Biased Bowl-Direction of Monofluorosumanene in the Solid State.

A new curved π-conjugated molecule 1-fluorosumanene (1) was designed and synthesized that possesses one fluorine atom on the benzylic carbon of sumanene. This compound can exhibit bowl inversion in solution, leading to the formation of two diastereomers, 1endo and 1exo, with different dipole moments. Experimental and theoretical investigation revealed an energetical relationship among 1exo, 1endo, and solvent to realize the various endo:exo ratios in the single crystals of 1 depending on the crystallization solvent. Significantly, the molecular dynamics (MD) simulations revealed that 1exo positively worked for the elongation of the stacking structure and the final endo:exo ratio was affected by the relative stability difference between 1endo and 1exo derived by solvation. Such an arrangeable endo:exo ratio of 1 realized the preparation of unique materials showing a different dielectric response from the same molecule 1 just by changing the crystallization solvent.

Carrier Transport Switching of Ferroelectric BTBT Derivative.

Alkylamide-substituted [1]benzothieno[3,2-b][1]benzothiophene (BTBT) derivative of BTBT-NHCOC14H29 (1), which has ferroelectric N-H···O= hydrogen-bonding network of alkylamide group and two-dimensional (2D) electric structure of BTBT π-cores, was prepared to design the external electric field-responsive organic semiconductors. The short-chain derivative of BTBT-NHCOC3H7 (1') revealed the coexistence of a 2D electronic band structure based on the herringbone BTBT arrangement and the one-dimensional (1D) hydrogen-bonding chain. 1 formed a smectic E (SmE) liquid crystal phase above 412 K and showed ferroelectric hysteresis in the electric field-polarization (P-E) curves at 403-433 K. The remanent polarization (Pr) and coercive electric field (Ec) of 1 at 408 K, 0.1 Hz were 24.0 µC cm-2 and 5.54 V µm-1, respectively. By thermal annealing of thin-film 1 at 443 K, the molecular assembly structure of 1 changed from a monolayer to a bilayer structure with high crystallinity, resulting in conducting layers of BTBT parallel to the substrate surface. The organic field-effect transistor (OFET) device with thermally annealed thin-film 1 showed p-type semiconducting behavior with the hole mobility of 1.0 × 10-3 cm2 V-1 s-1. Furthermore, device 1 showed switching behavior of semiconducting properties by electric field poling and thermal annealing cycle. The electric field response of ferroelectrics modulated the molecular orientation and conduction properties of organic semiconductors, resulting in external electric field control of carrier transport properties.

Endocytosis-Like Vesicle Fission Mediated by a Membrane-Expanding Molecular Machine Enables Virus Encapsulation for In Vivo Delivery.

Biological membranes are functionalized by membrane-associated protein machinery. Membrane-associated transport processes, such as endocytosis, represent a fundamental and universal function mediated by membrane-deforming protein machines, by which small biomolecules and even micrometer-size substances can be transported via encapsulation into membrane vesicles. Although synthetic molecules that induce dynamic membrane deformation have been reported, a molecular approach enabling membrane transport in which membrane deformation is coupled with substance binding and transport remains critically lacking. Here, we developed an amphiphilic molecular machine containing a photoresponsive diazocine core (AzoMEx) that localizes in a phospholipid membrane. Upon photoirradiation, AzoMEx expands the liposomal membrane to bias vesicles toward outside-in fission in the membrane deformation process. Cargo components, including micrometer-size M13 bacteriophages that interact with AzoMEx, are efficiently incorporated into the vesicles through the outside-in fission. Encapsulated M13 bacteriophages are transiently protected from the external environment and therefore retain biological activity during distribution throughout the body via the blood following administration. This research developed a molecular approach using synthetic molecular machinery for membrane functionalization to transport micrometer-size substances and objects via vesicle encapsulation. The molecular design demonstrated in this study to expand the membrane for deformation and binding to a cargo component can lead to the development of drug delivery materials and chemical tools for controlling cellular activities.

Noninvasive Three-dimensional Assessment of Single Molecular Crystals Using Multiphoton Microscopic Observation and Their Deformation-induced Emission Characteristics.

Distinguishing the luminescence contribution from the surface and bulk of a crystal is a long-standing challenge in crystal materials. Herein, three-dimensional, multiphoton, luminescence microscope imaging of the elastic molecular single crystal 1,4-bis(4-methylthien-2-yl)-2,3,5,6-tetrafluorobenzene, was conducted. Further, the luminescence contribution from the surface and bulk of the crystal was experimentally distinguished. Strong luminescence was observed only from the surface of the crystal, while the bulk did not emit strongly. Furthermore, the surface and bulk luminescence behavior responded well to the mechanical shape change of the crystal; i.e., strong luminescence was observed for the elongated side of the crystal.

Selective Gas Sensing under a Mixed Gas Flow with a One-Dimensional Copper Coordination Polymer.

Structural changes of the coordination polymer associated with gas adsorption (gate opening-type adsorption) can be linked to bulk physical properties such as magnetism, electrical conductivity, and dielectric properties. To enable real-space sensing applications, it is imperative to have a system where the selective adsorption of mixed gases can be correlated with physical properties. In this report, we demonstrate that a crystalline sample of one-dimensional (1D) coordination polymer exhibits selective CO2 adsorption while simultaneously displaying dielectric switching behavior in a mixed N2/CO2 gas environment. In the crystal of {[Cu2(2-TPA)4(pz)]·CH3CN}n (1·CH3CN), where 2-TPA and pz are 2-thiophencarboxylate and pyrazine, respectively, paddle wheel-type units of [Cu2(2-TPA)4] are bridged by pz, forming a 1D chain structure. One of the two crystallographically independent 2-TPA units was interacted with the pz moiety of the adjacent 1D chain by π···π interactions, forming a two-dimensional (2D) layer parallel to the ab plane. Activated 1 shows selective CO2 adsorption by a gate opening-type adsorption mechanism, indicating that the CO2 adsorption process is accompanied by a structural change. The change in the real part of dielectric permittivity (ε') under the mixed N2/CO2 gas flow is a result of the selective CO2 adsorption, which was supported by the enthalpy changes (ΔH) associated with CO2 adsorption in two methods: CO2 adsorption isotherms and temperature-dependent measurements of ε' under a mixed N2/CO2 gas flow. The calculated ΔH values were found to be in good agreement across both methods. The CO2 ratio in the mixed N2/CO2 gas flow increased, and the switching ratio of ε' (Δε') also increased. Notably, Δε' exhibited a marked increase beyond the pressure required for gate opening adsorption.

Proton Conduction at High Temperature in High-Symmetry Hydrogen-Bonded Molecular Crystals of RuIII Complexes with Six Imidazole-Imidazolate Ligands.

A new H-bonded crystal [RuIII (Him)3 (Im)3 ] with three imidazole (Him) and three imidazolate (Im- ) groups was prepared to obtain a higher-temperature proton conductor than a Nafion membrane with water driving. The crystal is constructed by complementary N-H⋅⋅⋅N H-bonds between the RuIII complexes and has a rare Icy-c* cubic network topology with a twofold interpenetration without crystal anisotropy. The crystals show a proton conductivity of 3.08×10-5  S cm-1 at 450 K and a faster conductivity than those formed by only HIms. The high proton conductivity is attributed to not only molecular rotations and hopping motions of HIm frameworks that are activated at ∼113 K, but also isotropic whole-molecule rotation of [RuIII (Him)3 (Im)3 ] at temperatures greater than 420 K. The latter rotation was confirmed by solid-state 2 H NMR spectroscopy; probable proton conduction routes were predicted and theoretically considered.

Proton Conduction at High Temperature in High-Symmetry Hydrogen-Bonded Molecular Crystals of RuIII Complexes with Six Imidazole-Imidazolate Ligands.

Invited for the cover of this issue is mainly the group of Makoto Tadokoro and co-workers at Tokyo University of Science. Other co-workers are Masaki Itoh, Ryota Nishimura, Kensuke Sekiguchi (TUS students), Dr. Norihisa Hoshino (Tohoku Univ.), Dr. Hajime Kamebuchi (Nihon Univ.), Dr. Jun Miyazaki (Tokyo Denki Univ.), Prof. Motohiro Mizuno (Kanazawa Univ.) and Prof. Tomoyuki Akutagawa (Tohoku Univ.). The image depicts on two mechanisms of proton transport rotations of the proton-conductive starburst molecule [RuIII (HIm)3 (Im)3 ]. Read the full text of the article at 10.1002/chem.202201397.

Benzenetriimide-Based Molecular Conductor with Antiferro- to Ferromagnetic Switching Induced by Structural Change of π-stacked Array.

Benzenetriimide (BTI) is a promising building block for materials chemistry due to its characteristic 3-fold symmetry and redox properties, whereas little is known about its conductive and magnetic properties. In this study, we synthesized three charge-transfer complexes based on N,N',N''-trimethylbenzenetriimide (BTI-Me). One of the complexes contains isolated dimers of BTI-Me radical anion (BTI-Me⋅- ), while the other two have the infinite π-stacked array of BTI-Me with the formal charge of -0.5. The latter two complexes did not show metallic behavior but showed semiconducting behavior probably due to the characteristic insulation in one-dimensional electron system, so-called charge ordering and dimer-Mott insulation. The magnetic susceptibility of the complex in dimer-Mott state exhibits an unusual transition from antiferromagnetic to ferromagnetic spin states with the hysteresis loop of 15 K derived from the structural phase transition around 130 K. These properties were also supported by DFT calculations.

Crystal Lattice Design of H2O-Tolerant n-Type Semiconducting Dianionic Naphthalenediimide Derivatives.

Dianionic bis(propionate)-naphthalenediimide (PCNDI2-) formed simple 2:1 cation-anion salts of (M+)2(PCNDI2-)·(H2O)n (M+ = Li+, Na+, K+, Rb+, and Cs+), which exhibited reversible H2O adsorption-desorption behavior because of the presence of their electrostatically binding crystal lattices. The maximum H2O adsorption amounts (n) for M+ = Li+, Na+, K+, Rb+, and Cs+ were 0.25, 6.0, 4.0, 6.0, and 2.0, respectively, whereas the reversible gate-opening (gate-closing) H2O adsorption-desorption isotherms were observed at 273 and 298 K, except for M+ = Li+. High ionic conductivities of around 10-4-10-5 S cm-1 were observed in M+ = Na+ and K+ salts, whereas short-range thermal fluctuations occurred in large cations of M+ = Rb+ and Cs+. The change in the electrostatic lattice energy for M+ = Na+ and K+ salts during the H2O adsorption-desorption cycles was significantly larger than those for M+ = Rb+ and Cs+. Therefore, the Na+ and K+ salts had a considerably flexible electrostatic crystal lattice with a large amplitude of lattice modulation during the H2O sorption cycle. In contrast, the lattice modulation for M+ = Rb+ and Cs+ salts involved a low magnitude of ion displacements, forming a relatively rigid cation-anion electrostatic crystal lattice. The flash-photolysis time-resolved microwave conductivity and transition absorption spectroscopy results revealed the high electron mobility of H2O-adsorbed thin films, wherein the crystallized H2O molecules did not act as electron-trapping sites. The values of electron mobility increased in the order of Cs+ ≈ Rb+ > K+ > Na+ > Li+.

Inversion Symmetry Breaking in Order-Disorder Transitions of Globular Ligands Coordinating to Cobalt(II) and Nickel(II) Bisacetylacetonato Complexes During Heating.

Unexpected inversion-symmetry breaking was observed in the order-disorder phase transitions of [M(acac)2 (abco)2 ] (1; M=Co2+ , 2; Ni2+ , acac- =2,4-pentanedionato, abco=1-azabicyclo-[2.2.2]-octane=quinuclidine) during heating. The isostructural, transition-free complexes [M(acac)2 (cabco)2 ] (3; M=Co2+ , 4; Ni2+ , cabco=3-chloro-1-azabicyclo-[2.2.2]-octane=3-chloroquinuclidine) were also studied for comparison. Complexes 1 and 2 crystallized in ordered phases in the centrosymmetric I2/m space group at 100 K, whereas they crystallized in disordered phases in the non-symmetric I2 space group at 300 K. The 60° step rotation disordering of the abco ligands was observed in the electron density maps of 1 and 2, which was consistent with the transition enthalpies estimated by differential scanning calorimetry (DSC). Gradual phase transitions were observed for 1 and 2 by DSC and powder X-ray diffraction (PXRD) at approximately 225 K. The inversion-symmetry disordering was likely induced by the local pseudo-symmetry of the abco ligands, increasing from trigonal to hexagonal and the increased steric repulsion pathways among them.

Photoinduced Generation of the π-Conjugated Zwitterionic State in the ESIPT Fluorophore of 2,4-Bisimidazolylphenol.

We demonstrate that 2,4-bis(4,5-diphenyl-1H-imidazol-2-yl)phenol (2,4-bImP) undergoes photoinduced conversion into the so-called "π-conjugated zwitterion" after causing an excited-state intramolecular proton transfer (ESIPT) reaction. The powder sample of 2,4-bImP exhibits largely Stokes-shifted fluorescence characteristics to ESIPT fluorophores. On the other hand, its originally colorless solutions become colored when exposed to UV light for several minutes, whose color depends on the type of solvent. In particular, the CHCl3 solution rapidly turns dark green with the absorption maximum around 700 nm, and the colored solution is nearly restored to original by alternating addition of acid and base. To explain such drastic and reversible color changes, we hypothesized that the occurrence of ESIPT (i.e., deprotonation of the phenol and protonation of the imidazolyl group at its 2-position) triggered the charge-separated structure between the negatively charged phenolate and the positively charged imidazoliumyl group at its 4-position, which allowed resonance with the neutral p-quinoid structure. The formation of this π-conjugated zwitterion was strongly supported by the results of 1H and 15N NMR and Raman measurements.

Negative-to-Positive Thermal Conductivity Temperature Coefficient Transition Induced by Dynamic Fluctuations of the Alkyl Chains in the Layered Complex (C4 H9 NH3 )2 CuCl4.

A negative-to-positive transition of the temperature coefficients of thermal conductivity was found in the two-dimensional organic-inorganic layered complex (C4 H9 NH3 )2 CuCl4 (C4CuCl4) over the three structural phase transitions in the range 176-218 K. The coefficients of the low-temperature phases (85-200 K, α and ß phases) were negative, as is typical for insulating crystals, whereas those of the high-temperature phases (200-300 K, γ and δ phases) were positive, as is typical for glasses and liquids. Single-crystal X-ray structure analyses revealed that the tilted C4 H9 NH3 + chains in the α and ß phases were fully outstretched in the δ phase, and the interlayer distances between the CuCl4 2- planes increased significantly. The γ phase was an intermediate phase that crystallized with an incommensurate structure, in which the CuCl4 2- sheets formed wave-like structures consisting of connected alternating regions of ß-like and δ-like moieties. In the γ and δ phases, thermal fluctuations of the C4 H9 NH3 + chains were found in the electron density maps; however, powder X-ray diffraction (PXRD) data indicated that the thermal expansion of the C4 H9 NH3 + layers was restricted by the rigid CuCl4 2- layers. This situation was considered to induce glass-like thermal conducting properties in the material, such as a positive temperature coefficient. The mean free path of the phonons estimated by using the thermal conductivities and heat capacities was a function of T-1 in the range 85-200 K, as would be expected for crystals, whereas it was approximately constant in the range 200-300 K, which is typical of glasses. In addition, the existence of soft vibration modes in the two-dimensional perovskite CuCl4 2- sheets was revealed by analysis of the incommensurate crystal structure of the γ phase. These low-energy vibration modes were believed to induce the cooperative phase transitions, along with the thermal fluctuations and van der Waals interactions in the C4 H9 NH3 + layers.

Interfacial Nanostructuring of Poly(vinylidene fluoride) Homopolymer with Predominant Ferroelectric Phases.

Facile preparation of poly(vinylidene fluoride) (PVDF) homopolymer nanoparticles (NPs) with monodispersed size distribution and predominant ferroelectric phases was done in an interfacial nonsolvent (water/methanol)-solvent (dimethylformamide (DMF))-polymer (PVDF) ternary system using two interfacial nanoassembly methods. First, a fluidic liquid-liquid interface consisting of two miscible solvents was created by introducing nonsolvent (water) under the PVDF solution. After the interface was created, the interface moved up to the DMF phase direction; PVDF NPs were produced through nonsolvent-induced phase separation. As the water content decreased in the nonsolvent by mixing with methanol, PVDF structures changed from nanoparticles with 252 nm average diameter (PVDF NP-1) to a porous membrane through membrane-wrapped NPs. The phenomena were found to be related to the mutual affinity of solvent, nonsolvent, and PVDF. When an additional external force was introduced to the water-DMF-PVDF system through magnetic stirring (reprecipitation method), smaller PVDF NPs with 61.4 nm diameter were obtained (PVDF NP-2). Both the as-prepared PVDF NPs were demonstrated with the predominant ferroelectric (electroactive (EA)) phase up to 97-98% among crystalline phases, which is apparently the highest value ever reported for PVDF homopolymer NPs. It is noteworthy that PVDF NP-2 showed a higher ß phase ratio than that of PVDF NP-1, as proved using Fourier transform infrared (FT-IR) spectroscopy. Also, differential scanning calorimetry (DSC) and X-ray diffraction (XRD) measurements revealed that PVDF NP-1 exhibited higher crystallinity and that PVDF NP-2 underwent a well-separated two-step phase transition under heating. Results suggest that controlling interface formation with DMF and water plays a crucial role in manipulating ferroelectric PVDF nanostructures in terms of crystallinity and the ferroelectric ß phase-to-γ phase ratio.

Titania Nanofilms from Titanium Complex-Containing Polymer Langmuir-Blodgett Films.

This paper proposes a method of fabricating low-dimensional TiO2 nanofilms at room temperature under ambient pressure conditions. The titanium-containing polymer complex Ti-p(DDA/acac) was synthesized by reacting an amphiphilic copolymer (p(DDA/acac)) with a titanium complex. Its ultrathin films were prepared using the Langmuir-Blodgett (LB) technique. The monolayer was found to be free from hydrolysis and cross-linking side reactions, even at the air-water interface. The transferred LB films (nanosheets) were oxidized by ultraviolet irradiation at room temperature. The photo-oxidized material has an amorphous and porous structure with subnanometer-scale controllability (0.18 nm per layer). Photocatalytic performance was demonstrated by converting multilayered LB films of Ti-(DDA/acac) and the silicon-containing polymer p(DDA/SQ) into ultrathin hetero-multilayers of TiO2 and SiO2 under UV-O3 treatment. The scalability affords a uniform photopattern formation of photo-oxidized TiO2 films over several hundreds of micrometers.

Dynamics of Chiral Cations in Two-Dimensional CuX4 and PbX4 Perovskites (X = Cl and Br).

Chiral organic ammonium cations ((R)-2-methylphenethylammonium (R-MPhA) and (R)-3,7-dimethyloctylammonium (R-DMOA)) cations were combined with [MX4]2- anions (M = Cu and Pb, X = Cl and Br) to form two-dimensional (2D) perovskites: (R-MPhA)2CuCl4 (1a), (R-MPhA)2CuBr4 (1b), (R-DMOA)2CuCl4 (2a), (R-DMOA)2CuBr4 (2b), (R-DMOA)2PbCl4 (2c), and (R-DMOA)2PbBr4 (2d). The point shearing of the MX4 octahedron formed 2D perovskite layers, which were sandwiched by the bilayer molecular assembly of chiral organic ammonium cations. We found that the flexible and polar organic R-MPhA and R-DMOA cations in the 2D perovskites played an important role in the phase transition behavior and dielectric responses. Salts 2a-2d showed similar solid-solid (S1-S2) phase transitions, for which the temperatures decreased in the order of CuCl4 (2a) > PbCl4 (2c) > CuBr4 (2b) > PbBr4 (2d). The occupation volume of one R-DMOA per MX4 octahedron determined the dynamic crystalline space for the motional freedom of chiral ammonium in the 2D perovskite layer. Although thermally activated dielectric fluctuations were observed in salts 2a, 2b, and 2c, only an order-disorder-type dielectric phase transition was observed in salt 2d. Interband optical transitions were observed in the CuCl4 and CuBr4 2D perovskites, whereas sharp exciton absorptions were observed in the 2D PbCl4 and PbBr4 layers in perovskite salts 2c and 2d.

Contrasting temperature dependences of isostructural one-dimensional ferroelectric crystals NH4HSO4 and RbHSO4 in terms of thermal conductivities.

Temperature-dependent thermal conductivities are reported for one-dimensional (1D) hydrogen-bonding ferroelectric crystals of isostructural compounds NH4HSO4 and RbHSO4. As the temperature was decreased from 300 K, at which point they were paraelectric in the P21/n space group, their thermal conductivities decreased, similar to those of glassy materials. At the ferroelectric transition points (T1A = 270 K for NH4HSO4 and T1R = 264 K for RbHSO4), a change from P21/n to Pn space groups was observed, and the thermal conductivity of the NH4HSO4 crystal decreased without any anomalies, whereas that of RbHSO4 increased, similar to that of crystalline materials. At the second ferroelectric-to-paraelectric transition point of NH4HSO4 (T2A = 154 K), the thermal conductivity increased from 1.00 W m-1 K to 1.32 W m-1 K and increased with a subsequent decrease in temperature, similar to that of crystalline materials. Single-crystal x-ray structure analyses revealed that the thermal conductivity transition of RbHSO4 at T1R = 264 K corresponds to the rotational motion excitation of the HSO4 - chains. The abrupt thermal conductivity jump of NH4HSO4 was likely related to the order-disorder type transition in NH4 + ions, accompanied by lattice vibration excitation, coupled with internal rotation. At the T2A ferroelectric-to-paraelectric phase transition of NH4HSO4, 21 crystal symmetry recovery was observed, similar to the Rochelle salt, and the space group at low temperatures was P21/n. For the RbHSO4 crystals, the thermal conductivity parallel to the 1D chains was 1.5-times higher than the corresponding perpendicular orientation.

Structural Phase Transitions of a Molecular Metal Oxide.

The structural phase of a metal oxide changes with temperature and pressure. During phase transitions, component ions move in multidimensional metal-oxygen networks. Such macroscopic structural events are robust to changes in particle size, even at scales of around 10 nm, and size effects limiting these transitions are particularly important in, for example, high-density memory applications of ferroelectrics. In this study, we examined structural transitions of the molecular metal oxide [Na@(SO3 )2 (n-BuPO3 )4 MoV 4 MoVI 14 O49 ]5- (Molecule 1) at approximately 2 nm by using single-crystal X-ray diffraction analysis. The Na+ encapsulated in the discrete metal-oxide anion exhibited a reversible order-disorder transition with distortion of the Mo-O molecular framework induced by temperature. Similar order-disorder transitions were also triggered by chemical pressure induced by removing crystalline solvent molecules in the single-crystal state or by substituting the countercation to change the molecular packing.

Inserting Nitrogen: An Effective Concept To Create Nonplanar and Stimuli-Responsive Perylene Bisimide Analogues.

Establishing design principles to create nonplanar π-conjugated molecules is crucial for the development of novel functional materials. Herein, we describe the synthesis and properties of dinaphtho[1,8-bc:1',8'-ef]azepine bisimides (DNABIs). Their molecular design is conceptually based on the insertion of a nitrogen atom into a perylene bisimide core. We have synthesized several DNABI derivatives with a hydrogen atom, a primary alkyl group, or an aryl group on the central nitrogen atom. These DNABIs exhibit nonplanar conformations, flexible structural changes, and ambipolar redox activity. The steric effect around the central nitrogen atom substantially affects the overall structures and results in two different conformations: a nonsymmetric bent conformation and a symmetric twisted conformation, accompanied by a drastic change in electronic properties. Notably, the nonsymmetric DNABI undergoes unique structural changes in response to the application of an external electric field, which is due to molecular motions that are accompanied by an orientational fluctuation of the dipole moment. Furthermore, the addition of a chiral Brønsted base to N-unsubstituted DNABI affords control over the helical chirality via hydrogen-bonding interactions.

Ferroelectric Alkylamide-Substituted Helicene Derivative with Two-Dimensional Hydrogen-Bonding Lamellar Phase.

Alkylamide (-CONHC nH2 n+1)-substituted benzene and its pyrene derivatives have shown a discotic hexagonal columnar liquid-crystalline phase through a one-dimensional (1D) intermolecular N-H···O═ hydrogen-bonding interaction, the direction of which is inverted through the application of an alternate current voltage. The polar hydrogen-bonding chains and dipole inversion reveal a ferroelectric polarization-electric field ( P- E) hysteresis curve. Non-π-planar helicene derivatives bearing two -CONHC14H29 chains also indicate a ferroelectric response. The racemic helicene derivative shows a bilayer lamellar liquid-crystal phase within a temperature range of 330-420 K, whereas there is no liquid crystallinity for the optically active derivative because of the different molecular assembly structure. The racemic phase is constructed through a two-dimensional (2D) N-H···O═ hydrogen-bonding network, which shows ferroelectric P- E hysteresis curves at above 340 K. The collective dipole inversion in the 2D layer contributes to the ferroelectricity in the lamellar phase. The remanent polarization ( Pr) of 11.1 µC cm-2 is about 6 times higher than those of the π-planar benzene- and pyrene-based 1D ferroelectrics. Both the density of the hydrogen-bonding site and the domain orientation in the 2D system are higher than those of the 1D columnar system.

Selective Formation of a Mixed-Valence State from Linearly Bridged Oligo(aromatic diamines): Drastic Structural Change into a Folded Columnar Stack for Half-filled Polycations.

A method to obtain an organic mixed-valence state with long-range delocalization is proposed, which enables the selective generation of half-filled (n/2-charged) polycations from linearly bridged oligomers with n electron-donating units. When π-extended phenylenediamine units are connected by meta-xylylene-type spacers, the resulting oligomers adopt non-folded structures in the neutral state owing to the non-conjugating and flexible nature of the spacer, whereas the structure shows a drastic change into a one-dimensional columnar stack upon oxidation to the corresponding half-filled polycations. Although they are nano-sized discrete molecules, they can mimic the electronic structure of crystalline organic conductors in a mixed-valence state. The key for the oligomer design is adoption of the best-matched spacer that facilitates formation of the singly charged pimer in the dichromophoric system whereas the corresponding doubly charged π-dimer is disfavored.