Design and Synthesis of Hydroxide Ion–Conductive Metal–Organic Frameworks Based on Salt Inclusion

We demonstrate a metal–organic framework (MOF) design for the inclusion of hydroxide ions. Salt inclusion method was applied to an alkaline-stable ZIF-8 (ZIF = zeolitic imidazolate framework) to introduce alkylammonium hydroxides as ionic carriers. We found that tetrabutylammonium salts are immobilized inside the pores by a hydrophobic interaction between the alkyl groups of the salt and the framework, which significantly increases the hydrophilicity of ZIF-8. Furthermore, ZIF-8 including the salt exhibited a capacity for OH^– ion exchange, implying that freely exchangeable OH^– ions are present in the MOF. ZIF-8 containing OH^– ions showed an ionic conductivity of 2.3 × 10^–8 S cm^–1 at 25 °C, which is 4 orders of magnitude higher than that of the blank ZIF-8. This is the first example of an MOF-based hydroxide ion conductor

Design and Synthesis of Hydroxide Ion–Conductive Metal–Organic Frameworks Based on Salt Inclusion

We demonstrate a metal–organic framework (MOF) design for the inclusion of hydroxide ions. Salt inclusion method was applied to an alkaline-stable ZIF-8 (ZIF = zeolitic imidazolate framework) to introduce alkylammonium hydroxides as ionic carriers. We found that tetrabutylammonium salts are immobilized inside the pores by a hydrophobic interaction between the alkyl groups of the salt and the framework, which significantly increases the hydrophilicity of ZIF-8. Furthermore, ZIF-8 including the salt exhibited a capacity for OH^– ion exchange, implying that freely exchangeable OH^– ions are present in the MOF. ZIF-8 containing OH^– ions showed an ionic conductivity of 2.3 × 10^–8 S cm^–1 at 25 °C, which is 4 orders of magnitude higher than that of the blank ZIF-8. This is the first example of an MOF-based hydroxide ion conductor

Silapillar[<i>n</i>]arenes: Their Enhanced Electronic Conjugation and Conformational Versatility

During recent decades, methylene-bridged macrocyclic arenes have been widely used in supramolecular chemistry. However, their π-conjugations are very weak, as the methylene bridges disrupt the electronic communication between π orbitals of the aromatic units. Herein, we successfully synthesized a series of silapillar[n]arenes (n = 4, 6, and 8) using silylene bridging. These showed enhanced electronic conjugation compared with the parent pillar[n]arenes because of σ*−π* conjugation between σ* (Si–C) orbitals and π* orbitals of the benzenes. Owing to the longer Si–C bond compared with the C–C bond, silylene-bridging provides additional structural flexibility into the pillar[n]arene scaffolds; a strained silapillar[4]arene was formed, which is unavailable in the parent pillar[n]arenes because of the steric requirements. Furthermore, silapillar[n]arenes displayed interesting size-dependent structural and optical properties

Donor/Acceptor Segregated π‑Stacking Arrays by Use of Shish-Kebab-Type Polymeric Backbones: Highly Conductive Discotic Blends of Phthalocyaninatopolysiloxanes and Perylenediimides

Construction of large-area electron donor–acceptor (D–A) interfaces and hole/electron pathways is important for photoconducting and photovoltaic functions. Although blends of D- and A-type discotic π-systems have a possibility to realize one-dimensional charge carrier pathways as well as heterointerfaces, D–A segregated structures are difficult to develop by self-assembly because they are entropically unfavored structures. Here we report the use of shish-kebab-type hole-transporting discotic columns fixed by a self-threading polysiloxane chain and approach to such segregated nanostructures. Electron-donor/acceptor blends of soluble phthalocyaninato­polysiloxanes (Poly-SiPcs) and perylenedicarboximides (PDIs) were prepared, and their photoconductive property was investigated. Although <b>Poly-SiPc1</b> shows a photoinduced charge separation with <b>PDI1</b> analogous to the corresponding monomeric phthalocyanines (<b>SiPc1</b> and <b>H</b>_<b>2</b><b>Pc1</b>), the <b>Poly-SiPc1</b>/<b>PDI1</b> system displays a remarkably larger photoconductivity than <b>SiPc1/PDI1</b> and <b>H</b>_<b>2</b><b>Pc1</b>/<b>PDI1</b>, which mostly results from the presence of hole-transporting pathways with the mobility μ_h,1D ∼ 0.1 cm² V^–1 s^–1 in <b>Poly-SiPc1</b> along the polysiloxane covalent bonds even upon mixing with <b>PDI1</b>. When π-stackable <b>PDI2</b> is used instead of <b>PDI1</b>, X-ray diffraction analysis disclosed obvious signs of π-stacking periodicities for both Pc and PDI planes in the mixture, indicating the presence of donor–acceptor segregated domains of columnar structures. As a result, photoexcitation of <b>Poly-SiPc1</b>/<b>PDI2</b> generates highly mobile holes and electrons, leading to the observation of a much larger conductivity

Exciplex Formation by Complexation of an Electron-Accepting Guest in an Electron-Donating Pillar[5]arene Host Liquid

We present a novel system, a liquid-state pillar[5]arene decorated with tri(ethylene oxide) chains, that brings electron-donor and electron-acceptor molecules into proximity for efficient exciplex formation. The electron-accepting guests exhibit a blue–purple emission from a localized excited state upon excitation in common solvents. However, directly dissolving the guests in the electron-donating pillar[5]arene liquid (a bulk system) results in visible green emission from the formed exciplexes. In the bulk system, the guest molecules are always surrounded by excess pillar[5]arene molecules, resulting in the formation of mainly inclusion-type exciplexes. In the bulk system, energy migration occurs between the pillar[5]arene molecules. Excitation of the pillar[5]arenes results in a more intense green exciplex emission than that observed upon direct excitation of the guests. In summary, the pillar[5]arene liquid is a novel system for achieving efficient exciplex formation and energy migration that is different from typical solvent and solid systems

Segregated and Alternately Stacked Donor/Acceptor Nanodomains in Tubular Morphology Tailored with Zinc Porphyrin–C₆₀ Amphiphilic Dyads: Clear Geometrical Effects on Photoconduction

Amphiphilic zinc porphyrin (P_Zn; electron donor, D)–fullerene (C₆₀; electron acceptor, A) dyads <b>2</b> and <b>3</b>, bearing an identical hydrophilic wedge with triethylene glycol chains but different linkers between the P_Zn and C₆₀ units, self-assemble into nanotubes with essentially different dimensional and geometrical features from one another. The nanotube from dyad <b>2</b> with an ester linker consists of a bilayer wall formed with coaxially segregated D and A nanodomains along the tube axis (coaxial D–A heterojunction), thereby displaying explicit photoconductivity with ambipolar carrier transport properties. In contrast, the nanotube from dyad <b>3</b> with a rigid arylacetylene linker consists of a monolayer wall with an alternate geometry of D/A stacking, resulting in poor photoconducting outputs. Such a geometrical difference also significantly affects the photovoltaic properties

Propeller-Shaped Fused Oligothiophenes: A Remarkable Effect of the Topology of Sulfur Atoms on Columnar Stacking

Propeller-shaped regioisomers of fused oligothiophenes <b>F9T</b>_<b>endo</b>, <b>F9T</b>_<b>anti</b>, and <b>F9T</b>_<b>exo</b> were successfully synthesized. DFT calculations indicated that their core parts are distorted from planarity due to intramolecular steric repulsions involving large sulfur atoms. In contrast with soft crystalline <b>F9T</b>_<b>anti</b> and <b>F9T</b>_<b>exo</b>, <b>F9T</b>_<b>endo</b> self-assembles into a hexagonal columnar liquid crystal (Col_h LC), displaying a clear X-ray diffraction (XRD) due to its stacked π-conjugated core. In each LC column, well-organized intermolecular S–S contacts are developed triple-helically along the columnar axis with a helical pitch of 4.04 nm. Among LC semiconductors reported to date, Col_h LC <b>F9T</b>_<b>endo</b> displays a top-class charge-carrier mobility (0.18 cm² V^–1 s^–1) with a distinct ambipolar character featuring well-balanced hole and electron mobilities. A thin film, prepared by mixing <b>F9T</b>_<b>endo</b> with soluble fullerene PCBM, shows a photovoltaic response, when the fullerene content is large enough to compensate a small absorptivity of <b>F9T</b>_<b>endo</b> for visible light

Continuous Control of Optical Gaps in Quasi-One-Dimensional Bromide-Bridged Platinum Complexes by Utilizing Chemical Pressure

The optical gap in a series of bromo-bridged platinum chain complexes, [Pt­(en)₂Br]­(C_<i>n</i>–Y)₂·H₂O (en = ethylenediamine; C_<i>n</i>–Y = dialkyl sulfosuccinate; <i>n</i> = the number of carbon atoms), was controlled by using chemical pressure. From the single-crystal structure, [Pt­(en)₂Br]­(C₆–Y)₂·H₂O is in a mixed-valence state at 200 K. In addition, Pt–Pt distances decreased with an increase in <i>n</i> or with a decrease in the temperature. Continuous decreases in the optical gaps upon cooling were observed for <i>n</i> = 5, 7. The smallest gap of 1.20 eV was observed for <i>n</i> = 7 at 50 K. For <i>n</i> = 12, the complex was still in a mixed-valence state at 5 K, although the Pt–Pt distance was quite short. This is probably because of the energetic mismatch between 5d_<i>z</i>² orbitals of the Pt ions and 4p_<i>z</i> orbitals of the Br ions

Shape-Dependent Hydrogen-Storage Properties in Pd Nanocrystals: Which Does Hydrogen Prefer, Octahedron (111) or Cube (100)?

Pd octahedrons and cubes enclosed by {111} and {100} facets, respectively, have been synthesized for investigation of the shape effect on hydrogen-absorption properties. Hydrogen-storage properties were investigated using in situ powder X-ray diffraction, in situ solid-state ²H NMR and hydrogen pressure–composition isotherm measurements. With these measurements, it was found that the exposed facets do not affect hydrogen-storage capacity; however, they significantly affect the absorption speed, with octahedral nanocrystals showing the faster response. The heat of adsorption of hydrogen and the hydrogen diffusion pathway were suggested to be dominant factors for hydrogen-absorption speed. Furthermore, in situ solid-state ²H NMR detected for the first time the state of ²H in a solid-solution (Pd + H) phase of Pd nanocrystals at rt

Nanosize-Induced Drastic Drop in Equilibrium Hydrogen Pressure for Hydride Formation and Structural Stabilization in Pd–Rh Solid-Solution Alloys

We have synthesized and characterized homogeneous solid-solution alloy nanoparticles of Pd and Rh, which are immiscible with each other in the equilibrium bulk state at around room temperature. The Pd–Rh alloy nanoparticles can absorb hydrogen at ambient pressure and the hydrogen pressure of Pd–Rh alloys for hydrogen storage is dramatically decreased by more than 4 orders of magnitude from the corresponding pressure in the metastable bulk state. The solid-solution state is still maintained in the nanoparticles even after hydrogen absorption/desorption, in contrast to the metastable bulks which are separated into Pd and Rh during the process