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An Electrochemical Cholesteric Liquid Crystalline Device for Quick and Low-Voltage Color Modulation

We demonstrate a method for fabricating a prototype reflective display device that contains cholesteric liquid crystal (LC) as an active component. The ...

The University of Tokyo

the university of tokyo

Indium-catalyzed cycloisomerization of omega-alkynyl-beta-ketoesters into six- to fifteen-membered rings.

Treatment of an (o-alkynylphenyl)phosphine with a stoichiometric amount of BuLi effects a cyclization reaction to produce a 3-lithiobenzo[b]phosphole, which affords a variety of 3-substituted benzophospholes upon reaction with electrophiles. An example is given for the synthesis of a bis-benzo[b]phosphole, which can be further converted to the corresponding benzo[b]phosphole oxide possessing high electron affinity.

Modular synthesis of benzo[b]phosphole derivatives via BuLi-mediated cyclization of (o-alkynylphenyl)phosphine.

Lewis acidic indium(III) salts, in particular In(NTf(2))(3), effect the conversion of alpha-(omega'-alkynyl)-beta-ketoesters and omega-alkynyl-beta-ketoesters to the corresponding cyclic products in a manner known as the Conia-ene reaction. This reaction can lead to the creation of five- to fifteen-membered-ring carbocycles and heterocycles in good to excellent yields. The synthetic features of the reaction are a relatively low catalyst loading, as low as 0.01 mol % in the best case, as well as no requirement of solvent for five-membered-ring formation and the requirement of only moderately dilute reaction conditions for medium-sized-ring formation. The high reactivity of indium salts is due to the double activation of the beta-ketoester substrate containing an acetylene function. The indium metal activates the beta-ketoester moiety by the formation of an indium enolate, and this indium metal electrophilically activates the alkyne moiety. Such a strong push-pull activation of the substrate by a single metal circumvents the disadvantage of entropic and enthalpic factors generally associated with the formation of medium- and large-sized rings. The reaction allows the ready formation of a fifteen-membered-ring carbocycle, from which dl-muscone has been synthesized.

Efficient formation of ring structures utilizing multisite activation by indium catalysis.

Being inspired by naturally occurring peptidic macrocycles, we developed liquid-crystalline (LC) compounds 1 and 2 that are capable of self-assembling into hexagonal columnar mesophases over a wide temperature range that includes room temperature. Their bowl-shaped macrocyclic cores are conformationally robust because of the presence of internal H-bonds, while the columnar assembly is ensured by intermolecular H-bonding interactions involving the exocyclic amide units. When an electric field was applied to their LC films from a direction orthogonal to the film plane, the columns were oriented homeotropically over a large area.

Columnarly assembled liquid-crystalline peptidic macrocycles unidirectionally orientable over a large area by an electric field.

Over the past decade, major progress in supramolecular polymerization has had a substantial effect on the design of functional soft materials. However, despite recent advances, most studies are still based on a preconceived notion that supramolecular polymerization follows a step-growth mechanism, which precludes control over chain length, sequence, and stereochemical structure. Here we report the realization of chain-growth polymerization by designing metastable monomers with a shape-promoted intramolecular hydrogen-bonding network. The monomers are conformationally restricted from spontaneous polymerization at ambient temperatures but begin to polymerize with characteristics typical of a living mechanism upon mixing with tailored initiators. The chain growth occurs stereoselectively and therefore enables optical resolution of a racemic monomer. 

Noncovalent assembly. A rational strategy for the realization of chain-growth supramolecular polymerization.

Polar interactions such as electrostatic forces and hydrogen bonds play an essential role in biological molecular recognition. On a protein surface, polar interactions occur mostly in a hydrophobic environment because nonpolar amino acid residues cover ~75% of the protein surface. We report that ionic interactions on a hydrophobic surface are modulated by their subnanoscale distance to the surface. We developed a series of ionic head groups-appended self-assembled monolayers with C2, C6, C8, and C12 space-filling alkyl chains, which capture a dendritic guest via the formation of multiple salt bridges. The guest release upon protonolysis is progressively suppressed when its distance from the background hydrophobe changes from 1.2 (C2) to 0.2 (C12) nanometers, with an increase in salt bridge strength of ~3.9 kilocalories per mole.

Ionic interactions. Subnanoscale hydrophobic modulation of salt bridges in aqueous media.

The first design strategy that allows both memorization and modulation of the liquid-crystalline reflection color is reported. Electrophoretic deposition of a tailored ionic chiral dopant is key to realizing this unprecedented function, which may pave the way for the development of full-color e-paper that can operate without the need of color filters.

Electrophoretic Deposition for Cholesteric Liquid-Crystalline Devices with Memory and Modulation of Reflection Colors.

Crystals of pyrene tweezers 1 with interdigitating pyrenyl blades jump vigorously at around 160 °C. Single-crystal X-ray diffraction analysis before jumping revealed the presence of a "pyrene tetrad" in the crystal lattice, where four pyrenyl blades are π-stacked on top of each other. Upon heating the crystal to induce the jumping event, inner two pyrenyl blades in the "pyrene tetrad" probably rotate to switch off their π-stacking interaction with the neighboring outer pyrenyl blades and form new CH-π bonds. Different from reported salient crystals, our crystal jumps with the release of CHCl as inclusion solvent.

Jumping Crystals of Pyrene Tweezers: Crystal-to-Crystal Transition Involving π/π-to-CH/π Assembly Mode Switching.

For the concept of aromaticity, energetic quantification is crucial. However, this has been elusive for excited-state (Baird) aromaticity. Here we report our serendipitous discovery of two nonplanar thiophene-fused chiral [4n]annulenes  COT  and  CDH  , which by computational analysis turned out to be a pair of molecules suitable for energetic quantification of Baird aromaticity. Their enantiomers were separable chromatographically but racemized thermally, enabling investigation of the ring inversion kinetics. In contrast to  CDH  , which inverts through a nonplanar transition state, the inversion of  COT  , progressing through a planar transition state, was remarkably accelerated upon photoexcitation. As predicted by Baird's theory, the planar conformation of  COT  is stabilized in the photoexcited state, thereby enabling lower activation enthalpy than that in the ground state. The lowering of the activation enthalpy, i.e., the energetic impact of excited-state aromaticity, was quantified experimentally to be as high as 21-22 kcal mol.Baird's rule applies to cyclic π-conjugated molecules in their excited state, yet a quantification of the involved energetics is elusive. Here, the authors show the ring inversion kinetics of two nonplanar and chiral [4n]annulenes to support Baird's rule from an energetic point of view.

Energetics of Baird aromaticity supported by inversion of photoexcited chiral [4n]annulene derivatives.

Water dynamics: Gliding and trudging.

Electric double layer (EDL) capacitors are promising as next-generation energy accumulators if their capacitances and operation voltages are both high. However, only few electrolytes can simultaneously fulfill these two requisites. Here we report that an oligomeric ionic liquid such as IL4with four imidazolium ion units in its structure provides a wide electrochemical window of ∼5.0 V, similar to monomeric ionic liquids. Furthermore, electrochemical impedance measurements using Au working electrodes demonstrated that IL4exhibits an exceptionally high EDL capacitance of ∼66 μF/cm, which is ∼6 times as high as those of monomeric ionic liquids so far reported. We also found that an EDL-based field effect transistor (FET) using IL4as a gate dielectric material and SrTiOas a channel material displays a very sharp transfer curve with an enhanced carrier accumulation capability of ∼64 μF/cm, as determined by Hall-effect measurements.

Exceptionally High Electric Double Layer Capacitances of Oligomeric Ionic Liquids.

Here, we report the first redox-active chiral dopant D, which electrically alters its helical twisting power (HTP) for a cholesteric liquid crystalline (LC) medium and quickly changes the reflection color. D is composed of an axially chiral binaphthyl unit in conjunction with a redox-active ferrocene unit. A cholesteric LC phase of 4'-pentyloxy-4-cyanobiphenyl, doped with D (3.0 mol %), developed a blue reflection color. When nitrosyl tetrafluoroborate, a one-electron oxidant, was added to this cholesteric LC phase, D was oxidized to decrease its original HTP value by 13%, so that a green reflection color was developed. In the presence of a supporting electrolyte, the reflection color was electrochemically modulated using a sandwich-type glass cell with indium tin oxide electrodes. In quick response to the applied voltage of +1.5 V, the reflection color changed from blue to green within 0.4 s. When 0 V was applied, the reflection color returned to its original blue color. The D-doped cholesteric LC is characterized by its fastest electrochemical response and lowest operating voltage among those reported for electrically driven cholesteric LC devices.

Redox-Responsive Chiral Dopant for Quick Electrochemical Color Modulation of Cholesteric Liquid Crystal.

Disk- and rod-shaped molecules are incompatible in coassembly, as the former tend to stack one-dimensionally whereas the latter tend to align in parallel. Because this type of incompatibility can be more pronounced in condensed phases, different-shaped molecules generally exclude one another. We report that supramolecular polymerization of a disk-shaped chiral monomer in nematic liquid crystals comprising rod-shaped molecules results in order-increasing mesophase transition into a single mesophase with a core-shell columnar geometry. This liquid crystalline material responds quickly to an applied electric field, resulting in unidirectional columnar ordering. Moreover, it can be modularly customized to be optoelectrically responsive simply by using a photoisomerizable rod-shaped module. The modular strategy allows for cooperative integration of different functions into elaborate dynamic architectures.

Yoshimitsu Itoh

Department of Chemistry and Biotechnology

The University of Tokyo

An Electrochemical Cholesteric Liquid Crystalline Device for Quick and Low-Voltage Color Modulation

Yoshimitsu Itoh

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Chemistry and Biotechnology

The University of Tokyo

An Electrochemical Cholesteric Liquid Crystalline Device for Quick and Low-Voltage Color Modulation

Department of Chemistry and Biotechnology