Continuous Nanospace in Nanoporous Liquid Crystal Investigated by 129 Xe NMR Spectroscopy.

Continuous nanopores within fluid materials could be used for novel chemical events such as the accommodation of guest molecules, unique arrays of the entrapped molecules, and chemical reactions in a dynamic molecular assembly. Columnar liquid crystals composed of a one-dimensionally stacked assembly of shape-persistent macrocycles form nanochannels owing to the intrinsic nanospace in the column. However, the existence of substantial nanoporosity has not been confirmed experimentally thus far. In this study, for the first time in the literature, we confirmed the presence of discrete and spatiotemporally continuous voids in a liquid-crystalline material. In 129 Xe NMR spectroscopy of liquid crystalline columnar assembly of imine-bridged shape-persistent macrocycles under Xe atmosphere, the NMR signals of the Xe atoms entrapped in the liquid-crystalline macrocycle depended on the gas pressure and phase-transition temperatures. These results indicate that the encapsulation of Xe gas molecules within the discrete and oriented nanospaces of nanoporous liquid crystals is different from the homogeneous dissolution of the solute in an ordinary solution.

Thermally Stable Array of Discrete C60s on a Two-Dimensional Crystalline Adlayer of Macrocycles both in Vacuo and under Ambient Pressure.

A periodic monolayer array of discrete C60s was generated on an atomically flat Au(111) surface with the aid of a template adlayer. The template was a two-dimensional (2D) array of molecular pits prepared on an Au(111) surface through 2D crystallization of shape-persistent macrocycles composed of four carbazole and four salphens/Ni-salphens with a 1 nm hollow. Scanning tunneling microscopy imaging under ultra-high vacuum revealed that the square-shaped macrocycles, with 1.5 nm sides, were arranged with a periodic spacing of approximately 4.0 nm on the Au(111) surface, where the orientation and periodicity of the macrocycles were dependent on their chemical structures. After sublimation of C60s onto the adlayer, a single C60 molecule was entrapped in each pit, and an ordered molecular array of C60s was attained with a pattern similar to that of the macrocycles. The periodic pattern of C60s on the surface was thermally stable up to approximately 200 °C, even under ambient pressure. Scanning tunneling spectroscopy suggested the existence of an electronic interaction between the C60s and the Au(111) surface that was influenced by the macrocycle template on the surface.

A Light-Harvesting/Charge-Separation Model with Energy Gradient Made of Assemblies of meta-Pyridyl Zinc Porphyrins.

Self-assembly of porphyrins is a fascinating topic, not only for mimicking chlorophyll assemblies in photosynthetic organisms, but also for the potential of creating molecular-level devices. Herein, zinc porphyrin derivatives bearing a meta-pyridyl group at the meso position were prepared and their assemblies studied in chloroform. Among the porphyrins studied, one with a carbamoylpyridyl moiety gave a distinct 1 H NMR spectrum in CDCl3 , which allowed the supramolecular structure in solution to be probed in detail. Ring-current-induced chemical-shift changes in the 1 H NMR spectrum, together with vapor-pressure osmometry and diffusion-ordered NMR spectroscopy, among other evidence, suggested that the porphyrin molecules form a trimer with a triangular cone structure. Incorporation of a directly linked porphyrin-ferrocene dyad with the same assembling properties in the assemblies led to a rare example of a light-harvesting/charge-separation system in which an energy gradient is incorporated and reductive quenching occurs.

Columnar Liquid-Crystalline Macrocycles Synthesized via Metal Ion-Assisted Self-Assembly.

Columnar assemblies of liquid-crystalline (LC) macrocycles hold promise for the construction of nanochannels in fluid materials. Metal-assisted self-assembly is an efficient way to prepare LC macrocycles. A large π-conjugated ligand, 9,10-diphenylanthracene (DPA) bearing two ß-diketones, was prepared as a building unit for the macrocycle, and a series of side chains were incorporated into the DPA to yield LC materials. The bis(ß-diketone) ligands on DPA allow for the efficient formation of triangular 3:3 metallomacrocycles in the presence of square-planar Cu2+ ions. The copper-containing 3:3 metallomacrocycle with the appropriate side chains exhibited thermotropic columnar LC phases in which the columns were arranged in rectangular arrays over a wide temperature range, and well-ordered birefringent textures were observed under a polarized microscope.

Specific and Oriented Encapsulation of Fullerene C70 into a Supramolecular Double-Decker Cage Composed of Shape-Persistent Macrocycles.

An efficient strategy for the specific recognition of ellipsoidal fullerenes uses molecular containers with well-designed three-dimensional (3D) nanospaces. We describe the synthesis of a supramolecular double-decker cage composed of shape-persistent metallomacrocycles and pillar ligands. A discrete 3D nanospace was built within the molecular framework of the shape-persistent-macrocycle/bidentate-pillar molecule. The single-crystal structure of the supramolecular cage reveals a uniquely shaped inner cavity with a size and net volume (>670 Å3 ) that are well matched to the shape and size of C70 . The cage exhibited higher selectivity for C70 over C60 , the smaller carbon allotrope. We suggest that such C70 -selective recognition is derived from multiple CH-π interactions between hydrogen atoms inside the cage and C70 .

Columnar Liquid Crystals from a Giant Macrocycle Mesogen.

Columnar liquid crystals composed of a giant macrocyclic mesogen were prepared. The giant macrocyclic mesogen has a square hollow with a 2.5 nm diagonal, which was bounded by diindolo[3,2-b:2',3'-h]carbazole (diindolocarbazole) moieties as the edges and bis(salicylidene)-o-phenylenediamine (salphen) moieties as the corners. The shape and size of the macrocycle were directly observed by scanning tunneling microscopy (STM). Each side of the bright square in the STM image corresponds to a diindolocarbazole moiety, and the length of the sides was consistent with the result of the single crystal analysis of diindolocarbazole. Finally, we successfully obtained a giant macrocycle with long and branched side chains, which exhibited a rectangular columnar LC phase over a wide temperature range. To the best of our knowledge, it contained the largest discrete inner space of any thermotropic columnar liquid crystal composed of macrocyclic mesogens.

Metal-Ion-Induced Switch of Liquid-Crystalline Orientation of Metallomacrocycles.

A new series of shape-persistent imine-bridged macrocycles were synthesized based on dynamic covalent chemistry. The macrocycles had an alternating sequence of dibenzothiophene and N,N'-bis(salicylidene)-ethylenediamine (salen) tethering branched alkyl chains. The macrocycles and tetranuclear metallomacrocycles bearing long and branched alkyl chains exhibited thermotropic columnar liquid-crystalline phases over a wide temperature range and the metallomacrocycles greatly depended on the characteristics of the coordinated metal ions. The metal-free macrocycle showed a liquid-crystalline phase with a lamellar structure and poor birefringence. In sharp contrast, the macrocyclic Ni complex showed a columnar oblique liquid-crystalline phase, whereas the Pd and Cu complexes showed columnar liquid-crystalline phases with a lamellar structure. The macroscopic organization and thermal properties of the corresponding liquid-crystalline metallomacrocycles were significantly dependent on the subtle structural differences among the planar macrocycles, which were revealed by single-crystal X-ray crystallographic analysis of the macrocycles with shorter alkyl chains.

Columnar liquid-crystalline metallomacrocycles.

We report synthesis of novel macrocyclic molecules and their metal complexes as well as their thermotropic columnar liquid-crystalline behavior. The macrocyclic ligands were prepared size-selectively based on dynamic covalent chemistry. X-ray study of a model macrocycle with short alkyl chains revealed that they were discrete and highly symmetric, with an inner vacant cavity of 9 Å diameter enclosed by a 56π planar ring composed of four bis(salicylidene)-o-phenylenediamine (salphen) moieties alternating with four carbazoles. Ni(2+) and Cu(2+) ions were incorporated into the four salphen ligands and formed square-planar metal complexes inside the macrocycles. From the structural and thermal analyses via X-ray diffraction measurements, differential scanning calorimetry, and polarized optical-microscopic observations, it was revealed that the macrocyclic ligand and its metal complexes self-assembled into columnar liquid-crystalline phases depending on the temperature and displayed a highly fluid character over a wide range of temperatures. The peripheral alkyl chains were influential in controlling the temperature range and flowability of the liquid-crystalline phases, and the range of the liquid-crystalline temperature of the metallo-macrocycles was significantly higher than those of the metal-free macrocycles. To the best of our knowledge, these are the first examples of thermotropic columnar liquid crystals of macrocyclic metal complexes with a large hollow area.

Double helices of a pyridine-appended zinc chlorophyll derivative.

Self-assembled structures formed from a pyridine-appended zinc chlorophyll derivative are reported. While the zinc complex forms cyclic oligomers in chloroform solution, as indicated by (1)H NMR studies (including diffusion-ordered spectroscopy), vapor pressure osmometry, and cold-spray ionization mass spectrometry, it forms double-stranded helical coordination polymers in the solid state, as revealed by single-crystal X-ray analysis.

Design of supramolecular hybrid nanomaterials comprising peptide-based supramolecular nanofibers and in situ generated DNA nanoflowers through rolling circle amplification.

The artificial construction of multicomponent supramolecular materials comprising plural supramolecular architectures that are assembled orthogonally from their constituent molecules has attracted growing attention. Here, we describe the design and development of multicomponent supramolecular materials by combining peptide-based self-assembled fibrous nanostructures with globular DNA nanoflowers constructed by the rolling circle amplification reaction. The orthogonally constructed architectures were dissected by fluorescence imaging using the selective fluorescence staining procedures adapted to this study. The present, unique hybrid materials developed by taking advantage of each supramolecular architecture based on their peptide and DNA functions may offer distinct opportunities to explore their bioapplications as a soft matrix.

Mesogenic discrete metallofoldamer for columnar liquid crystal.

A mesogenic metallofoldamer [(1R,R-Ni)2Pd] exhibits thermotropic columnar liquid crystalline properties. The metallofoldamer was prepared from two homochiral crescent-shaped precursors having ß-diketonate ligands (1R,R-Ni) through bridging by metal complexation; it exhibited a single helicity owing to the overlapping of both ends. The precursor and metallofoldamer formed similar hexagonal columnar phases. The helical metallofoldamer exhibited the hexagonal columnar phase at the higher temperature range owing to its rigid helical mesogenic structure.

Liquid-crystalline Metallomacrocycles Composed of Bis(hydroxypyridono)toluene Ligand and Cu2+ Ions.

A series of π-extended chelating scaffolds incorporating two hydroxypyridone moieties were synthesized. X-ray crystallographic analysis revealed that a bis(hydroxypyridono)toluene ligand possessed a unique π-extended structure and exhibited efficient phase segregation from the aliphatic chains attached at the heterocyclic nitrogen. The bis-bidentate ligand formed a metal-coordination-induced macrocycle with Cu2+ ions. During the complexation, a spectral change in the visible region was induced. Furthermore, the successful development of a liquid crystal of the metallomacrocycle with appropriate side chains was achieved. Examples of liquid-crystalline macrocycles formed via metal-mediated self-assembly are still rare. Among them, the macrocycle described in this paper showed an obvious hexagonal columnar phase reflecting the three-fold symmetric planar structure of the mesogenic metal complex.

Near-infrared absorption by intramolecular charge-transfer transition in 5,10,15,20-tetra(N-carbazolyl)porphyrin through protonation.

A porphyrin coupled quadruply with N-carbazolyl groups at the meso positions has been synthesized. Because of the electron-withdrawing nature of the carbazole units at the porphyrin centre, the tetra(N-carbazolyl)porphyrin and the protonated derivative display unique absorption bands derived from intramolecular charge-transfer transition from the carbazoles to the porphyrin moiety.

Novel host-guest organogels as stabilized by the formation of crown-ammonium pseudo-rotaxane complexes.

A dibenzo-24-crown-8 derivative bearing two cholesterol groups is either insoluble in or precipitates from most organic solvents, but its pseudo-rotaxane complex with a diammonium guest acts as a good gelator of aromatic solvents.

Electron donors and acceptors based on 2,7-functionalized pyrene-4,5,9,10-tetraone.

An efficient synthesis of 2,7-dibromo- and diiodo-pyrene(4,5,8,19)-tetraones led to strong donors and acceptors based on pyrene. They are versatile building blocks for conjugated materials and can be further applied in molecular electronics.

Quater-, quinque-, and sexithiophene organogelators: unique thermochromism and heating-free sol-gel phase transition.

A series of quater-, quinque-, and sexithiophene derivatives bearing two cholesteryl groups at the alpha-position, which are abbreviated as 4 T-(chol)(2), 5 T-(chol)(2), and 6 T-(chol)(2), respectively, have been synthesized. It has been found that these oligothiophene derivatives act as excellent organogelators for various organic fluids and show the unique thermochromic behaviors through the sol-gel phase transition. It was shown on the basis of extensive investigations, performed with UV-visible spectroscopy, circular dichroism (CD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM), that these gelators self-assemble into the one-dimensional structures in the organogels, in which the pi-block moieties of the oligothiophenes are stacked in an H-aggregation mode. Surprisingly, an AFM image shows that 4 T-(chol)(2) forms unimolecular fibers in a left-handed helical sense, whereby one pitch of the helical fiber is constructed by 400-540 4 T-(chol)(2) molecules. Very interestingly, the conformational change in the oligothiophene moieties can be visually detected: for example, 6 T-(chol)(2) shows a specific absorption maximum in the gel (lambda(max) = 389 nm) and in the solution (lambda(max) = 439 nm). In addition, a sol-gel phase transition of the 6 T-(chol)(2) gel was implemented by addition of oxidizing and reducing reagents such as FeCl(3) and ascorbic acid, respectively. The stimuli-responsive functionality of the oligothiophene-based organogels makes them promising candidates for switchable opto- and electronic soft materials.

Creation of a mixed-valence state from one-dimensionally aligned TTF utilizing the self-assembling nature of a low molecular-weight gel.

One-dimensional TTF assemblies have been obtained through the design of low molecular-weight gels, which show a characteristic absorption band at around 1750 nm upon I2 doping, assignable to a mixed-valence state of the TTF assemblies.

A coordination gelator that shows a reversible chromatic change and sol-gel phase-transition behavior upon oxidative/reductive stimuli.

A novel coordination gelator exhibits reversible chromatic and sol-gel phase-transition phenomena triggered by thermal and chemical stimuli.