Hydrogen-bonded Charge-transfer Complexes Research Articles

Synthesis, spectroscopic characterization, DNA binding and DFT/PCM calculations of new Hydrogen-bonded charge transfer complex between 4-dimethylaminopyridine and Chloranilic acid

A charge transfer hydrogen bonded complex between the electron donor 4-dimethylaminopyridine (4-DMAP) and the electron acceptor Chloranilic acid (CLA) has been synthesized. The complex was studied experimentally and theoretically. A chemical reaction developed due to strong H-bonding, followed by proton transfer from the CLA to the 4-DMAP in acetonitrile medium (ACN). The straight line approach was employed to verify the 1:1 M ratio of the synthesised CT complex. The Benesi-Hildebrand equation was employed to compute the association constant (KCT), molar absorptivity (εCT), and other physical parameters. The synthesized complex was characterized spectroscopically. The presence of proton and charge transfers in the resultant complex was supported by 1H NMR, FT-IR and SEM-EDX investigations. The complex DNA binding ability of complex was investigated using electron absorption spectroscopy to reveal that the CT complex binding mechanism is intercalative and the intrinsic binding constant (Kb) value is 6.7 × 104 M−1. Theoretical calculations using DFT at the basis set CAM-B3LYP/6–31 G (d, p) were used to validate the experimental outcomes. The Mullikan atomic charges, geometrical parameters, and molecular electrostatic potential maps (MEPs) were computed and interpreted in conformity with the experimental results. In addition to e-transfer, the presence of an H-bond influences complex stability. There is good agreement between experimental results and DFT calculations.

Diphenoquinhydrones and Related Hydrogen-Bonded Charge-Transfer Complexes.

Benzoquinone and hydroquinone cocrystallize to form quinhydrone, a 1:1 complex with a characteristic structure in which the components are positioned by hydrogen bonds and charge-transfer interactions. We have found that analogous diphenoquinhydrones can be made by combining 4,4'-diphenoquinones with the corresponding 4,4'-dihydroxybiphenyls. In addition, mixed diphenoquinhydrones can be assembled from components with different substituents, and mismatched quinhydrones can be made from benzoquinones and dihydroxybiphenyls. In all cases, the components of the resulting structures are linked in alternation by O-H···O hydrogen bonds to form essentially planar chains, which stack to produce layers in which π-donors and π-acceptors are aligned by charge-transfer interactions. Geometric parameters, computational studies, and spectroscopic properties of diphenoquinhydrones show that the key intermolecular interactions are stronger than those in simple quinhydrone analogues. These findings demonstrate that the principles of modular construction underlying the formation of classical quinhydrones can be generalized to produce a broad range of hydrogen-bonded charge-transfer materials in which the components are positioned by design.

Synthesis, spectroscopic and computational studies on hydrogen bonded charge transfer complex of duvelisib with chloranilic acid: Application to development of novel 96-microwell spectrophotometric assay

Duvelisib (DUV) is a is a small-molecule with inhibitory action for phosphoinositide 3-kinase (PI3K). It has been recently approved for the effective treatment of chronic lymphocytic leukemia (CLL) and small lymphocytic lymphoma (SLL). Novel charge transfer complex (CTC) between DUV, as electron donor, with chloranilic acid (CLA), as π electron acceptor has been synthesized and characterized using different spectroscopic and thermogravimetric techniques. UV–visible spectroscopy ascertained the formation of the CTC in different solvents of varying polarity indexes and dielectric constants via formation of new broad absorption band with maximum absorption peak (λmax) in the range of 488–532 nm. The molar absorptivity of the CTC was dependent on the polarity index and dielectric constant of the solvent; the correlation coefficients were 0.9955 and 0.9749, respectively. The stoichiometric ratio of DUV:CLA was 1:1. Electronic spectral analysis was conducted for characterization of the complex in terms of its electronic constants. Computational calculation for atomic charges of energy minimized DUV was conducted and the site of interaction on DUV molecule was assigned. The solid-state CTC of DUV:CLA (1:1) was synthesized, and its structure was characterized by UV–visible, mass, FT-IR, and 1H NMR spectroscopic techniques. Both FT-IR and 1H NMR confirmed that both CT and hydrogen bonding contributed to the molecular composition of the complex. The reaction was adopted as a basis for developing a novel 96-microwell spectrophotometric assay (MW-SPA) for DUV. The assay limits of detection and quantitation were 0.57 and 1.72 µg/well, respectively. The assay was validated and all validation parameters were acceptable. The method was implemented successfully with great precision and accuracy to the analysis of the DUV in its bulk and capsules.

Interaction between Picric Acid and 5-aminoquinoline: A Theoretical Study

In the present work, density functional theory and time-dependent density functional theory were employed to investigate the hydrogen-bonded charge transfer complex of 5-aminoquinoline (5AQ) and picric acid (PA) at B3LYP/6-31G(d,p) level in the gas phase as well as CHCl\(_3\). The geometrical parameters, optimization energies, interaction energies, frontier molecular orbitals (FMOs), and ground-state dipole moment were considered, which supported the stability of the complex. Hence, the theoretical study of the 5AQ-PA complex provides valuable information about its molecular structure, possible interaction sites and electronically excited states.

Spectroscopic Characterization, Molecular Modeling and DFT/TD-DFT/PCM Calculations of Novel Hydrogen-Bonded Charge Transfer Complex between Chloranilic Acid and 2-Amino-4,6-Dimethylpyridine

A charge transfer hydrogen bonded complex between the electron donor (proton acceptor) 2-amino-4,6-dimethylpyridine with the electron acceptor (proton donor) chloranilic acid has been synthesized and studied experimentally and theoretically. The stability constant recorded high values indicating the high stability of the formed complex. In chloroform, ethanol, methanol and acetonitrile were found the stoichiometric ratio 1:1. The solid complex was prepared and characterized by different spectroscopy techniques. FTIR, 1H and 13C NMR studies supported the presence of proton and charge transfers in the formed complex. Complemented with experimental results, molecular modelling using the density functional theory (DFT) calculations was carried out in the gas, chloroform and methanol phases where the existence of charge and hydrogen transfers. Finally, a good consistency between experimental and theoretical calculations was found confirming that the applied basis set is the suitable one for the system under investigation.

Synthesis, Characterization, and Biological Evaluation of a New Hydrogen-Bonded Charge-Transfer Complex of 2-Amino-4-methoxy-6-methylpyrimidine

A new hydrogen-bonded charge-transfer (HB-CT) complex formed between the donor 2-amino-4-methoxy-6-methylpyrimidine (AMMP) and the π-acceptor 2,5-dihydroxy-p-benzoquinone (DHBQ) was investigated in both solid and solution states. The investigation was conducted using UV-Vis, CHN, FTIR, 1H NMR, XRD, and TG-DTA analyses. The molecular composition of the CT complex in MeOH was found to be 1 : 1. The formation constant (KCT), molecular extinction coefficient (ε), and several other spectroscopic physical parameters were evaluated at different temperatures. The thermodynamic properties of the CT interaction in MeOH were studied by calculating the enthalpy (ΔH°), entropy (ΔS°), and free energy (ΔG°). The thermodynamic parameters indicated that van der Waals interactions and hydrogen bonding occur between AMMP and DHBQ in MeOH. The CHN, FTIR, and TG-DTA measurements confirmed that the solid HB-CT complex forms in a 2 : 1 ratio, i.e., [(AMMP)2(DHBQ)], and exhibits high stability. Moreover, XRD analysis was used to establish that the mean particle size of the complex is 23 nm. Finally, the solid HB-CT complex was screened for its antibacterial, antifungal, and antioxidant activities. It shows good activity against various bacterial and fungal species. Furthermore, the HB-CT complex exhibits good DPPH scavenging activity.

Spectroscopic and spectrophotometric studies on hydrogen bonded charge transfer complex of 2-amino-4-methylthiazole with chloranilic acid at different temperatures

The synthesized hydrogen bonded charge transfer (CT) complex between 2-amino-4-methylthiazole (AMT) and chloranilic acid (CLA) was characterized using various spectral techniques such as UV–visible, FTIR, 1H NMR, ESI-MS, P-XRD and TG/DTA analysis. The CT complexes act as an intermediate in a variety of reactions involving electron rich and electron deficient molecules. The spectral analysis of the CT complex suggests that N and NH2 groups play a major role in determining the orientation in the reaction mechanism. The fluorescence studies show that Ct-DNA interacted with CT complex and quenched its intrinsic fluorescence in a static quenching process. Stern-Volmer equation was used to determine the binding ability of the CT complex with in vitro calf thymus DNA. The different physical parameters such as the association constant (KCT), molar extinction coefficient (ε), energy of interaction (ECT), ionization potential (ID), resonance energy (RN), free energy (∆G), oscillator strength (f) and transition dipole moment (μEN) were determined using Benesi-Hildebrand equation. The Van't Hoff equation was used to calculate the various thermodynamic parameters such as enthalpy (ΔH), entropy (ΔS) and free energy (ΔG). The nature of interaction between donor and acceptor moieties can also be visualized by calculating thermodynamic parameters. The molecular interaction between AMT and CLA has been established through N+—H∙∙∙∙O– hydrogen bonding. The straight line method was established by the 1:1 stoichiometry of the CT complex. TG/DTA analysis provided information about changes in material properties as a function of temperature. The various fragmentation of the CT complex was evaluated using ESI-mass spectroscopy.

Electronic spectral studies and DFT computational analysis of hydrogen bonded charge transfer complexes between chloranilic acid and 2,5-dihydroxy-p-benzoquinone with 2-amino-4-methylbenzothiazole in methanol

Two new hydrogen bonded charge transfer complexes between two electron acceptors (hydrogen bond donors), chloranilic acid (CA) and 2,5-dihydroxybenzoquinone (DHBQ) with an electron donor (hydrogen bond acceptor) 2-amino-4-methylbenzothiazole (AMBTZ) have been experimentally and theoretically studied in methanol. The measured electronic spectra of these two complexes, CA-AMBTZ and DHBQ-AMBTZ, were characterized by new absorption bands appearing at λmax of 529 and 489nm, respectively. The molecular compositions of the formed complexes were determined using Job and photometric titration methods to be 1:1. Furthermore, the formation constants and some spectroscopic physical parameters were determined. These revealed the formation of stable complexes and that CA-AMBTZ is more stable than DHBQ-AMBTZ. Using the B3LYP/6-31++ G(d,p) method, the geometries of CA, DHBQ, AMBTZ, CA-AMBTZ and DHBQ-AMBTZ were calculated in the gas phase and in methanol. In AMBTZ, the S and N (ring) atoms act as sites that can accept a proton from CA or DHBQ. In both complexes, the proton from CA or DHBQ was preferentially transferred to the ring N-atom of AMBTZ. Geometrical and reactivity parameters, molecular electrostatic potential (MEP) maps and natural atomic charges were computed and analyzed. The time-dependent density functional theory (TD-DFT) method has been applied to explain the origin of the electronic spectra. Natural bond orbital (NBO) analysis at the same level of the theory has been applied to shed more light on the origin of the charge transfer in the investigated complexes. The theoretical results obtained in this study proved highly consistent with the experimental ones.

Synthesis, single-crystal, DNA interaction, spectrophotometric and spectroscopic characterization of the hydrogen-bonded charge transfer complex of 2-aminopyrimidine with π-acceptor chloranilic acid at different temperature in acetonitrile

The charge transfer (CT) interaction of 2-aminopyrimidine (AP) with chloranilic acid (CLA) as π-acceptor was investigated spectrophotometrically in acetonitrile at different temperatures in the range of 25–50°C. The 1:1 stoichiometry of the synthesized CT complex was detected using straight line method. Benesi–Hildebrand equation was used to determine the association constant (KCT), molar extinction coefficient (ε) and other physical parameters. Various thermodynamics parameters such as enthalpy (ΔH), entropy (ΔS) and free energy (ΔG) were determined using UV–Visible spectrophotometry in acetonitrile at different temperatures. 1H NMR, FTIR, ESI-MS, elemental analyses, and UV–Visible techniques were used to characterize the hydrogen-bonded CT complex. 1H NMR spectroscopy was also used for the analysis of the CT complex where both hydrogen bond and charge transfer were present in its molecular composition. The interaction of the selected organic compound with Ct-DNA was well investigated using fluorescence spectroscopic method. Stern–Volmer constant (Ksv) was used to estimate the fluorescence quenching efficiency. Circular dichroism (CD) spectroscopy was employed to measure the conformational change of DNA in the presence of CT complex. Furthermore, the drug CT complex detected changes in its viscosity. The charge transfer complex was formed as a result of the transfer of the lone pair of electrons from donor to the acceptor and exhibits well resolved charge transfer bands in the regions where absorption by both donor and acceptor were absent. The thermal composition and stability of the CT complex were analyzed using thermogravimetric and differential thermal analysis (TGA and DTA) studies. The X-ray crystal structure was used for the interpretation of the structure of the [(AP)+ (CLA)−] CT complex. The crystal structure indicated that cation and anion are linked through strong N+H----O− type of hydrogen bond.

Spectroscopic characterisation and structural modelling of new hydrogen-bonded charge transfer complex between picric acid and 3-aminoquinoline

ABSTRACTNew charge transfer hydrogen-bonded (HBCT) complex between the electron donor 3-aminoquinoline with the electron acceptor picric acid has been synthesised and characterised experimentally and theoretically using a variety of physicochemical techniques. The experimental work included the use of UV–vis, IR and 1H NMR studies to characterise the complex in different hydrogen-bonded solvents. The studied reaction proceeded based on 1:1 stoichiometric ratio and the stability constant recorded high values. The solid complex was prepared and characterised by elemental analysis that confirmed its formation in 1:1. Both IR and NMR studies supported the existence of proton and charge transfers in the formed complex. In complemented with experimental results, molecular modelling using DFT using 31–6G(d,p) basis set was carried out in the gas phase where the existence of both charge and hydrogen transfers was reconfirmed in the obtained complex in full consistency with experimental results.

Synthesis, spectral studies and DFT computational analysis of hydrogen bonded-charge transfer complex between chloranilic acid with 2,4-diamino-quinoline-3-carbonitrile in different polar solvents

Abstract New hydrogen bonded charge transfer complex (HBCT) between 2,4-diamino-quinoline-3-carbonitrile (DAQC) and chloranilic acid (CA) is synthesized and characterized experimentally and theoretically. The experimental work included the use of electronic and vibrational spectra to analyze the formed complex. Based on electronic spectra, the molecular composition was determined by Jobs and molar ratio methods in different polar solvents included acetonitrile (AN), methanol (MeOH) and ethanol (EtOH). It was found to be 1:1 (donor:acceptor) in the different solvents. Also, the formation constant of the formed complex was determined using Benesi-Hildebrand equation where it recorded high values suggesting the high stability of the formed HBCT complex. The stability of the investigated complex was further analyzed by determining different spectroscopic parameters as oscillator strength, transition dipole moment, charge transfer energy, ionization potential, dissociation energy and free energy. The solid complex was synthesized and characterized by elemental analyses where 1:1 complex is formed. The infrared spectra revealed the existence of both charge transfer and hydrogen bonding in the formed complex which is responsible for its high stability. In order to complement the experimental work, two DFT methods, B3LYP and CAM-B3LYP were used to predict the stability, molecular structure, electronic and spectroscopic properties of the studied systems. These methods were introduced, for the first time, to study the stability of the expected structures of CA conformers. The one with lower energy (high stability) included two hydrogen bonding between CA hydroxyls and neighboring carbonyl groups. Of the suggested interaction complexes between chloranilic acid (CA) and 2,4-diamino-quinoline-3-carbonitrile (DAQC), the most stable one which has the lowest energy was used to simulate the observed electronic and vibrational spectra of the CA-DACQ complex. The reactivity descriptors indicated that DAQC is the e-donor while CA is e-acceptor. Also, the most reactive electrophilic and nucleophilic sites of CA and DAQC were predicted using the molecular electrostatic potential (MEP) map. Both experimental and theoretical studies confirmed the high stability of the formed complex based on the presence of charge transfer beside proton transfer in the CA-DAQC complex.

Proton-Coupled Electron Transfer in a Hydrogen-Bonded Charge-Transfer Complex.

A proton-coupled electron transfer (PCET) reaction in a hydrogen-bonded charge-transfer (CT) complex of 4-([2,2'-bipyridin]-4-yl)phenol (bpy-phenol) with a F- ion has been investigated by ultrafast time-resolved transient absorption spectroscopy. The phenolic receptor molecule, bpy-phenol, binds to the F- ion through a hydrogen bond and senses the F- ion via the Stokes-shifted CT band. Upon photoexcitation, CT from the phenol residue to the bpy residue promotes proton transfer from the phenol radical cation (ArOH•+) to the fluoride ion at ultrafast time scales of <150 fs (instrument response function limited) and 3 ps, separately. The fast and slow proton-transfer times are linked to two different types of hydrogen-bonding networks between the phenol residue and fluoride ion. Crystalline water in the fluoride salt hydrates mediates the proton-transfer reaction. This work demonstrates the participation of a hydrogen-bonded water bridge within a PCET reaction in a water-restricted environment.

Synthesis, spectroscopic and DFT theoretical studies on the hydrogen bonded charge transfer complex of 4-aminoquinoline with chloranilic acid

New charge transfer hydrogen bonded complex between the electron donor 4-aminoquinoline (4AQ) with the π acceptor chloranilic acid (CLA) has been synthesized and characterized using a variety of physico-chemical techniques. Experimental work included the use of UV–vis spectroscopy to recognize of the complex formation in different solvents included acetonitrile (AN), methanol (MeOH) and ethanol (EtOH) through the appearance of new broad absorption band with λmax in the 500–550nm region. Photometric titration and Job's methods of continuous variations were carried out to shed more light about the molecular composition of the formed complex in solution where 1:1 (donor:acceptor) complex was obtained. Electronic spectral data were further analyzed in terms of formation constant, molar extinction coefficient, spectroscopic and analytical parameters of the formed complex. The solid 1:1 complex was synthesized and its molecular structure was characterized by elemental analysis where 1:1 (donor:acceptor) complex was produced, in agreement with that in different solvents. NMR and IR spectroscopy were used for further analysis of the solid complex where both hydrogen bond and charge transfer were evident in its molecular composition. The experimental studies were complemented by quantum chemical calculations at DFT/B3LYP level of theory. Electronic structure was investigated by TD-DFT method and the description of frontier molecular orbitals and the location of electron density were introduced. It has been confirmed that stability of the formed complex arises from charge transfer and hydrogen bonding interactions in the complex structure. Furthermore, the TD-DFT showed that the experimentally characterized broad absorption band of the complex is a combination of two electronic transitions at 476 and 650nm of π-π⁎ and n-π⁎, respectively. In addition, the red shift of λmax of the complex compared with the reactants confirming the strengthening of the formed OH…N in the excited state.

Synthesis, spectroscopic characterization and structural investigation of a new charge transfer complex of 2,6-diaminopyridine with 4-nitrophenylacetic acid: Antimicrobial, DNA binding/cleavage and antioxidant studies

A new hydrogen-bonded charge-transfer complex (CT) formed by the reaction between donor, 2,6-diaminopyridine and acceptor, 4-nitrophenylacetic acid in methanol at room temperature. The crystal was characterized by elemental analysis, IR, NMR spectroscopic studies and thermal studies. The elemental analysis of CT complex, obtained data revealed that the formation of 1:1 ratio CT complex was proposed. Infrared and NMR studies confirm the chemical constituents and molecular structure of the synthesized complex crystal. The high thermal stability is due to the molecular frame work through H-bonding interactions. Structural investigation indicates that cation and anion are linked through strong N+–H⋯O− type of hydrogen bond. The hydrogen bonded charge transfer crystal was screened for its pharmacology, such as antimicrobial, DNA binding/cleavage and antioxidant studies. The CT complex was screened for its antibacterial and antifungal activity against various bacterial and fungal species, which shows good antimicrobial activity. The DNA binding results indicated that the compound could interact with DNA through intercalation. It should have weak to moderate capacity of scavenging with DPPH.

Tetrapeptide-coumarin conjugate 3D networks based on hydrogen-bonded charge transfer complexes: gel formation and dye release.

Oligopeptide-based derivatives are important synthons for bio-based functional materials. In this article, a Gly-(L-Val)-Gly-(L-Val)-coumarin (GVGV-Cou) conjugate was synthesized, which forms 3D networks in ethanol. The gel nanostructures were characterized by UV-vis spectroscopy, FT-IR spectroscopy, X-ray diffraction (XRD), SEM and TEM. It is suggested that the formation of charge transfer (CT) complexes between the coumarin moieties is the main driving force for the gel formation. The capability of the gel to encapsulate and release dyes was explored. Both Congo Red (CR) and Methylene Blue (MB) can be trapped in the CT gel matrix and released over time. The present gel might be used as a functional soft material for guest encapsulation and release.

Synthesis, characterization and pharmacological investigation of a new charge-transfer complex of 3-aminopyridinum-p-toluenesulfonate

The hydrogen-bonded charge-transfer complex, 3-aminopyridinum-p-toluenesulfonate was formed by the reaction between 3-aminopyridine and p-toluenesulfonic acid. On the basis of various spectroscopic results, the molecular structure has been confirmed. The crystal structure was deduced by single crystal X-ray diffraction analysis which indicated that cation and anion are linked through strong N+H---O− type of hydrogen bond. The hydrogen bonded charge transfer crystal was screened for its pharmacology, such as microbial, DNA binding/cleavage and antioxidant activity. The antibacterial and antifungal activities of the synthesized complex were examined against various bacteria and fungi strains, which showed a poor antibacterial and antifungal activity compared with standard antibacterial and fungal species. The DNA binding results indicated that the complex could interact with DNA through intercalation. The cleavage of the complex with CT-DNA inferred that the effects of cleavage are dose dependent. Antioxidant studies of the complex showed the significant antioxidant activity against DPPH, OH and ABTS radicals.

Hydrogen Bonded Charge Transfer Complex of Chloranilic Acid With Benzimidazole

The crystal structure of 1:1:1 complex of chloranilic acid with benzimidazole and water determined by X-ray diffraction methods is reported. It crystallizes in the monoclinic (space group, P21/c) crystal system. Both chloranilic acid and benzimidazole molecules adopt a face-to-face stacking arrangement along the b-axis. An interaction beween adjacent layers is a π...π stacking interactions between chloranilic acid molecules. The dihedral angle between the interacting chloranilic acid ring planes is only 1.22 (7)0with an interplanar spacing between C10...C12 (3.383 (16) Å) and C13...C15 (3.351 (14) Å ). Water influences proton transfer in the hydrogen bonded charge transfer complex, and contributes to generating increased number of hydrogen bonds utilized in the stabilzaation of the crystal structure of the complex. Water serves as an efficient bridge between the chloranilic acid molecules through O-H...O intermolecular hydrogen bonds to form a zigzag channel, as well as directly linking chloranilic acid molecules with benzimidazole molecules which are strongly entrapped within the zigzag channel by intermolecular hydrogen bonding network involving the N-H...O, C-H...O, and C-H...Cl interactions. In the chloranilate anion structure, an intramolecular hydrogen bonding involving O2-H7 and O1 (dO2... O1 and dH7... O1 = 2.670 (12) and 2.25 Å) occurs. The supramolecular architecture of the hydrogen bonded charge complex exhibits a three-dimensional hydrogen bonding network

Synthesis, spectral, structural analysis and biological evaluation of a new hydrogen-bonded charge-transfer complex: 2,3-Dimethylquinoxalinium-p-toluenesulfonate

Studies concentration on hydrogen-bonded charge-transfer complex formed on the reaction between basic 2,3-dimethylquinoxaline with p-toluenesulfonic acid. The crystal was characterized by IR, NMR, thermal and elemental analysis. The crystal structure was deduced by single crystal X-ray diffraction studies which indicated that cation and anion are linked through strong N+—H---O− type of hydrogen bond. The hydrogen bonded charge transfer crystal was screened for its pharmacology, such as Calf thymus DNA binding/cleavage, antioxidant properties. The results indicated that the compound could interact with DNA through intercalation and should have weak to moderate capacity of scavenging with DPPH. The high thermal stability is due to the molecular frame work through H-bonding interaction. The microbial activities of synthesised compound were examined against various bacteria and fungi species.

Design of Ferroelectric Organic Molecular Crystals with Ultrahigh Polarization

Inspired by recent successful synthesis of room-temperature ferroelectric supramolecular charge-transfer complexes, i.e., tetrathiafulvalene (TTF)- and pyromellitic diimide (PMDI)-based crystals (Tayi et al. Nature 2012, 488, 485-489), three new ferroelectric two-component organic molecular crystals are designed based on the TTF and PMDI motifs and an extensive polymorph search. To achieve energetically favorable packing structures for the crystals, a newly developed computational approach that combines polymorph predictor with density functional theory (DFT) geometry optimization is employed. Tens of thousands of packing structures for the TTF- and PMDI-based crystals are first generated based on the limited number of asymmetric units in a unit cell as well as limited common symmetry groups for organocarbon crystals. Subsequent filtering of these packing structures by comparing with the reference structures yields dozens of promising crystal structures. Further DFT optimizations allow us to identify several highly stable packing structures that possess the space group of P2₁ as well as high to ultrahigh spontaneous polarizations (23-127 μC/cm(2)) along the crystallographic b axis. These values are either comparable to or much higher than the computed value (25 μC/cm(2)) or measured value (55 μC/cm(2)) for the state-of-the-art organic supramolecular systems. The high polarization arises from the ionic displacement. We further construct surface models to derive the electric-field-switched low-symmetry structures of new TTF- and PMDI-based crystals. By comparing the high-symmetry and low-symmetry crystal structures, we find that the ferroelectric polarization of the crystals is very sensitive to atomic positions, and a small molecular displacement may result in relatively high polarizations along the a and c axes, polarity reversal, and/or electronic contribution to polarization. If these newly designed TTF- and PMDI-based crystals with high polarizations are confirmed by experiments, the computer-aided ferroelectric material design on the basis of hydrogen-bonded charge-transfer complexes with flexible electron-donor and acceptor molecules would be proven valuable for expediting the search of room-temperature "displasive-type" ferroelectric organic crystals.

Cooperation of Hydrogen-Bond and Charge-Transfer Interactions in Molecular Complexes in the Solid State

Abstract Our recent studies for the development of conducting charge-transfer complexes with well-defined assembled structures based on the cooperation of hydrogen-bond and charge-transfer interactions are described. We have designed and synthesized hydrogen-bonded charge-transfer complexes based on (1) tetrathiafulvalene derivatives having nucleobases, aminobenzo and imidazole moieties, and (2) tetracyanoquinodimethane radical anion salts with hydrogen-bond-functionalized phenalenyl and protonated oligo(imidazole) cations. The directional and site-selective hydrogen-bonds formed various supramolecular network structures, constructing segregated columns as the conduction path. Furthermore, the high polarity of hydrogen-bonds caused strong donor–acceptor or cation–anion electrostatic interactions modulating the ionicity of component molecules and the electronic structure of conduction columns. Such electronic modulation effects in addition to controlling the molecular arrangement realized the first purely organic molecular metal based on a hydrogen-bonded charge-transfer complex in the p-chloranil complex of an imidazole-functionalized tetrathiafulvalene derivative. The proton-donating/accepting ability of the hydrogen-bonding sites afforded the simultaneous proton- and charge-transfer complexes, demonstrating an important prompt for the realization of cooperative proton–electron-transfer systems.