Takeo Sasaki

Dramatic Improvement in Catalyst Loadings and Molar Ratios of Coupling Partners for Ni/Cr-Mediated Coupling Reactions: Heterobimetallic Catalysts

Two new ligands 1a,b are reported. Upon treatment with 1 equiv of NiCl(2) x (MeOCH(2))(2), 1a,b give the corresponding Ni complexes. X-ray analysis of 1a x NiCl(2) established that the NiCl(2) is selectively coordinated to the phenanthroline nitrogens. Ni/Cr heterobimetallic catalysts 1a,b x CrCl(2)/NiCl(2), prepared from 1a,b x NiCl(2), have been shown to behave exceptionally well in catalytic asymmetric Ni/Cr-mediated couplings, with highlights including the following: (1) 1-2 mol % catalyst is sufficient to complete the coupling; (2) only negligible amounts of the dimers, byproducts formed through the alkenyl Ni species, are observed; (3) the coupling goes to completion even with a 1:1 molar ratio of the coupling partners; and (4) the asymmetric induction is practically identical with that obtained from the coupling with the Cr catalysts prepared from (S)-sulfonamides 2a,b. The scope of the new Ni/Cr heterobimetallic catalysts was briefly studied using four additional aldehydes. The applicability of the new catalysts to polyfunctional substrates was demonstrated by two C-C bond formations chosen from the halichondrin/E7389 synthesis as examples.

New Syntheses of E7389 C14−C35 and Halichondrin C14−C38 Building Blocks: Reductive Cyclization and Oxy-Michael Cyclization Approaches

Cr-mediated coupling reactions are usually achieved with a slight excess of a given nucleophile. To develop a cost-effective use of this process, two different approaches have been studied. The first approach depends on two consecutive catalytic asymmetric Cr-mediated couplings, with use of coupling partners purposely being of unbalanced molecular size and complexity. The second approach rests on the success in identifying the nucleophile, which allows us to achieve the coupling satisfactorily with a 1:1 molar ratio of the coupling partners. The C23-O bond is stereospecifically constructed via reductive cyclization of the oxonium ion, or oxy-Michael cyclization. Both syntheses have a high overall efficiency: E7389 C14-C35 and halichondrin C14-C38 building blocks have been synthesized from the corresponding C27-C35 and C27-C38 aldehydes, respectively, in high overall yields with an excellent stereoselectivity. Because of operational simplicity, the synthesis outlined herein appears to be well suited for scaling.

Real-time dynamic hologram in photorefractive ferroelectric liquid crystal with two-beam coupling gain coefficient of over 800 cm–1 and response time of 8 ms

The photorefractive effect in photoconductive ferroelectric liquid crystals (FLCs) that contain photoconductive chiral compounds was investigated. Terthiophene compounds with chiral structure were chosen as the photoconductive chiral compounds and mixed with an achiral smectic C liquid crystal. The mixture exhibited the ferroelectric chiral smectic C phase and photoconductivity. The photorefractivity of the mixture was investigated by two-beam coupling experiment. It was found that the FLC containing the photoconductive chiral compound exhibits a large gain coefficient of over 800 cm−1 and a fast response time of 8 ms. The high photorefractive performance was considered to be due to enhanced charge mobility.

Atomic and electronic structures of Cu/α-Al2O3 interfaces prepared by pulsed-laser deposition

Abstract Interfacial atomic structures of Cu/Al2O3(0001) and Cu/Al2O3 systems prepared by a pulsed-laser deposition technique have been characterized by using high-resolution transmission electron microscopy (HRTEM). It was found that Cu metals were epitaxially oriented to the surface of Al2O3 substrates, and the following orientation relationships (ORs) were found to be formed: (111)Cu⁄⁄(0001)Al2O3, cu⁄⁄Al2O3 in the Cu/Al2O3(0001) interface and (001)Cu⁄⁄Al2O3, Cu⁄⁄[0001]Al2O3 in the Cu/Al2O3 interface. Geometrical coherency of the Cu/Al2O3 system has been evaluated by the coincidence of reciprocal lattice points method, and the result showed that the most coherent ORs were (111)Cu⁄⁄(0001)Al2O3, Cu⁄⁄[11Ī00]Al2O3 and Cu⁄⁄Al2O3, [111]Cu⁄⁄[0001]Al2O3, which are equivalent to each other. These ORs were not consistent with the experimentally observed ORs, and it was possible that crucial factors to determine the ORs between Cu and Al2O3 were not only geometrical coherency, but also other factors such as chemical bonding states. Therefore, to understand the nature of the interface atomic structures, the electronic structures of the Cu/Al2O3 interfaces have been investigated by electron energy-loss spectroscopy. It was found that the pre-edge at the lower energy part of the main peak appeared in the O-K edge spectra at the interface region in both the Cu/Al2O3(0001) and Cu/Al2O3 systems. This indicates the existence of Cu—O interactions at the interface. In fact, HRTEM simulation images based on O-terminated interface models agreed well with the experimental images, indicating that O-terminated interfaces were formed in both systems. Since the overlapped Cu atomic density in the experimental ORs were larger than that in the most coherent OR, it is considered that the on-top Cu—O bonds stabilize the O-terminated Cu/Al2O3 interfaces.

Photochemical switching of polarization in ferroelectric liquid crystals: Effect of structure of host FLCs

Abstract A novel principle for photochemical control of optical properties of ferroelectric liquid crystal (FLC) is presented, which is based on photochemically induced switching of polarization of FLC triggered by photoisomerization of azobenzene derivative doped in FLC. At the irradiated sites of the azobenzene/FLC mixtures, flip of polarization was induced, causing the change of the optical properties. The effects of the structures of host FLCs on the photochemical flip of polarization are discussed.

Photochemical phase transition behaviors of ternary mixtures of photochromic azobenzene derivative, low molecular weight liquid crystal and polymer liquid crystal

Abstract Ternary mixtures of a photochromic azobenzene guest, low molecular weight liquid crystal (LMWLC) and polymer liquid crystal (PLC) were used and their photochemical phase transition behaviors were explored with special Reference to the stability of the photochemically induced isotropic phase and the response to photoirradiation. It was found that the rate of the photochemical phase transition increased as the mole fraction of the LMWLC component increased, demonstrating that the response of the systems is improved in the presence of the LMWLC components. Furthermore, the stability of the photochemically stored image has been shown to be much improved in the presence of the PLC components. Results obtained in this study clearly indicate that the LMWLC/PLC mixtures are promising as hosts for the optical image recording devices.

Liquid crystal photonics : optical switching and image storage by means of nematic liquid crystals and ferroelectric liquid crystals

Optical switching and image storage have been examined by means of liquid crystals (LCs), nematic LCs and ferroelectric LCs. Photochromic molecules were incorporated either by dispersion into host LCs or covalently attached to polymer main chains. These photochromic moieties act as a photoresponsive switch which induces phase transition and change in orientation of LCs, resulting in optical switching and image storage.

Time-Resolved Observation of Isothermal Phase Transition of Liquid Crystals Induced by Photoisomerization of Azobenzene Dopant

Abstract The isothermal phase transition behavior of azobenzene guest/liquid crystal host mixtures induced by nanosecond laser palse was investigated. Two kinds of azobenzene derivatives were employed as dopant, 4-butyl-4′-methoxyazobenzene (BMAB) and 4-hydroxyazobenzene (HOAB), in order to examine the heat effect on the phase transition. BMAB showed a trans to cis photoisomerization while HOAB showed little isomerization even by prolonged photoirradiation. In the BMAB/5CB mixture, the photochemical nematic (N) → isotropic (I) phase transition was found to be completed within ∼ 100 ms at the reduced temperature of 0.998 on irradiation of a single laser pulse of 10 ns FWHM which gave the cis isomer of BMAB. Contrary to the BMAB/5CB mixtare, no phase transition of the HOAB/5CB mixture was observed by the laser flash, indicating that the N-I phase transition observed for the BMAB/5CB mixture is ascribed to the photochemical reaction of the dopant, not to the heat-mode process. The photochemical phase transit...

Formation of dynamic holograms based on spatial modulation of molecular motions of ferroelectric liquid crystals

The formation of dynamic holograms based on the spatial modulation of the molecular motions of ferroelectric liquid crystals (FLCs) was demonstrated. The consecutive rotational switching motion of FLC molecules under an alternating electric field was modulated by the photoinduced additional electric field built at the interference fringe. This spatially periodic difference in molecular motions of an FLC was confirmed to work as a diffraction grating. Since the motion-mode hologram is stable and the response is very fast when compared to photorefractive polymers, the motion-mode hologram appears to be promising for various photonic applications.

Photoreactivity and emission properties of liquid-crystalline twin dimers containing cinnamic acid moieties at both ends of ethylene glycol spacers. I. Synthesis, thermotropic properties and photoreactivity

Abstract Twin dimers containing 4-methoxycinnamic acid moieties at both ends of various lengths of ethylene glycol spacers (nEGMC) were found to exhibit liquid-crystalline phase behaviour, while those with cinnamic acid moieties (nEGC) at both ends did not show the liquid-crystalline phase behaviour. The liquid-crystalline phase behaviour of nEGMC depended on the length of the ethylene glycol spacers, n. Photoirradiation of nEGMC at >300nm resulted in the formation of photodimers through cyclobutane ring formation at the C=C part of the 4-methoxycinnamic acid moieties. The photoreaction was explored by following a decrease in vC=C (FTIR), formation of the photodimers (GPC) and structural analysis of the photoproducts (NMR). It was found that the morphology of the systems strongly affected the photoreactivity and the head-to-head photodimer was predominantly formed. The photoreactivity of nEGMC is discussed in relation to the morphology of the systems.