tuning the electrocrystallization parameters such as potential, stoichiometric ratio of Ag(+) and TCNQ, and their concentrations, time, and ionic liquid viscosity by altering the water content. In the potential range of -0.1 to 0.3 V vs Fc(0/+) (Fc = ferrocene), electrocrystallization occurs when Ag is deposited at electrode defect sites via a progressive nucleation and 3-D growth mechanism followed by reaction with TCNQ to produce structures ranging from nanocubes to nanowires. At higher stoichiometric concentrations of Ag(+) and more negative potentials (<-0.1 V vs Fc(0/+)), extremely thin crystalline films could be obtained via overpotential deposition. Infrared and Raman spectroscopy, elemental analysis, together with X-ray diffraction and scanning electron microscopy all confirm the formation of highly pure AgTCNQ nanomaterials, which exhibit differences in morphology but not phase. The study highlights the capability of the electrocrystallization method to precisely control the morphology of nanomaterials, and also the unprecedented opportunities provided by using ionic liquids as the medium for preparation of technologically important metal-TCNQ charge transfer complexes.