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Systematic experimental study of the electrical transport and static magnetization reveals a direct and delicate interplay between magnetism and superconductivity in the organic materialκ-(BEDT-TTF)2Cu[N(CN)2]Cl, displayed through the specific temperature-pressure phase diagram, and such new effects for organic solids as the reentrant superconductivity in zero applied magnetic field and high-field-induced interchange between superconductivity and the nonmetallic resistive phase in the high-pressure region.

A metallic Langmuir-Blodgett (LB) film which does not require any secondary treatments obtained by using a charge-transfer complex of bis(ethylenedioxy)tetrathiafulvalene (BO) and decyltetracyanoquinodimethane (C 10 TCNQ) was examined. A strong band in the IR region was observed due to the conduction electron. The average charges of the C 10 TCNQ and BO in the LB film were -1 and +0.4, respectively, determined from the shift of the specific bands. The room-temperature conductivity of the film was 10 S/cm. The temperature dependence of conductivity of the film was well fitted by the formula σ=AT -α exp(-E g /2k B T), which is related to an activation-type conduction within the domain boundaries of a granular-structured film. The temperature dependence of the thermoelectric power clearly shows the metallic nature of the film

Supramolecular ferroelectric cocrystals of phenazine (Phz) with chloranilic acid (H(2)ca), bromanilic acid (H(2)ba), and fluoranilic acid (H(2)fa) have been characterized by the interplay between their structural transformations and solid-state acid-base (proton transfer) reactions. At ambient pressure, the Phz-H(2)ca, Phz-H(2)ba, and their deuterated crystals exhibit incomplete proton displacement, which transforms the neutral molecules into semi-ionic at low temperatures below the Curie point (T(c)(IC)TT(c)(I)). For the cocrystal of the less acidic H(2)fa, the ferroelectric phase is induced only by applying hydrostatic pressure above ~0.6 GPa. According to the combined studies of temperature-dependent dielectric permittivity and synchrotron X-ray diffraction, it was proved that the ferroelectric (FE-I) phase is always accompanied at lower temperatures by successive phase transitions to the lattice modulated phases with incommensurate periodicities (IC phase, T(c)(II)TT(c)(IC)) and with commensurate (2- or 3-fold) periodicities (FE-II or FE-III phase, TT(c)(II)). Whereas the ground-state structures at ambient pressure are different from one another among the Phz-H(2)ca (FE-II form), Phz-H(2)ba (FE-III form), and Phz-H(2)fa (paraelectric form), their systematic changes under pressure depict a universal pressure-temperature phase diagram. The possible origins of structural changes are assigned to the valence instability and the frustrated Coulomb interactions that induce the charge disproportionation (coexisting neutral ionic) states with the staging spatial orders.

Electronic structure of an organic charge-transfer complex, M${}_{2}$P-TCNQF${}_{4}$ (M${}_{2}$P: 5,10-dihydro-5,10-dimethylphenazine; TCNQF${}_{4}$: 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane), was investigated by means of optical reflection spectroscopy and x-ray structural analyses. This is an ionic compound and has a unique quasi-two-dimensional (2D) crystal structure in which donor ($D$) molecules of M${}_{2}$P and acceptor ($A$) molecules of TCNQF${}_{4}$ stack respectively along the [100] direction, and $D$ and $A$ molecules also stack alternately along the [111] direction. We evaluated the transfer energy $t$($AA$) between the neighboring $A$ molecules, $t$($DD$) between the neighboring $D$ molecules along the [100] direction, and $t$($DA$) between the neighboring $D$ and $A$ molecules along the [111] direction to be 43 meV, 29 meV, and 67 meV at room temperature, respectively. This demonstrates that an anisotropic 2D electronic structure is formed. By comparing the spectra of the imaginary part of the dielectric constant ${\ensuremath{\varepsilon}}_{2}$ obtained from the polarized reflectivity spectra with the absorption spectrum of K-TCNQF${}_{4}$ and the ${\ensuremath{\varepsilon}}_{2}$ spectra of M${}_{2}$P-PF${}_{6}$, which are composed of 1D $A$ stacks and $D$ stacks, respectively, it was revealed that in M${}_{2}$P-TCNQF${}_{4}$ the optical gap corresponds to the Mott gap transition from ${A}^{\ensuremath{-}}$ to ${A}^{\ensuremath{-}}$, and the ${D}^{+}$ to ${D}^{+}$ transition and the ${A}^{\ensuremath{-}}$ to ${D}^{+}$ transition or equivalently the charge-transfer (CT) transition located at the higher energies. Below the structural and magnetic phase transition temperature ${T}_{c}$ \ensuremath{\sim} 122 K, spin-singlet states are formed via displacements of both $D$ and $A$ molecules. The pattern of molecular displacements was found to be very unique, indicating that the phase transition cannot be attributed to a spin-Peierls-like mechanism. The nature of the phase transition is discussed from the temperature dependences of molecular displacements as well as of the Mott-gap transition and the CT transition.

Although ferroelectric compounds containing hydrogen bonds were among the first to be discovered, organic ferroelectrics are relatively rare. The discovery of high polarization at room temperature in croconic acid [Nature \textbf{463}, 789 (2010)] has led to a renewed interest in organic ferroelectrics. We present an ab-initio study of two ferroelectric organic molecular crystals, 1-cyclobutene-1,2-dicarboxylic acid (CBDC) and 2-phenylmalondialdehyde (PhMDA). By using a distortion-mode analysis we shed light on the microscopic mechanisms contributing to the polarization, which we find to be as large as 14.3 and 7.0\,$\mu$C/cm$^{2}$ for CBDC and PhMDA respectively. These results suggest that it may be fruitful to search among known but poorly characterized organic compounds for organic ferroelectrics with enhanced polar properties suitable for device applications., Comment: Submitted

Introduction Developing organic ferroelectrics with advantages of light-weight, flexible, low-cost, and environmentally benign characteristics is in increasing demand, yet needs elaborate chemical designs of objective functions. Recently, the croconic acid has been found to exhibit high polarization [1], and is the first single-component ferroelectric that is based on the cooperative proton tautomerism. In this study, by the direct observations of the electric polarization field hysteresis on the molecular crystals with β-diketone enol or carboxylic unit, bistability of the hydrogen-bonding chains has been proved to functionalize the ferroelectricity of high polarization performance at room temperature [2].

Application of a high magnetic field to the pressure-stabilized superconducting state appearing below T c1 in κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Cl enhances/induces a resistive ground state below T c2 (< T c1 ). The resistivity in the field-induced phase is insensitive to temperature variation. The field-induced transition is also characterized by a marked resistivity versus field hysteresis and by a pronounced long-time dependence.

Electrical resistivity and magnetization measurements reveal that κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Cl exhibits reentrant superconductivity (reported here for the first time for an organic solid) in a wide pressure region. The behavior based on the subtle balance between superconductivity and resistive (magnetic) phase is affected dramatically by thermal history. The low temperature state below 300 bar is of inhomogeneous mixture of superconductive and non-metallic phases, while the phase in higher pressure region can be single: rich variety of phase are found in pressure phase diagram.

The LB films of the charge transfer complexes of oxygen-containing BEDT-TTF type donor bisethylenedioxytetrathiafulvalene (BO) and long-chain derivatives of tetracyanoquinodimethane (C n TCNQ) are prepared with and without matrix molecules. The measurements of π-A isotherm for the complex-icosanoic acid mixed system indicated the formation of mixed monolayers at the air-water interface. This was confirmed by the AFM measurements showing a granular structure of the film with the grain size of 100 nm in diameter and 3–4 nm in height. These grains are probably attributable to the BO complex. The conductivity of the LB films were strongly affected by the film-deposition method, the spreading solvent and the matrix. The mixed LB films of BO-C 10 TCNQ and BO-C 14 TCNQ with icosanoic acid under suitable conditions showed conductivities as high as 10 and 3 S/cm, respectively. The former LB film showed a metallic temperature dependence of conductivity down to 250 K. The conduction mechanism is discussed in terms of the film granuality.

The resistivity decrease in α-(BEDT-TTF)2KHg(SCN)4 appearing in the temperature region below 300 mK was found to be suppressed by a magnetic fields of less than 0.1 T. We argue that the decrease in resistivity is due to the superconductivity occurring in a fibril-like structure. The observed behavior is in part due to the inhomogeneous molecular arrangement, but is also related to the subtle interplay between magnetism and superconductivity in this system.

Combining BEDO-TTF with 24 kinds of organic acceptors, 19 kinds of metallic complexes were obtained. The first redox potentials of the the acceptors which give the metallic complexes range over 0.82 V that is anomalously big among the organic metals of conventional 1:1 TTF-TCNQ system. The crystal structure of the (BEDO-TTF) 5 (HCTMM)(PhCN) 2 salt is regarded as one of the self-aggregated packing motif of the partially charged BEDO-TTF in which the donor interacts to each other through the side-by-side heteroatom network and through the face-to-face stacking. The semiconducting (BEDO-TTF) 5 (HCP)(PhCN) 0.2 salt preserves the common structural features to the metallic BEDO-TTF salts. The strong tendency of BEDO-TTF to produce organic metals is attributed both to its low ionization energy and to the ability of its self-aggregation.

BEDO-TTF which is one of the oxygen substituted BEDT-TTF analogues, gave conductive organic charge transfer complexes in contrast to BEDT-TTF and other BEDT-TTF derivatives. Especially many complexes exhibit metallic temperature dependences even with the compressed disks. These facts suggest the remarkable tendency of BEDO-TTF to aggregate themselves.

The role of solitons in transport, dielectric, and magnetic properties has been revealed for the quasi-one-dimensional organic charge-transfer salt, $\mathrm{TTF}\mathrm{\text{\ensuremath{-}}}{\mathrm{QBrCl}}_{3}$ [tetrathiafulvalene (TTF)-2-bromo-3,5,6-trichloro-$p$-benzoquinone (${\mathrm{QBrCl}}_{3}$)]. The material was found to be ferroelectric and hence the solitons should be located at the boundary of the segments with opposite electric polarization. This feature enabled the electric-field control of soliton density and hence the clear-cut detection of soliton contributions. The gigantic dielectric response in the ferroelectric phase is ascribed to the dynamical bound and creeping motions of spinless solitons.

BEDO-TTF which is one of the oxygen substituted BEDT-TTF analogues, gave conductive organic charge transfer complexes in contrast to BEDT-TTF and other BEDT-TTF derivatives. Especially many complexes exhibit metallic temperature dependences even with the compressed disks. These facts suggest the remarkable tendency of BEDO-TTF to aggregate themselves.

We have investigated the polarization $\ensuremath{\pi}$-molecular skeleton coupled dynamics for the proton-displacive organic ferroelectrics, cocrystal of phenazine with the 2,5-dihalo-3,6-dihydroxy-p-benzoquinones by measurements of the terahertz/infrared spectroscopy. In the course of the ferroelectric-to-paraelectric transition, the ferroelectric soft phonon mode originating from the intermolecular dynamical displacement is observed in the imaginary part of dielectric spectra ${ϵ}_{2}$, when the electric field of the light $(E)$ is parallel to the spontaneous polarization $(P)$. The soft phonon mode is isolated from the intramolecular vibrational mode and hence the intramolecular skeleton dynamics is almost decoupled from the polarization fluctuation. In the spectra for $E$ parallel to the hydrogen-bonded supramolecular chain, by contrast, the vibrational mode mainly originating from the oxygen atom motion within the $\ensuremath{\pi}$-molecular plane is anomalously blurred and amalgamated into the polarization relaxation mode concomitantly with the dynamical proton disorder. This indicates that the dynamical disorder of the intramolecular skeleton structure, specifically that of oxygen atom, is strongly enhanced by the proton fluctuation and is significantly coupled to the polarization fluctuation along the hydrogen-bonded supramolecular chain. The results are discussed in terms of the proton-mediated anisotropic polarization $\ensuremath{\pi}$-molecular skeleton interaction, which characterizes these emerging proton-displacive ferroelectrics.

We have investigated the optical response resulting from the proton-$\ensuremath{\pi}$-electron-molecular-skeleton coupled dynamics in an organic ferroelectric 55DMBP-Hia. Upon the ferroelectric-to-paraelectric transition, almost all of the vibrational modes below $500\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}1}$ are anomalously blurred and amalgamated into the high-frequency tail of the polarization-relaxation mode. This indicates that the constituent molecular shape is no more well defined around ${T}_{C}$ due to the dynamical disorder of the $\ensuremath{\pi}$-conjugated structure originating from proton delocalization on the intermolecular bifurcated hydrogen bond.

Organic ferroelectrics are multifunctional candidates for future organic electronic and optical devices. In spite of their potential, only a few organic compounds are known to exhibit a ferroelectric transition. The conventional approach to ferroelectrics, in general, relies on the use of asymmetric dipolar molecules and/or substituents. Recently, distinct design strategies have been developed using the molecular compounds of binary- or multi-components, combined with “non-covalent” forces: charge-transfer interactions and/or hydrogen bonding. This article focuses on the supramolecular systems of hydrogen-bonded acid and base molecules. Ferroelectricity and a significant dielectric response, as well as an antiferroelectric ordering induced by proton transfer, are demonstrated in the hydrogen-bonded chains composed of 2,5-dihydroxy-p-benzoquinone derivatives and nitrogen-containing aromatic bases.

A 1:1 adduct of phenazine (Phz) with chloranilic acid (H2ca) and bromanilic acid (H2ba), in which nonpolar neutral molecules are connected by the intermolecular O−H···N hydrogen bonds, shows ferroelectric transitions. Neutron diffraction analysis of these materials reveals that there are two inequivalent hydrogen-bonding sites below the ferroelectric transition temperature (253 K for Phz-H2ca and 168 K for Phz-H2ba). This asymmetry was also observed by the maximum entropy method (MEM) analysis of the synchrotron X-ray diffractions. The structure analysis results suggest that the origin of the polarization of the material is the symmetry breaking based on the two inequivalent hydrogen bonds.

A 1:1 adduct of chloranilic acid with 5,5'-dimethyl-2,2'-bipyridine, in which two kinds of molecules are connected by infinite hydrogen bond chains, exhibits a distinct dielectric phase transition when cooled. Below T(c)(=318 K) the hydrogen atoms participating in hydrogen bonding undergo long-range ordering and form an antiferroelectric-like state, taking a single minimum potential in the high-temperature phase (TT(c)) due to the bifurcate hydrogen bond system. The proton-transfer phenomenon was clearly observed by electron density distribution analysis using a maximum entropy method of synchrotron x-ray diffraction data.

Ferroelectricity and large dielectric constant at room temperature have been demonstrated for cocrystals of phenazine and anilic acids constructing supramolecular assemblies. Deuteration of the anilic acids gives rise to an increase by more than 50 K in the transition temperature, which exceeds room temperature for the deuterated chloranilic acid. At room temperature in air, the crystals show a clear polarization hysteresis with a small coercive field. Application of hydrostatic pressure and halogen substitution in the anilic acids bring about the structural effect on the transition temperature in a parallel way, whereas the deuterium substitution does this in a distinct way. The observed large deuteration effect cannot be elucidated by the geometric change of the hydrogen bond, which has been considered as the possible mechanism of ferroelectricity in the conventional hydrogen-bonded with double-well potential.

A stripe pattern with a spacing of a few micrometers is observed to show up on the crystal surface of a potassium 7,7',8,8'-tetracyanoquinodimethane (K-TCNQ) upon the current-induced local insulator-metal transition. The spatially resolved reflectivity and Raman spectroscopies have shown that the stripe is a consequence of periodic phase separation with alternate dimerized and less-dimerized domains in the TCNQ stacks. The periodic modulation of the electronic state is generated in order to minimize the energy of the lattice strain, arising from the current-induced relaxation of the Peierls distortion.

The Hall effect of a metallic Langmuir–Blodgett film based on bisethylenedioxytetrathiafulvalene complex of decyltetracyanoquinodimethane has been investigated using a double ac Hall method. The polarity of the Hall coefficient is positive over the measuring temperature range. The carrier density is of the order of 1021 cm−3, almost independent of temperature, and the Hall mobility, of around 0.05 cm2 (V s)−1 at room temperature, is in a single activated process. The Hall results have been interpreted with an inhomogeneous structure model, and support that metallic domains are developed throughout the whole sample.

Supramolecular ferroelectric cocrystal of phenazine (Phz) with chloranilic acid (H2ca), which exhibits three successive phase transitions, have been characterized by the interplay between their structural transformations and solid-state acid–base (proton transfer) reactions (Figure) [1]. This material undergoes a ferroelectric phase (FE-I phase) transition of displacive-type at 253 K followed by successive phase transitions to the lattice modulated phases with incommensurate periodicities and with commensurate 2-fold periodicity (FE-II phase) at lower temperature [2]. To elucidate the origin of the ferroelectricity in the FE-I phase, it is crucial to study the crystal structure using single crystals. The synchrotron x-ray diffraction experiment was carried out on the imaging-plate diffractometer at BL-8A of Photon Factory in KEK. Superstructure reflections with the modulation wave vector q=(1/2 1/2 1/2) were clearly observed below 103 K. Considering the preserved 2/m Laue symmetry, the lattice can be transformed to a C-centered monoclinic lattice, which is related by (-2a, -2b, a + c) or (2a, -2b, -a - c) with the FE-I structure. Although the lattice distortion and the intensities of the superlattice reflections are consistent with the 2/m Laue symmetry, the space group C1 is deduced from the polar nature and a subgroup symmetry of the FE-I structure. Moreover, we performed single-crystal neutron diffraction experiments at SENJU of MLF/J-PARC in order to determine the displacement of the hydrogen atom. The crystal structure analysis at 10 K was carried out using the reflections measured in a half-sphere of reciprocal space at d > 0.4. The structure analysis was performed on the basis of the space group C1, where four Phz and four H2ca become crystallographically inequivalent. Finally, all the structural parameters including all hydrogen atoms were successfully refined. In the FE-II phase, the neutral and ionic molecules alternately align along the π-molecular stack.

Using a terahertz-radiation imaging, visualizations of ferroelectric domains were made in a room-temperature organic ferroelectric, croconic acid. In as-grown crystals, observed are ferroelectric domains with sizes larger than 50-μm square, which are separated by both 180° and tail-to-tail domain walls (DWs). By applying an electric field along c axis (the polarization direction), a pair of 180° DWs is generated and an each 180° DW oppositely propagates along a axis, resulting in a single domain. By cyclic applications of electric fields, a pair of 180° DWs repeatedly emerges, while no tail-to-tail DWs appear. We discuss the usefulness of the terahertz-radiation imaging as well as the observed unique DW dynamics.

Linear and nonlinear optical responses in a molecular crystal, croconic acid, showing electronic-type ferroelectricity were studied by reflection and second harmonic generation spectroscopy. The second-order nonlinear susceptibility χ(2) was very large, exceeding 10−6 esu in the near-infrared region. The enhancement of χ(2) was attributed to the large dipole moment of the lowest π–π* transition and the large difference between the molecular dipole moments for the ground state and the photoexcited state. We deduced the molecular orbitals (MOs) and dipole moments responsible for the large χ(2) by comparing the experimental optical parameters and MO calculation results based upon density functional theory.

The first in situ electrical conductivity measurement of monolayers on water during compression on a Langmuir-Blodgett trough are reported for bis(ethylenedioxy)tetrathiafulvalene Ivalene and 2-decyl-7,7,8,8-tetracyanoquinodimethane systems, the conductivity of the monolayers being ca. 0.6 S cm-1.

Ferroelectricity has been time-honored subject in terms of various electronic, electro-mechanical, and optical functions. Developing organic ferroelectrics with advantages of light-weight, flexible, low-cost, and environmentally benign characteristics is surely in demand, yet needs elaborate chemical designs of objective functions. This review describes modern chemical approach to improved dielectric, ferroelectric and/or thermal properties, based on the charge-transfer complexes and hydrogen-bonded compounds.

Raman spectroscopy was applied as an accurate general method for determination of the charge on BO (ρ). Two C=C stretching modes of BO, (a g ) ν 2 and ν 3 , linearly correlate with p in the region 0 ≤ ρ ≤2. Features of BO complexes with organic acceptors are discussed.

The electronic structure of organic ferroelectric tetrathiafulvalene– p -bromanil (TTF–BA) have been studied by first-principles calculations. It has been found that two antiferromagnetic ordered s...

79 Br NQR measurement is performed to determine the low-energy charge-transfer/dimerization fluctuations in the organic charge-transfer complex DMTTF–2,6-QBr 2 Cl 2 . With decreasing temperature, NQR line width gradually increases and the spin–lattice relaxation rate 1/ T 1 shows a large enhancement from the two-phonon relaxation law ( T 7 ). This behavior is consistent with the picture that the present material is situated in the critical region of the charge-lattice-coupled quantum transition.

Hydrogen bonding in solids has provided diverse attractive issues. Prof. C. N. R. Rao and his collaborators have made representative achievements on experimental and theoretical grounds as well as on the resultant crystal engineering and functionalities. Many of the key issues clarified in those extensive studies are valid in our investigations on ferroelectricity of hydrogen-bonded supramolecules, linear chain cocrystals of phenazine (Phz) with anilic acids (H2xa). Ferroelectrics have a spontaneous polarization that is switchable by an applied electric field, and have long constituted numerous technological applications such as capacitors, sensors, and information storage devices. In this paper, we overview the dielectric, ferroelectric, structural, and optical properties of such a family of hydrogen-bonded cocrystals as complemented with some latest advances to disclose the key experimental findings. Excellent ferroelectric properties are highlighted by the large response under small electric field in spite of the use of originally neutral and nonpolar constituents. The ferroelectric phase transition asymmetrically elongates an O–H bond with the strengthened O–H⋯N intermolecular bond. This mechanism is distinct from the site-to-site collective transfer of protons observed in conventional ferroelectrics like KH2PO4 (KDP). Rather, it represents quite an exotic proton displacement, being an incipient phenomenon of the transition from the neutral to the monovalent ionic form. Furthermore, the lower temperature regions find successive phase transitions to an additional ferroelectric phase having a doubled or threefold supercell. Periodic proton ordering is proposed as a possible picture of this ground state.

The effect of molecular substitution on the neutral-ionic (NI) phase transition has been investigated for TTF-p-chloranil (QCl4) by the measurements of dielectric constant. Due to the ferroelectric nature in the transformed ionic state, the dielectric constant shows a large anomaly at the NI transition temperature, which was remarkably but continuously lowered down to zero temperature by the molecular substitution. X-ray structural analysis revealed the large “chemical pressure” effect for TSF doped crystals.

The π-electronic functionalities of molecular donor ( D )–acceptor ( A ) compounds have been attracting subjects for the solid state science as well as for the prospective technological exploitation in organic electronics. In this review, it is shown that the novel neutral–ionic valence instability in the charge-transfer (CT) complexes is closely related to valuable electric properties such as the current-induced resistance switching, quantum phase transition, gigantic dielectric response, and relaxor ferroelectricity. Furthermore, the displacive-type ferroelectricity has recently been developed on the D A combinations in the hydrogen-bonded co-crystals. It is also discussed that the intermolecular CT mechanism in the molecular D A compounds is promising to advance the potential of organic field-effect transistors (FETs) that are envisioned as key components in future organic electronics.

A stable, highly conductive Langmuir-Blodgett (LB) film was developed with a charge-transfer (CT) complex of bisethylenedioxytetrathiaful valene (BO) and dimethoxytetracyanoquinodimethane using the unique nature of BO molecules. The metallic temperature dependence of electrical conductivity was observed down to 180 K, showing a maximum of 13 S/cm. The X-ray diffraction measurements show the presence of three kinds of domains corresponding to CT complex, icosanoic acid and disordered CT complex regions. The behavior of macroscopic electrical conductivity is understood well by a percolation model consisting of metallic, semiconducting and insulating sites.

New surface conductive polymer composite films exhibiting extraordinary properties: high conductivity with metallic temperature dependence and exceptionally high transparency are presented. The conducting networks in these materials are formed of plate-like nanocrystals of bis(ethylenedioxy)tetrathiafulvalene (BEDO-TTF) salts with iodine or bromine. The films with bromine salts are colorless and transparent while those with iodine are colored. It is demonstrated that colored films with (BEDO-TTF)/iodine networks can be electrochemically transformed into highly transparent, practically colorless materials without deterioration of the conducting network. The resulting metallically conducting polymer materials show the highest transparency among conductive composites reported so far.

The charge transfer properties of alkylTCNQ derivatives in the LB films of molecular conductors were examined. TMTTF, OMTTF and BEDOTTF were adopted as donors to form charge transfer complexes with C10 TCNQ or C14TCNQ. The degree of charge transfer of the alkylTCNQ in the LB films could be controlled from nearly neutral to fully ionic state by adopting appropriate donors for the counterpart. OMTTF-C10TCNQ formed a neutral complex which is located near the neutral-ionic boundary and is expected to be a candidate to realise neutral-ionic phase transition in the LB films.

Preparation, characterization, and physical properties of several metallic bis(ethylenedioxy)tetrathiafulvalene (BEDO-TTF) complexes are presented. The direct reaction with chloranilic acid (H2CHA) gave 2:1 complex, the crystal structure of which consists of two-dimensional (2D) donor layer and 1D stack of deprotonated acceptor molecules. The electrocrystallization of the donor in the presence of MnBr42− and water yielded a novel salt with four components, (BEDO-TTF)2Br[MnBr2(H2O)4](H2O), which contains 2D donor layers and localized magnetic moments ( S = 5 2 ).

We report the results of resistivity measurements carried out on single crystals of κ-(ET)2Cu-[N(CN)2]Cl in an applied magnetic fields to 10 T. Hydrostatic pressures have been used to stabilize the metallic state and superconductivity. In a fields to 10 T applied parallel to the highly conducting a-c plane, and in a low fields normal to the plane the field effect on the superconducting transition is observed to be similar to other layered superconductors. However, the application of a higher fields normal to the a-c plane causes the resistivity to exhibit sharp metal/superconductor to insulator transition.

We report on resistivity measurements under hydrostatic gas pressure and ambient pressure dc magnetization which reveal that in a layered organic compound κ-(ET) 2 Cu[N(CN) 2 ]Cl an insulating magnetic phase and superconductivity coexist in a wide pressure region P ≥ 1 bar, and their interplay causes the reentrant superconductivity in zero applied magnetic field.

Infrared optical spectra have been investigated for a charge-transfer complex of tetrathiafulvalene and 2-bromo-3,5,6-trichloro- $p$-benzoquinone, which undergoes a neutral-ionic ( $N\ensuremath{-}I$) transition at ${T}_{c}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}68\mathrm{K}$. With the decrease of temperature toward ${T}_{c}$, the far-infrared reflectivity spectrum is gradually transformed into a Drude-like high reflectance band edging around $100{\mathrm{cm}}^{\ensuremath{-}1}$, and the optical conductivity shows an anomalous peak around $10{\mathrm{cm}}^{\ensuremath{-}1}$. The far-infrared anomaly is related to the gigantic dielectric response just above ${T}_{c}$, which are both discussed in terms of dynamics of $N\ensuremath{-}I$ domain walls with fractional charge.