Solid-state Charge-transfer Complexes Research Articles

(Invited) Ion Transport in Solid-State Electrolytes Based on TTF - TCNQ Charge-Transfer Complexes

Current research on solid-state organic electrolytes mainly focuses on polymer electrolytes where ion transport is facilitated by chain segmental motion. The ionic conductivity of these polymer electrolytes at room temperature in too low for many practical applications. A limited number of prior reports suggest that solid-state electrolytes including organic crystalline charge-transfer complexes can have surprisingly high ionic conductivity. We report1 that processing and environmental conditions drastically impact electron and ion charge transport properties of charge-transfer complex electrolytes based on tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) mixed with lithium bis(trifluoromethylsulfonylimide) (LiTFSI). Thermal annealing and water vapor treatment decrease electronic conductivity and increase ionic conductivity. The electrolyte with 1-1-2-0.45 molar ratio of TTF-TCNQ-LiTFSI-H2O has an ionic conductivity of 2 × 10-3 S/cm at 25 °C with electronic conductivity of order 10-7 S/cm. Thermal annealing helps reduce connectivity of the charge-transfer complexes and expose more surfaces to interact with LiTFSI, thereby decreasing electronic conductivity. Exposure of the sample to water vapor then causes a substantial increase in ionic conductivity, even when the material remains in the solid state. In this presentation, we will also report on additional experimental studies of solid-state electrolytes incorporating TTF-TCNQ.Reference 1. L. Yang and J. L. Schaefer, “Water-Assisted Ion Conduction in Solid-State Charge-Transfer Complex Electrolytes for Lithium Batteries,” ChemRxiv, 2023. https://doi.org/10.26434/chemrxiv-2023-9k024

Grinding-induced supramolecular charge-transfer assemblies with switchable vapochromism toward haloalkane isomers

Synthetic macrocycles have proved to be of great application value in functional charge-transfer systems in the solid state in recent years. Here we show a switchable on-off type vapochromic system toward 1-/2-bromoalkane isomers by constructing solid-state charge-transfer complexes between electron-rich perethylated pillar[5]arene and electron-deficient aromatic acceptors including 4-nitrobenzonitrile and 1,4-dinitrobenzene. These charge-transfer complexes with different colors show opposite color changes upon exposure to the vapors of 1-bromoalkanes (fading) and 2-bromoalkanes (deepening). Single-crystal structures incorporating X-ray powder diffraction and spectral analyses demonstrate that this on-off type vapochromic behavior is mainly attributed to the destruction (off) and reconstruction (on) of the charge-transfer interactions between perethylated pillar[5]arene and the acceptors, for which the competitive host-guest binding of 1-bromoalkanes and the solid-state structural transformation triggered by 2-bromoalkanes are respectively responsible. This work provides a simple colorimetric method for distinguishing positional isomers with similar physical and chemical properties.

Water-Assisted Ion Conduction in Solid-State Charge-Transfer Complex Electrolytes for Lithium Batteries

Current research on solid-state organic electrolytes mainly focuses on polymer electrolytes where ion transport is facilitated by chain segmental motion. A limited number of prior reports suggest that solid-state electrolytes based on organic charge-transfer (CT) complexes can have surprisingly high ionic conductivity. Here, we report that processing and environmental conditions drastically impact charge transport properties of CT complex electrolytes based on tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) mixed with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Thermal annealing and water vapor treatment decreases electronic conductivity and increases ionic conductivity. The electrolyte with a 1-1-2-0.45 molar ratio of TTF-TCNQ-LiTFSI-H2O has an ionic conductivity of 2 × 10–3 S/cm at 25 °C with order 104 times lower electronic conductivity. In this system where ion conduction is decoupled from the mobility of the organic phase, thermal annealing helps reduce CT connectivity and expose more surfaces to interact with LiTFSI, and water promotes the dissociation of LiTFSI.

Synthesis, spectroscopic and computational characterization of charge transfer complex of remdesivir with chloranilic acid: Application to development of novel 96-microwell spectrophotometric assay

Remdesivir (REM) is an adenosine triphosphate analog antiviral drug that has received authorization from European Commission and approval from the U.S. Food and Drug Administration for treatment of coronavirus disease 2019 (Covid-19). This study, describes, for the first time, the synthesis of a novel charge transfer complex (CTC) between REM, as electron donor, with chloranilic acid (CLA), as π electron acceptor. The CTC was characterized using different spectroscopic and thermogravimetric techniques. UV–visible spectroscopy ascertained the formation of the CTC in methanol via formation of a new broad absorption band with maximum absorption peak (λmax) at 530 nm. The molar absorptivity (ε) of the complex was 3.33 × 103 L mol−1 cm−1 and its band gap energy was 1.91 eV. The stoichiometric ratio of REM:CLA was found to be 1:1. The association constant of the complex was 1.11 × 109 L mol−1, and its standard free energy was 5.16 × 104 J mole−1. Computational calculation for atomic charges of energy minimized REM was conducted, the site of interaction on REM molecule was assigned and the mechanism of the reaction was postulated. The solid-state CTC was further characterized by FT-IR and 1H NMR spectroscopic techniques. Both FT-IR and 1H NMR confirmed the formation of the CTC and its structure. The reaction was adopted as a basis for developing a novel 96-microwell spectrophotometric method (MW-SPA) for REM. The assay limits of detection and quantitation were 3.57 and 10.83 µg/well, respectively. The assay was validated, and all validation parameters were acceptable. The assay was implemented successfully with great precision and accuracy to the determination of REM in its bulk form and pharmaceutical formulation (injection). This assay is simple, economic, and more importantly, has high throughput property. Therefore, the assay can be valuable for routine in quality control laboratories for analysis of REM's bulk form and pharmaceutical injection.

Exceptional electromagnetic radiation shielding performance and dielectric properties of surfactant assisted polypyrrole-carbon allotropes composites

The present work reports the development of composites of surfactant assisted Polypyrrole incorporated with three different carbon allotropes that are Amine Functionalized Multiwalled Carbon Nanotubes, Graphene and Hybrid Carbon Assemblage by in-situ emulsion polymerization of Pyrrole monomer with Sodium Lauryl sulphate as dopant. The prepared composites were characterized by different techniques. Spectroscopic analysis demonstrates that the presence of Graphene, Amine Functionalized Multiwalled Carbon Nanotubes and Hybrid carbon structures facilitates strong polarization due to the formation of a solid-state charge-transfer complex between Polypyrrole and Carbon Allotropes. This provides appropriate impedance matching and superior dipole interaction, which leads to the high microwave absorption properties. Exceptional Electromagnetic Radiation shielding measurement of the composites in Ku-band shows a shielding attenuation from − 28.8 dB to − 79.9 dB. Based on obtained results, polypyrrole-carbon allotropes composites can be utilized as effective shield materials for electromagnetic noise signals and electronic packaging of high tech equipments. Furthermore, the obtained high values of dielectric properties suggest that the prepared composites can be used for stealth technology.

Synthesis of reduced graphene oxide-conducting polymers-Co3O4 composites and their excellent microwave absorption properties

In this work, novel ternary composites consisting of reduced graphene oxide, conducting polymers (polyaniline, polypyrrole and poly (3,4-ethylenedioxythiophene)) and Co3O4 nanoparticles were successfully fabricated by a three-step method. The structure and morphology of the composites were characterized by FT-IR, XRD, XPS, TEM and Raman spectroscopy. The results showed that uniform Co3O4 nanoparticles with a diameter in the range of 5–10 nm were distributed on the surface of reduced graphene oxide-conducting polymers (RGO-CPs). The excellent microwave absorption properties of the ternary composites mainly originated from the dipole polarization, electronic spin and charge polarization of Co3O4 nanoparticles, the efficient complementarities between RGO-CPs and Co3O4 nanoparticles and the solid-state charge-transfer complex between RGO and CPs. The maximum reflection losses of reduced graphene oxide-polyaniline-Co3O4, reduced graphene oxide-polypyrrole-Co3O4 and reduced graphene oxide-poly (3,4-ethylenedioxythiophene)-Co3O4 are −44.5 dB, −43.5 dB and −46.5 dB, the absorption bandwidths with the reflection losses below −10 dB are 4.3 GHz, 6.4 GHz and 2.1 GHz with a thickness of 3.3 mm, 3.2 mm and 3.1 mm, respectively. Such excellent microwave absorption composites could be used as a new kind of candidate for the new types of microwave absorbing materials.

Nanostructured graphene/Fe3O4 incorporated polyaniline as a high performance shield against electromagnetic pollution

The development of high-performance shielding materials against electromagnetic pollution requires mobile charge carriers and magnetic dipoles. Herein, we meet the challenge by building a three-dimensional (3D) nanostructure consisting of chemically modified graphene/Fe3O4(GF) incorporated polyaniline. Intercalated GF was synthesized by the in situ generation of Fe3O4 nanoparticles in a graphene oxide suspension followed by hydrazine reduction, and further in situ polymerization with aniline to form a polyaniline composite. Spectroscopic analysis demonstrates that the presence of GF hybrid structures facilitates strong polarization due to the formation of a solid-state charge-transfer complex between graphene and polyaniline. This provides proper impedance matching and higher dipole interaction, which leads to the high microwave absorption properties. The higher dielectric loss (ε'' = 30) and magnetic loss (μ'' = 0.2) contribute to the microwave absorption value of 26 dB (>99.7% attenuation), which was found to depend on the concentration of GF in the polyaniline matrix. Moreover, the interactions between Fe3O4, graphene and polyaniline are responsible for superior material characteristics, such as excellent environmental (chemical and thermal) degradation stability and good electric conductivity (as high as 260 S m(-1)).

Simultaneous Reduction of Graphene Oxide and Polyaniline: Doping-Assisted Formation of a Solid-State Charge-Transfer Complex

We report the formation of a solid-state charge-transfer complex upon simultaneous reduction of a graphene oxide–polyaniline (GO-PANI) composite consisting of GO sheets coated by a thin layer of PANI. The reduced R(GO-PANI) material exhibits an unprecedented donor–acceptor interaction at the interface between RGO sheets and the thin PANI layer coating. A conceptual explanation is proposed in which RGO plays a dual role as electron acceptor and as large counterion stabilizing an atypical intermediate oxidation state of PANI. Moreover, the donor–acceptor interactions are responsible for superior materials characteristics, such as excellent water dispersibility, high environmental (chemical and thermal) degradation stability, and enhanced electric conductivity as high as 2600 S/m. These results may enable further opportunities for the development of novel electroactive materials based on graphene and intrinsically conducting polymers and the fabrication of corresponding flexible electronic devices through traditional solution processing techniques.

Synthesis, spectrophotometric, structural and thermal studies of the charge transfer complex of p-phenylenediamine, as an electron donor with π acceptor 3,5-dinitrobenzoic acid

The interaction between p-phenylenediamine (PPD) as a donor with the pi acceptor 3,5-dinitrobenzoic acid (DNB) has been investigated spectrophotometrically in methanol at room temperature. CT complex formed as a result of transfer of lone pair of electrons and exhibits well resolved charge transfer bands in the regions where neither donor nor acceptor have any absorption. The stoichiometry of the charge transfer complex (CTC) was found to be 1:1. The solid state CTC has also been synthesized, and has been characterized by elemental analysis, FTIR spectra, (1)H NMR spectroscopy and electronic absorption. The thermal stability of CT complex was studies using TGA and DTA analyses techniques. On the basis of the studies, the structure of CT complex is [(PPD)(DNB)], and a general mechanism for its formation is proposed. The formation constant and other physical parameters of the CT complex were determined by the Benesi-Hildebrand equation.

Solid State 13C-NMR as an Indicator of the Microstructure of a Silicon Containing Dianhydride and Derived Bisimides

The CP/MAS 13C-NMR spectrum of bis(3,4-dicarboxyphenyl)-dimethylsilane dianhydride (SiDA) as well as the spectra of the N-methyl and N-n-propyl bisimides derived from this dianhydride confirm the occurrence of solid state charge transfer complex (CTC) formation in these compounds. The proposed solid state alignment for SiDA was confirmed by X-ray diffraction spectroscopy. These compounds are monomeric models for polyimides and CTC formation in them supports the probability that such complexes form in polyimides.

Stoichiometry and stability of some solid state charge transfer complexes formed in imidazole-hydrocarbon systems

The compositions of charge transfer complexes of imidazole with some aromatic hydrocarbons (naphthalene, anthracene, phenanthrene and biphenyl) were established through phase diagram studies. The enthalpies and entropies of fusion of these complexes were estimated by differential scanning calorimetry. The relative stabilities of the solid state charge transfer complexes in the donor-acceptor systems studied could not be predicted from the areas under the curves of the congruent compounds in the phase diagrams.

Iodine-incorporated polystyrene for laser marking

An iodine-incorporated polymeric film, based on a solid-state charge-transfer complex between polystyrene and iodine, is described. The material prepared, originally red, can be marked (changing to transparent) by an Ar+ laser beam. Possible photochemical and photothermal mechanisms for such transformation are proposed. The laser print can be erased by exposing the film to I2 vapor. Besides its use as a laser-beam diagnostic material, possible future applications include optical storage devices.

On the compositions and strengths of charge-transfer complexes

The compositions of charge-transfer complexes of urea and thiourea with some aromatic hydrocarbons (naphthalene, anthracene, phenanthrene and biphenyl) have been established through phase diagram studies. The enthalpies and entropies of fusion of these complexes have been estimated by differential scanning calorimetry. It is observed that the relative stabilities of the solid-state charge-transfer complexes in the donor-acceptor systems studied cannot be predicted from the areas under the curves of the congruent compounds in the phase diagrams.

Vibronic coupling in excited charge-transfer states of solid-state charge-transfer complexes

Symmetry properties of CT excited states of some weak donor-acceptor complexes are discussed in the context of vibronic coupling with intermolecular vibrations. The results are applied to the analysis of electroabsorption spectra of anthracene-PMDA.

Frequencies of intermolecular vibrations in electronically excited dimers and charge-transfer complexes in solids

Theoretical arguments are presented indicating that the intermolecular translational frequency in solid-state charge-transfer complexes and dimers decreases upon electronic excitation. These arguments are used to explain some features of the spectrum of solid anthracene—PMDA.