Organic Charge-transfer Complexes Research Articles

Intramolecular exciplex featuring a bis-sp3 C-locked acceptor-donor-acceptor sandwich.

Intramolecular exciplex systems featuring thermally activated delayed fluorescence (TADF) have garnered significant attention in the realm of organic light-emitting diodes (OLEDs). Nonetheless, the occurrence of organic sandwich intramolecular exciplexes remains rare due to structural limitations and synthetic challenges. Herein, we present a novel rigid acceptor-donor-acceptor (A-D-A) sandwich complex, dSFQP, characterized by two sp3 C-locking moieties. This compound exhibits TADF characteristics facilitated by a multiple through-space charge-transfer process. X-ray crystallographic analysis confirms the distinctive sandwich configuration. The parallel spatial arrangement and minimized A-D-A configuration enhance electronic interactions, resulting in a high photoluminescence quantum yield, rapid reverse intersystem crossing rate, and sluggish nonradiative decay rate. OLEDs employing dSFQP as the dopant achieve a maximum external quantum efficiency (EQE) of 28.5% with a low efficiency roll-off of merely 2.8% at 1000 cd m-2. Even at a high brightness of 10 000 cd m-2, the EQE remains notably high at 17.5%. Our current results provide an effective way to further innovate the design of new organic charge-transfer complexes.

Polar Organic Charge-Transfer Complex of the Asymmetrical Component for Flexible Piezoelectric Energy Harvesting and Self-Powered Wearable Sensors.

Organic piezomaterials have attracted much attention because of their easy processing, lightweight, and mechanic flexibility properties. Developing new smart organic piezomaterials is highly required for new-generation electronic applications. Here, we found a novel organic piezomaterial of organic charge-transfer complex (CTC) consisting of dibenzcarbazole analogue (DBCz) and tetracyanoquinodimethane (TCNQ) in the molecular-level heterojunction stacking mode. The DBCz-TCNQ complex exhibited ferroelectric properties (the saturated polarization of ∼1.23 μC/cm2) at room temperature with a low coercive field. The noncentrosymmetric alignment (Pc space group) led to a spontaneous polarization of this architecture and thus was the origin of the piezoelectric behavior. Lateral piezoelectric nanogenerators (PENGs) based on the thermal evaporated CTC thin-film exhibited significant energy conversion behavior under mechanical agitation with a calculated piezoelectric coefficient (d31) of ∼33 pC/N. Furthermore, such a binary CTC thin-film constructed single-electrode PENG could show steady-state sensing performance to external stimuli as this flexible wearable device precisely detected physiological signals (e.g., finger bending, blink movement, carotid artery, etc.) with a self-powered supply. This work provides that the polar CTCs can act as efficient piezomaterials for flexible energy harvesting, conversion, and wearable sensing devices with a self-powered supply, enabling great potential in healthcare, motion detection, human-machine interfaces, etc.

(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

New Organic Crystalline Material Close to Nodal-Line Materials: α′-STF2IBr2

Recently, topological materials (TMs) have attracted attention from various scientists. Their electronic properties are governed by relativistic particles called Dirac fermions which, in some cases, possess no masses and move in solids with the speed of light. In addition to the unique particles, such materials exhibit unprecedented electronic properties because of the quantum effects (interference between wavefunctions). Examples include nodal-line materials (NLMs), where metallic or even superconducting properties may appear only at the surface of the single crystals of insulators. Thus far, whether they be organic or inorganic compounds, TMs have hardly been discovered except for the zero-gap conductors (ZGCs), because there is no guideline on how to develop such unusual materials. In this work, we prepared a new organic charge–transfer complex, α′-STF2IBr2 (STF = bis(ethylenedithio)diselenadithiafulvalene), which measured the electrical and magnetic properties and calculated the band structure and intermolecular interactions. A close comparison with those of α-STF2I3, being established as a ZGC at p > 12–15 kbar, revealed that α′-STF2IBr2 is also closely related to it, but belongs to a different type of TMs, namely NLMs. This finding will accelerate the successive findings of NLMs to elucidate the mechanism of their unique electronic properties.

Synthesis, spectrophotometric, pharmacology and theoretical investigation of a new electron transfer complex of 8-hydroxyquinoline with oxalic acid in different polar solvents

Preparation, characterization, and investigation of a novel organic charge transfer (CT) complex were carried out, with a focus on exploring its antibacterial and antifungal characteristics. Theoretical analysis backs up the experimental findings. CT complex formed was synthesized between 8-hydroxyquinoline (8HQ) and oxalic acid (OA) at RT (room temperature). Different analyses were used to describe the CT complex, including 1H-NMR, FTIR, TGA/DTA, and UV-vis spectra (in different solvents). These indicate that the CT interaction is linked to proton transfer from OA to 8HQ and the subsequent development of ‘N+__H…O-“ type bonding. On the basis of wave number, the CT complex and reactants are distinguished in FTIR spectra. By using Thermo gravimetric Analysis/Differential Thermal Analysis (TGA/DTA) tests, the thermal stability of complicated and thorough corrosion was examined. Through UV-visible spectroscopy, physical characteristics like ECT (interaction energy), RN (resonance energy), ID (ionization potential), f (oscillator strength) and ΔG (free energy) were calculated. The εCT (molar extinction coefficient), the KCT (formation constant), and additional physical properties of this complex were calculated by the Benesi-Hildebrand equation in order to determine its 1:1 stoichiometry. The biological properties are also supported by theoretical study. The protein, Human Serum Albumin (HSA), is observed to bind with CT complex, as shown by molecular docking and the observed binding energy value is −167.04 kcal/mol. Molecular dynamics (MD) simulation 100 ns run was used to refine docking results and binding free energy was calculated using MM-PBSA. This study introduces a novel CT complex, offering fresh perspectives on molecular interactions. Communicated by Ramaswamy H. Sarma

Solid-state green synthesis of blue light emitting fluorescent novel organic charge transfer complex; its optical, physicochemical and thermal studies

A novel charge transfer complex (HMBAA) using 3-hydroxy-4-methoxy benzaldehyde (HMB) and anthranilic acid (AA) has synthesized via green synthesis using solid-state grinding method. The phase diagram study has been employed to identify the exact composition forming the charge transfer (CT) complex. To study the various thermal properties of the novel complex, the enthalpy of fusion values of CT complex and parents are obtained from their DSC curves. The sharp and single endothermic melting peak of CT complex at very high temperature signifies the successful synthesis of the CT complex and its pure nature. The FTIR, NMR and PXRD studies infers the structural changes and novelty of CT complex. The study of cyclic voltammetry shows the redox behaviour of the CT complex. The optical absorption, emission and the CIE chromaticity diagram studies reveal the remarkable fluorescent emission properties of the novel CT complex in the deep blue region which indicates the utility of CT complex for its future applicability as fluorescence and pharmaceutical material. Nevertheless, the reported study is an opening for the solid-state grinding green synthesis method for synthesizing the worth novel materials.

Organic charge-transfer complex induces chemoselective decarboxylation to aryl radicals for general functionalization

Organic charge-transfer complex induces chemoselective decarboxylation to aryl radicals for general functionalization

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.

Cation‐Anion Redox Active Organic Complex for High Performance Aqueous Zinc Ion Battery

Organic redox compounds are attractive cathode materials in aqueous zinc‐ion batteries owing to their low cost, environmental friendliness, multiple‐electron‐transfer reactions, and resource sustainability. However, the realized energy density is constrained by the limited capacity and low voltage. Herein, copper‐tetracyanoquinodimethane (CuTCNQ), an organic charge–transfer complex is evaluated as a zinc‐ion battery cathode owing to the good electron acceptation ability in the cyano groups that improves the voltage output. Through electrochemical activation, electrolyte optimization, and adoption of graphene‐based separator, CuTCNQ‐based aqueous zinc‐ion batteries deliver much improved rate performance and cycling stability with anti‐self‐discharge properties. The structural evolution of CuTCNQ during discharge/charge are investigated by ex situ Fourier transform infra‐red (FT‐IR) spectra, ex situ X‐ray photoelectron spectroscopy (XPS), and in situ ultraviolet visible spectroscopy (UV–vis), revealing reversible redox reactions in both cuprous cations (Cu+) and organic anions (TCNQx‐1), thus delivering a high voltage output of 1.0 V and excellent discharge capacity of 158 mAh g−1. The remarkable electrochemical performance in Zn//CuTCNQ is ascribed to the strong inductive effect of cyano groups in CuTCNQ that elevated the voltage output and the graphene‐modified separator that inhibited CuTCNQ dissolution and shuttle effect in aqueous electrolytes.

Charge-transfer complex promotes energy storage performance of single-moiety organic electrode materials in aqueous zinc-ion battery at low temperatures

Charge-transfer organic materials are molecular metallic materials with high electronic conductivity, but their potential in rechargeable batteries, especially at low temperatures, has not been investigated. In this work, micro-structured organic charge-transfer complex tetrathiofluorene-7,7,8,8-tetroquinolinedimethane (TTF-TCNQ) is applied as cathode material in aqueous zinc-ion batteries (AZIBs). Ionic storage behavior of TTF–TCNQ complex is systematically investigated from 25 ℃ to −40 ℃. Owing to higher electrical conductivity and higher ionic diffusivity in ionic storage, smaller charge transfer resistance, and lower activation energy, TTF-TCNQ shows much superior rate and cycling performance than each single-moiety counterpart, especially at low temperatures. Reaction mechanism is explored by ex-situ X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier Transform infrared spectroscopy (FT-IR) and in-situ Raman technologies, confirming that CN and CS groups are the redox centers and the redox reaction is highly reversible. Our research not only provides a new type of choice for AZIBs at low temperatures, but also greatly broads the application field of charge-transfer complexes.

Macrocycle‐Based Crystalline Supramolecular Assemblies Built with Intermolecular Charge‐Transfer Interactions

AbstractSynthetic macrocycles have served as principal tools for supramolecular chemistry, have greatly extended the scope of organic charge transfer (CT) complexes, and have proved to be of great practical value in the solid state during the past few years. In this Minireview, we summarize the research progress on the macrocycle‐based crystalline supramolecular assemblies primarily driven by intermolecular CT interactions (a.k.a. macrocycle‐based crystalline CT assemblies, MCCAs for short), which are classified by their donor–acceptor (D‐A) constituent elements, including simplex macrocyclic hosts, heterogeneous macrocyclic hosts, and host–guest D‐A pairs. Particular attention will be focused on their diverse functions and applications, as well as the underlying CT mechanisms from the perspective of crystal engineering. Finally, the remaining challenges and prospects are outlined.

Macrocycle-Based Crystalline Supramolecular Assemblies Built with Intermolecular Charge-Transfer Interactions.

Synthetic macrocycles have served as principal tools for supramolecular chemistry, have greatly extended the scope of organic charge transfer (CT) complexes, and have proved to be of great practical value in the solid state during the past few years. In this Minireview, we summarize the research progress on the macrocycle-based crystalline supramolecular assemblies primarily driven by intermolecular CT interactions (a.k.a. macrocycle-based crystalline CT assemblies, MCCAs for short), which are classified by their donor-acceptor (D-A) constituent elements, including simplex macrocyclic hosts, heterogeneous macrocyclic hosts, and host-guest D-A pairs. Particular attention will be focused on their diverse functions and applications, as well as the underlying CT mechanisms from the perspective of crystal engineering. Finally, the remaining challenges and prospects are outlined.

Highly Luminescent and Semiconducting Supramolecular Organic Charge Transfer Complex Generated via H‐Bonding Interaction Pathway

AbstractThe construction of a charge transfer (CT) organic material with important electrical properties is demonstrated where the charge transfer state is generated via delocalization through H‐bonding interaction pathway. The reaction of simple organic molecule pyromellitic acid with orthophenylene diamine in 1:2 ratios gives a colorless cocrystal 1’. The rare transition phenomena of a colorless cocrystal 1’ to an orange charge transfer state 1 take place in methanol water media over several days. The charge transfer state is isolated as orange single crystals of 1 which show semiconducting as well as fluorescent properties. The X‐ray diffraction analysis of 1 demonstrates the formation of charge separated extended H‐bonded network which is supposed to be solely responsible for the delocalization of charge in the system. This is the first example of formation of donor–acceptor‐based charge transfer material constructed by just tuning the H‐bond distance of a colorless cocrystalline state with non‐chalcogen and non‐halogenated molecules.

Recent Advances in Cartesian-Grid DFT in Atoms and Molecules.

In the past several decades, density functional theory (DFT) has evolved as a leading player across a dazzling variety of fields, from organic chemistry to condensed matter physics. The simple conceptual framework and computational elegance are the underlying driver for this. This article reviews some of the recent developments that have taken place in our laboratory in the past 5 years. Efforts are made to validate a viable alternative for DFT calculations for small to medium systems through a Cartesian coordinate grid- (CCG-) based pseudopotential Kohn–Sham (KS) DFT framework using LCAO-MO ansatz. In order to legitimize its suitability and efficacy, at first, electric response properties, such as dipole moment ( μ ), static dipole polarizability ( α ), and first hyperpolarizability ( β ), are calculated. Next, we present a purely numerical approach in CCG for proficient computation of exact exchange density contribution in certain types of orbital-dependent density functionals. A Fourier convolution theorem combined with a range-separated Coulomb interaction kernel is invoked. This takes motivation from a semi-numerical algorithm, where the rate-deciding factor is the evaluation of electrostatic potential. Its success further leads to a systematic self-consistent approach from first principles, which is desirable in the development of optimally tuned range-separated hybrid and hyper functionals. Next, we discuss a simple, alternative time-independent DFT procedure, for computation of single-particle excitation energies, by means of “adiabatic connection theorem” and virial theorem. Optical gaps in organic chromophores, dyes, linear/non-linear PAHs, and charge transfer complexes are faithfully reproduced. In short, CCG-DFT is shown to be a successful route for various practical applications in electronic systems.

Efficient modeling of organic adsorbates on oxygen-intercalated graphene on Ir(111)

Organic charge transfer complexes (CTCs) can be grown as thin films on intercalated graphene (Gr). Deciphering their precise film morphologies requires global ab initio structure search, where configurational sampling is computationally intractable unless we reconsider the model for the complex substrate. In this study, we employ charged freestanding Gr to approximate an intercalated Gr/O/Ir(111) substrate, without altering the adsoption properties of deposited molecules. We compare different methods of charging Gr and select the most appropriate substitute model for Gr/O/Ir(111) that maintains the adsorption properties of fluorinated tetracyanoquinodimethane (${\mathrm{F}}_{4}\mathrm{TCNQ}$) and tetrathiafulvalene (TTF), prototypical electron acceptor/donor molecules in CTCs. Next, we apply our model in the Bayesian optimization structure search method and density-functional theory to identify the stable structures of ${\mathrm{F}}_{4}\mathrm{TCNQ}$ and TTF on supported Gr. We find that both molecules physisorb to Gr in various configurations. The narrow range of adsorption energies indicates that the molecules may diffuse easily on the surface and molecule-molecule interactions likely have a central role in film formation. Our study shows that complex intercalated substrates may be approximated with charged freestanding Gr, which can facilitate exhaustive structure search of CTCs.

Two New Organic Co-Crystals Based on Acetamidophenol Molecules

Herein we present two new organic co-crystals obtained through a simple solution growth process based on an acetamidophenol molecule, either paracetamol or metacetamol, and on 7,7,8,8-tetracyanoquinodimethane (TCNQ). These co-crystals are part of a family of potential organic charge transfer complexes, where the acetamidophenol molecule behaves as an electron donor and TCNQ behaves as an electron acceptor. Due to the sub-micron size of the crystalline domains, 3D electron diffraction was employed for the structure characterization of both systems. Paracetamol-TCNQ structure was solved by standard direct methods, while the analysis of metacetamol-TCNQ was complicated by the low resolution of the available diffraction data and by the low symmetry of the system. The structure determination of metacetamol-TCNQ was eventually achieved after merging two data sets and combining direct methods with simulated annealing. Our study reveals that both paracetamol-TCNQ and metacetamol-TCNQ systems crystallize in a 1:1 stoichiometry, assembling in a mixed-stack configuration and adopting a non-centrosymmetric P1 symmetry. It appears that paracetamol and metacetamol do not form a strong structural scaffold based on hydrogen bonding, as previously observed for orthocetamol-TCNQ and orthocetamol-TCNB (1,2,4,5-tetracyanobenzene) co-crystals.

Exploring Interaction Dynamics of Designed Organic Charge Transfer Complex of 6-Aminoindole and Chloranilic Acid: Spectrophotometric, Characterization, Computational, Antimicrobial, and DNA Binding Properties

The chemistry of a new charge and proton transfer hydrogen bonded complex (PT CT) between the donor 6-Aminoindole (6 AMI) and the π-acceptor Chloranilic acid (CLA) has been explored in acetonitrile (ACN), methanol (MeOH), and 50% acetonitrile + 50% methanol (ACN-MeOH) at 25 °C by using electronic absorption spectroscopy. By exploiting Job's and the photometric titration methods, the molar proportion of the PT CT complex was confirmed as 1:1. The modified Benesi-Hildebrand principle was used to evaluate the association constant (KCT) and molar absorptivity (ƐCT) of the PT CT complex, and these values indicate that the produced PT CT complex is more stable. In three different solvents, the effect of solvent polarity on charge transfer spectra was also observed. Different spectroscopic physical parameters were assessed in different polar solvents, including energy (ECT), ionization potential (ID), resonance energy (RN), oscillator strength (f), dissociation energy (W), standard gibbs free energy (ΔGo), transition dipole movement (μEN), and these were also within the accepted values, confirming the stability of the formed PT CT complex. The produced solid PT CT complex was analyzed by using FT-IR, NMR, TGA-DTA, and SEM-EDX spectra. Powder XRD analysis was used to determine the PT CT complex nature and crystalline size. The biological activity of the current PT CT complex has been screened in antimicrobial and DNA binding studies. The synthesized PT CT complex was shown to have excellent antimicrobial activity and DNA binding affinity. Therefore, in the future, it may be used as a pharmaceutical drug for bacterial and fungal infections. The computational studies were carried out by using DFT analysis, and the functions were used to B3LYP and CAM B3LYP in the gas phase, with the basis set being 6-31G + (d, p). The bond lengths, bond angles, Mulliken atomic charges, MEP maps, reactivity parameters, and FMO surfaces were also calculated. The computational analysis is additionally supported by the experimental studies of the PT CT complex.

Organic charge transfer complex at the boundary between superconductors and insulators: critical role of a marginal part of the conduction pathways

We have found that the electrical properties of an organic charge transfer salt are qualitatively affected by slight differences in the conformation of one of the ethylene groups, which is not involved in the conduction pathways.

Pharmacological and quantum chemical studies of 2-aminobenzo[d]thiazol-3-ium 4-chlorobenzenesulphonate: Synthesis, spectral, thermal analysis and structural elucidation

The organic charge transfer complex 2-aminobenzo[d]thiazol-3-ium 4-chlorobenzenesulphonate (2ABT4CBS) was synthesized and grown as single crystals by slow solvent evaporation method at room temperature. Single crystal X-ray diffraction results revels that 2ABT4CBS crystallized into a monoclinic crystal system with space group P21/c. The molecular structure and functional groups were analyzed by spectral studies such as 1H and 13C NMR, UV–Visible and FT-IR. Thermal stability of the compound was determined by TG and DTAanalysis. DFT was used in the calculation of the frontier molecular orbital (FMO), Mulliken load distribution and thermodynamic properties by employing B3LYP/6-31G (d,p) and HF/6-31G levels of theory. The results of the DNA binding demonstrate that the synthesized compound 2ABT4CBS interacts with CT-DNA in a considerable way. The antioxidant capabilities of 2ABT4CBS were also analyzed against DPPH radical and excellent radical scavenging abilities were identified. Molecular docking studies with PDB: 1BNA, clearly suggested that synthesized compound show binding affinity to the minor groove and established hydrogen bonding with DA5 of CT-DNA.

Giant power factor and high air stability in an n-type metal–organic charge-transfer complex

We report an n-type metal–organic complex (Br–C6H4–NH2)2CuBr2. This substance uniquely combines giant power factor, ultrahigh electrical conductivity, high electron mobility, remarkable air stability, easy synthesis, and cheap laboratory procedures.