Kyosuke Isoda

Truxene‐Based Columnar Liquid Crystals: Self‐Assembled Structures and Electro‐Active Properties

Columnar liquid-crystalline (LC) truxene derivatives containing branched flexible alkyl chains have been designed and synthesized. The dicyanomethylene and dithiafulvene substituents have been introduced into the pi-conjugated truxene framework to tune their electronic and redox properties as well as the molecular assembled structures. The pi-conjugated cores of dicyanomethylene- and dithiafulvene-appended truxenes adopt bowl-shaped conformations, giving rise to a large intrinsic dipole moment perpendicular to the aromatic framework. These molecules form stable columnar LC structures through intermolecular dipole-dipole interactions. The redox properties of LC truxene derivatives have been examined by cyclic voltammetry. The dicyanomethylene-appended truxene shows the reversible four-step electrochemical reductions, whereas the dithiafulvene-appended truxene undergoes three-step oxidations.

Dipole-driven self-assembly of redox-active mesogenic tetracyanoanthraquinodimethanes

Tetracyanoanthraquinodimethane (TCAQ) derivatives having three alkoxy chains at their extremities self-assemble to form both columnar liquid crystals and fibrous aggregates through intermolecular dipole–dipole interactions. The TCAQ derivatives are redox-active, and they exhibit responses in electrochromism in the reductive potential region.

Electron Transport of Photoconductive n‐Type Liquid Crystals Based on a Redox‐Active Tetraazanaphthacene Framework

The preparation of two liquid crystals composed of a redox-active tetraazanaphthacene (TANC) framework is reported. The materials form smectic A (SmA) thin-film liquid-crystalline (LC) phases over a wide temperature range. Cyclic voltammetry analysis revealed that LC TANCs behave as organic electron acceptors. The electron mobilities of the thin films were determined by time- of-flight (TOF) measurements, which are the order of 10(-4)  cm(2)  V(-1)  s(-1) in the SmA LC phase. This value is two orders of magnitude larger than those of amorphous organic semiconductors. To the best of our knowledge, very few reports exist on the electron-transporting behaviors of LC N-heteroacene semiconductors.

Room-temperature redox-active liquid crystals composed of tetraazanaphthacene derivatives.

Ordered superstructures fabricated by self-organization can be achieved through programmed molecular design, using non-covalent intermolecular interactions such as hydrogen bonding, coordination, electrostatic attraction, and van der Waals forces at equilibrium in the experimental system. A liquid-crystalline (LC) state constructed from assembled molecules can form self-organized superstructures even in thin films because the arrangement of molecules in the LC state already forms an ordered superstructure by intermolecular interactions such as the hydrophobic attraction of long alkyl chains. Some LC molecules with p-conjugated polycyclic frameworks and certain long-chain alkyl substituents not only self-organize into low-dimensional ordered superstructures but also have a high charge-carrier mobility through the p-stacking structures when a bias voltage is applied. Further, LC molecule have the potential to compensate for high carrier-transport through an ordered superstructure in the LC films because of a selfhealing behavior which reduces grain boundaries and structural defects by molecular fluctuation. Interestingly, N-heteroacenes, in which N atoms partially replace C atoms in a p-conjugated polycyclic oligoacene framework (e.g., pentacene), behave as electron acceptors due to the presence of electronegative imino-N atoms. These compounds are therefore good candidates for n-type semiconductors capable of transporting electrons. 5,6,11,12Tetraazanaphthacene (TANC), an N-heteroacene with four N atoms that was previously reported by our group, also functions as an electron acceptor, having reversible two-step, two-electron transfer peaks (E1/2 = 0.66 V and E1/2 = 1.20 V vs. Ag/Ag in acetonitrile). We also observed a field-effect transistor (FET) activity for a TANC thin film prepared by a vapor deposition process. However, the FET activity decreased due to the independent and isolated growth of crystalline domains on the surface over time. A molecular conductor with high conductivity (50 Scm 1 at room temperature), formed from TANC radical anions and copper ions, has been also reported. The TANC radical anions, as bridging ligands, coordinate to Cu ions present in mixed valence states (Cu/Cu) to produce a conductive metal-coordination polymer with d–p interactions similar to the Cu-Me2DCNQI system. [21] Herein, we have investigated the effects of the introduction of long alkyl chains into TANC and fluoflavin (FFV, a reduced precursor of TANC), which develop LC states based on their p-conjugated frameworks. By these modifications, we are able to prepare two redox-active room-temperature LC materials: 1 a with an oxidized TANC framework and 2 a with a reduced FFV skeleton. Thin films with columnar molecular arrays are easily fabricated from these LC materials, in which 1 a and 2 a are aligned parallel to the shearing direction by application of a shearing mechanical stress. Moreover, upon the addition of the strong base 1,8diazabicycloundec-7-ene (DBU), a mixture of 1 a and 2 a generates a TANC radical anion by the disproportionation of an electron from the FFV to the TANC framework. To the best of our knowledge, for an N-heteroacene framework, only a smectic LC state based on dipole moments has been reported. However, this is the first report on the formation of the columnar LC state of 1 a and 2 a at room temperature through self-organization. Figure 1 shows the molecular structures of 1 and 2 bearing racemic branched alkoxy chains a and linear chains b at the

DNA terminal mismatch-induced stabilization of polymer micelles from RAFT-generated poly(N-isopropylacrylamide)-DNA block copolymers

Temperature-responsive diblock copolymers made of poly(N-isopropylacrylamide) (PNIPAAm) generated by reversible addition-fragmentation chain transfer (RAFT) polymerization and a single-stranded DNA (ssDNA) self-assembled into polymer micelles. The micelles consisted of the PNIPAAm core surrounded by the ssDNA corona with a hydrodynamic diameter up to 300 nm in an aqueous medium above the lower critical solution temperature. In a medium of high ionic strength, the formation of the fully matched duplex with the complementary ssDNA on the surface of the polymer micelles induced rapid and spontaneous aggregation. By contrast, the micelles remained dispersed under the identical conditions when single-base-substituted ssDNA was added to form the corresponding terminal-mismatched duplex on the micellar surface. This highly sequence-selective process took place irrespective of the size of the PNIPAAm core.

Spin Enhancement by Grinding of Cu‐TANC Coordination Polymer Crystals Showing d–π Interactions

Nanometer-scale molecular crystals undergo structural transition and subsequent destruction when pulverized in a mill and ground in a mortar, because of the mechanical force exerted on the molecular surface under conditions of high frictional heat and interfacial pressure in the mortar. Furthermore, mechanical effects, such as those caused by nanofriction, trigger molecular transformation and chemical reactions in each individual molecule in the crystals. For example, when C60 crystals are subjected to high-pressure compression in an anvil cell or shaken in a powder machine for several hours, polymers and oligomers in which the monomer units are linked by C C covalent bonds are formed. When a cellophane adhesive tape is mechanically removed from the substrate surface, strong Xrays are emitted because of the collapse of the surface atoms. Crystal grinding often results in the formation of charge-transfer (CT) complexes and metal-coordination compounds. Grinding of a mixture of quinone and hydroquinone results in the formation of quinhydrone, a CT complex in which proton and electron transfer occur. Large multicomponent molecules such as metal coordination compounds can be formed by grinding and continuous annealing of metal ions and ligands. Thus, the grinding operation generates very high energy that can be used to synthesize metal complexes. Furthermore, it is forced to specific softening applications of mechanochemical synthesis, such as the use of liquid-assisted grinding to screen for cocrystal formation. We propose a novel method for enhancing the spin intensity of the signals in the ESR spectrum of the mortar-ground powder of the coordination polymer crystal {[Cu(TANC)I]}n 1, formed from an organic electron acceptor (TANC; 5,6,11,12-tetraazanaphthacene), an electron donor (Cu), and I ions. The spin intensity enhancement is probably due to the increased formation of spin-active species, TANC radical anions and Cu ions, from crystal defects and by crystal transformation. The design of highly conductive coordination polymers is difficult because of the large band gap between the metal ions and the organic bridged ligands. We have previously reported a new highly conductive Cu coordination polymer containing TANC, the N atoms of which can directly coordinate with a Cu ion in a conjugated ring framework. The electrons in the HOMO of the Cu ion can be transferred to the LUMO of TANC by CT, as in the case of N,N’-dicyanoquinonediimine (DCNQI) and tetracyanoquinodimethane (TCNQ). Most of the Cu-TANC complexes, irrespective of whether they are electron-conductive or not, form black crystals owing to CT interactions. Slow mixing of TANC and CuI in MeCN affords 1 as black prismatic crystals. Figure 1 a and Figure 1 b show the crystal structure of 1: zigzag ribbon polymers are formed along the b axis by the bridging of Cu ions by TANC. Figure 1 c also shows the periodic molecular arrangement in a polymer chain with the appropriate numbering scheme. Each unit has a tridentate coordination sphere in which a central Cu ion is coordinated by two N atoms (from two TANC moieties) and an I ion. The bond distances and angles around the coordination sphere are as follows: Cu(1) N(1) = 1.9454(9) , Cu(1) I(1) = 2.5219(3) , N(1) Cu(1) N(3)* = 125.89(7)8, N(1) Cu(1) I(1) = 126.58(10)8, N(3) Cu(1) I(1) = 107.52(7)8 (*: ( x + 3/2, y 1/2, z)). The Cu(1) N(2) distance (3.51(1) ) is relatively long and cannot be related to the coordination sphere. The closest Cu Cu distances through the bridging TANC units are 7.01 and 7.20 in the intrachains and interchains of coordination polymers, respectively. The short C C distances between the TANC stacks in different polymer chains, C(8)···C(8)* = 3.221(3) [*: ( x + 1, y, z)] and C(2)···C(14)* = 3.314(2) [*:(x 1/2, y, z + 1/2)] , indicate relatively weak stacking interactions between the TANC units. X-ray photoelectron spectroscopy (XPS) measurements for the Cu valence state reveal that 1 is formed from the coordination polymers containing Cu ions and that it is almost nonconductive (s<10 9 S cm ). Figure 2 shows the Q-band ESR spectrum of 1 at 10 K. Powder crystals of Cu complexes are usually ESR-silent because of the closed-shell d configuration of Cu. However, 1 is ESR-active, probably because of the terminal radicals in the polymer, which are formed by CT interactions in the crystal defects. The aforementioned ESR spectrum shows peaks due to the TANC radical ([TANC] ) (g?= 2.0069, gk= 2.0100) and coupling of a spin to the anisotropic Cu + orbital motion in the dx2 y2 basal (ground) state (g?= 2.0590, gk= 2.2400). [12] The presence of a Cu + ion is indicated by the triplet-state peak (magnetic field: 10890 G) generated by weak out-of-plane [a] Prof. M. Tadokoro, T. Anai, T. Shinoda, A. Yamagata, Y. Kawabe, Dr. K. Isoda Department of Chemistry Faculty of Science, Tokyo University of Science Kagurazaka 1-3, Shinjuku-ku, Tokyo 162-8601 (Japan) Fax: (+ 81) 3-5261-4631 E-mail : tadokoro@rs.kagu.tus.ac.jp [b] M. Nakamura, K. Sato, Prof. D. Shiomi, Prof. T. Takui Department of Chemistry Graduate School of Science, Osaka City University Sugimoto-cho, Sumiyoshi-ku, Osaka 558-8585 (Japan) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cphc.201100489.

Acid-Responsive N-Heteroacene-Based Material Showing Multi-Emission Colors

Abstract An acid‐responsive N‐heteroacene‐based material has been prepared, which shows a blue emission color in a film. The protonation of this material in a thin film gives rise to remarkable changes in luminescent color compared to that in solution states. As the protonation of N‐heteroacene molecules in films gradually occurs, their emission color can be tuned by adjusting the exposure time of the thin films to HCl vapor.

Liquid-Crystalline and Electronic Properties of Racemic-Alkoxy Chains-Substituted Tetraazanaphthacene

We have prepared tetraazanaphthacene-based liquid crystal 1 having two racemic alkoxy chains. Compound 1 self-organizes to form the rectangular columnar liquid-crystalline phase over a wide temperature range including room temperature. However, compound 2 having two linear alkoxy chains is incapable of self-organizing superstructures. Since cyclic voltammetry revealed that 1 has two-step and two-electron reductions, 1 is expected to function as electron-transporting material.

Pre‐Melting Structure Transformation of Water Clusters in Nanoporous Molecular Crystals

Inorganic porous compounds such as mesoporous silica, zeolite, and silica gel can confine many water molecules within their hydrophilic pores. These water molecules form multi-dimensional water molecule clusters (WMCs). These clusters are thought to play an important role in enzymes and biological membranes. 2] In differential scanning calorimetry (DSC) analyses of these compounds, such nanopore-confined WMCs often show a solid–liquid phase transition, which results from a macroscopic cooperative interaction between the confined water molecules. Furthermore, the exothermic freezing peaks of WMC in the nanopores of SBA-15 and MCM-41 are separated into a few low-intensity and broadened sub-peaks. Meanwhile, the characteristic broadening of the endothermic melting peaks is attributed to pre-melting of ice near the pore walls and dependent on the pore-size distribution of the nanopores. The appearance of such sub-peaks and an unusual peak shape is not observed at the water–ice transition for bulk water. The appearance of sub-peaks is believed to result from water layers in the partially filled nanopores. The layers exist under different thermodynamic conditions as compared to boundary water at the interface between the pore wall and the WMC. 7] Herein, we report the appearance of two different broadened endothermic and exothermic sub-peak populations in DSC scans of nanotube-like WMCs. These “water nanotubes” (WNTs) are one-dimensional (1-D) channels of WMCs that exist in nanoporous H-bonding metal-coordination crystals of {[Co(H2bim)3](TMA)·20H2O}n (1; where H2bim stands for 2,2’-biimidazole and TMA stands for trimesate, see Scheme 1). Apart from a large peak at 245 K corresponding to a typical first-order phase transition from frozen ice nanotubes (INTs) to molten WNTs, in the ascending DSC curve of crystals of 1 (Figure 1), a small broadened peak can be observed at low temperature, which corresponds to a pre-melting phenomenon, usually occurring at the surface, and which results from the transition of the completely frozen WMC conformation to the INT conformation with partially moving water molecules. By solving the X-ray crystal structure of the molecular WMC at 104 K below the pre-melting transition, we show that this premelting endothermic peak results from the motion of water molecules involved in a structural transition. We previously reported the construction of a 2D H-bonded metal-coordination polymer by self-organization of tris-2,2’-biimidazole cobalt(III) ([Co(H2bim)3] 3 ) and TMA . Biimidazole metal complexes can not only form complementary intermolecular H-bonds of the dual N H···N type by mutual deprotonation, but also intermolecular H-bonds of the dual N H···O type through bonding with either of the two O atoms of a carboxyl group. The difference in acidity between the imidazolate NH group and the carboxylate COO gives rise to a strong ionic interaction, which is reinforced by two H-bonds of the electrostatic N H···O type. As such, 1D nanoporous channels of 1 form by the alternate stacking of Dand Lhexagonal sheets in a (6,3)-net. Two Dand L-chiral sheets of 1 assemble through alternating H-bonds between Dor L-[Co(H2bim)3] 3 + and TMA , as shown in Figures 1S and 2S (Supporting Information). A tube-like WNT arrangement is formed from the twenty water molecules in the periodic unit, which are stabilized by the nanopore. From X-ray crystal analysis at 296 K, despite the fact that the WNT is in the molten state, it can be observed that the electron densities of the oxygen Scheme 1. [Co(H2bim)3] 3 + and TMA .

Molecular cable-like 1-D iodic spiral chains covered with triple helices stabilized in guest-included chiral porous framework

The supramolecular crystal {[Pr(DMFA)](3)[Ni(II)(Hbim)(3)](2)I}(n) with intricate chiral networks of [Ni(II)(Hbim)(3)](-) molecules is reported. It includes a cationic architecture as a guest, constructed from chiral nanotubes that penetrate I(-) chains with spiral channels wrapped by triple helices. The I(-) chains have AC conductivity in crystals like a molecular cable.