Gas permeation properties of poly(silamine) membrane

The gas permeation characteristics of poly(silamine) membrane, which consists of alternating 3,3-dimethyl-3-silapentane and N,N′-diethylethylenediamine units in the main chain, were investigated. Though poly(silamine) shows high flexibility (glass transition temperature of −88°C), the gas permeabilities were much lower than those of other rubbery polymers such as poly(dimethylsiloxane) and natural rubber. The activation energies of diffusion in poly(silamine) were much higher than that of natural rubber. On the basis of these results, we propose a model such that the interaction between the Si atom and gas molecules (O₂ and N₂) prevents the free diffusion of the gas molecule in the poly(silamine) membrane. © 1997 John Wiley & Sons, Ltd.     

Self-assembly of oligothiophene chromophores by m-calix[3]amide scaffold

m-Calix[3]amides carrying the bithiophene chromophore (BTC3A) and terthiophene chromophore (TTC3A) were synthesized by the cyclic trimerization of m-aminobenzoic acid esters for the purpose of the control and understanding of the self-assembly of oligothiophene chromophores. Polymers and model compounds were also prepared for comparison. From the (1)H NMR experiments, cyclic trimer BTC3A showed the syn/anti equilibrium in solution, and the syn/anti conformer ratio (76/24 in CDCl(3)) was influenced by the solvent character. Namely, the population of the syn conformer was lowest (70%) in THF-d(8) and was highest (86%) in CDCl(3)/CD(3)OD (1/1 in volume). On the other hand, the population of the syn conformer of cyclic trimer TTC3A was high (84%) even in CDCl(3). In a CHCl(3) solution of cyclic trimer BTC3A, the absorption maximum (342 nm) blue-shifted and the emission maximum (448 nm) red-shifted compared with those of polymer BTPA and model compound BTM. The solvent character also had an impact on the optical properties of cyclic trimer BTC3A. The red-shifted emission maximum (481 nm) of cyclic trimer BTC3A in CH(3)OH indicated the interaction between three bithiophene chromophores. The emission maxima of cyclic trimer TTC3A (486 nm) demonstrated a small red-shift from model compound TTM (477 nm), and no solvent dependency was observed, unlike cyclic trimer BTC3A.     

Two types of two-component gels formed from pseudoenantiomeric ethynylhelicene oligomers

Two-component gels formed from pseudoenantiomeric ethynylhelicene oligomers in toluene exhibited two different properties depending on difference in numbers of helicenes in the two components. The combinations (M)-5/(P)-4, (M)-6/(P)-4, and (M)-7/(P)-4, which contained oligomers with comparable numbers of helicenes, formed transparent gels (Type I gels). The combinations (M)-6/(P)-3, (M)-7/(P)-3, and (M)-8/(P)-3, which contained oligomers with considerably different numbers of helicenes, formed turbid gels (Type II gels). Negative Cotton effects were observed for the Type I gels in the region between 350 and 450 nm, and were positive for the Type II gels, despite the use of (M)-oligomers for the longer components. UV/vis exhibited absorption maxima at 350 nm for the Type I gels and at 338 nm for the Type II gels. Different behaviors in gel formation processes were observed by fluorescence studies. Atomic force microscopy analysis showed fiber structures of 25-50 nm diameter for Type I gels and bundles of 100-150 nm diameter for Type II gels. The stoichiometry in gel formation also differed: The Type I gels showed 1:1 stoichiometry of the two components; the Type II gels showed no 1:1 stoichiometry, likely 1:2 stoichiometry. Using the Type I and II gels, two-layer gel systems were constructed.     

Colloidal crystals of cationic spheres

Colloidal single crystals of cationic polymer spheres (198–250 nm in diameter) in deionized aqueous dispersions were formed for the first time. The spheres used were poly(styrene-co-methacryloyloxyphenyldimethylsulfonium) cations. These cations are unstable in deionized suspensions with mixed beds of cation-exchange and anion-exchange resins. This was clarified by reflection spectroscopy, pH, conductance and -potential measurements for 250 days after suspension preparation. Colloidal crystals formed over a period of 24 h for the deionized suspensions at sphere concentrations higher than 0.09 in volume fraction. The nearest-neighbor intersphere distances coincide satisfactorily with the calculated values using the diameter and the concentration of the spheres. Alloy crystals formed from binary mixtures of the cationic polymer spheres and the anionic silica spheres when the ratio of the volume fraction of cationic spheres against the sum of the both cationic and anionic spheres was smaller than 0.3.     

Densities and Viscosities of Tris(acetylacetonato)cobalt(III) Complex Solutions in Various Solvents

The densities and the viscosities of tris(acetylacetonato)cobalt(III) solutions in acetonitrile, dichloromethane, chloroform, tetrachloromethane, benzene, toluene, ethylbenzene, and p-xylene were measured in the dilute concentration regions at several temperatures ranging from 278 to 313 K under ambient pressure. The partial molar volumes of the solvents and solute were calculated. They are independent of concentration and increase slightly as the temperature increases. The viscosity A- and B-coefficients of the Jones-Dole equation were obtained. The A-coefficients were found to be zero within experimental error. The B-coefficients are positive and decrease as the temperature increases. Thermodynamic quantities of activation for viscous flow were calculated on the basis of Eyring’s viscosity equation. From the quantities obtained in this study, along with some information from the literature, it is suggested that structure-making interactions occur between the segments of the complex and the solvent molecules. These interactions include electrostatic interactions between the local charge on the complex and the dipole moment of the solvent in solutions of acetonitrile and dichloromethane, interlocking packing interactions along C ₃-axis of the complex with solvent in solutions of chloroform and tetrachloromethane, and π-electron interactions between the chelate ring of the complex and the solvent in solutions of benzene, toluene, ethylbenzene, and p-xylene.     

Syntheses of (5E)-PGE2 and New 6-Functionalized Derivatives by the Use of Palladium-Catalyzed Decarboxylative Allylic Alkylation

(5 )-Prostaglandin E₂ (7) was synthesized fron ( )-4- -butyldimethylsilyloxy-2-cyclopentenone (1) by 2-alkenyloxycarbonylatlon of the organocopper conjugate-addition adduct (3) followed by intramolecular palladium-catalyzed decarboxylative allylic alkylation. The (5 )-prostaglandin E₂ skeleton was also obtained from the β-keto allylic ester (11) by a similar decarboxylative allylic alkylation. The decarboxylative allylic alkylation of another type of the three-component coupling product (12) gave new 6-methyleneprostaglandin E1 skeleton (15a), which was converted into new 6-methylprosta-glandin I methyl ester (20) 6-methyleneprostaglandin F₁ derivative (16) by two different ways. The stereochemistry of this intramolecular decarboxylative allylic alkylation was discussed in the reaction of 2-[( )- or ( )-2-butenyloxy-carbonyl] cyclopentanone systems.     

Mechanism of the photochemical ligand substitution reactions of fac-[Re(bpy)(CO)(3)(PR(3))](+) complexes and the properties of their triplet ligand-field excited states

We report herein the mechanism of the photochemical ligand substitution reactions of a series of fac-[Re(X(2)bpy)(CO)(3)(PR(3))](+) complexes (1) and the properties of their triplet ligand-field ((3)LF) excited states. The reason for the photostability of the rhenium complexes [Re(X(2)bpy)(CO)(3)(py)](+) (3) and [Re(X(2)bpy)(CO)(3)Cl] (4) was also investigated. Irradiation of an acetonitrile solution of 1 selectively gave the biscarbonyl complexes cis,trans-[Re(X(2)bpy)(CO)(2)(PR(3))(CH(3)CN)](+) (2). Isotope experiments clearly showed that the CO ligand trans to the PR(3) ligand was selectively substituted. The photochemical reactions proceeded via a dissociative mechanism from the (3)LF excited state. The thermodynamical data for the (3)LF excited states of complexes 1 and the corrective nonradiative decay rate constants for the triplet metal-to-ligand charge-transfer ((3)MLCT) states were obtained from temperature-dependence data for the emission lifetimes and for the quantum yields of the photochemical reactions and the emission. Comparison of 1 with [Re(X(2)bpy)(CO)(3)(py)](+) (3) and [Re(X(2)bpy)(CO)(3)Cl] (4) indicated that the (3)LF states of some 3- and 4-type complexes are probably accessible from the (3)MLCT state even at ambient temperature, but these complexes were stable to irradiation at 365 nm. The photostability of 3 and 4, in contrast to 1, can be explained by differences in the trans effects of the PR(3), py, and Cl(-) ligands.     

Bent Molecules with a 60° Central Core Angle that Form B7 and B2 Phases

Small‐angle bent‐core liquid‐crystalline (LC) molecules based on a 1,2‐bis(phenylethynyl)benzene central core have been synthesized that form banana smectic phases with a ferroelectric B7–antiferroelectric B2 phase sequence upon cooling. The formation of polar, switchable ferro‐/antiferroelectric banana phases indicates that, despite the low core bend angle of approximately 60°, banana smectic phases are still formed with the bend direction parallel to the layer. This study offers significant evidence that shows bent‐core molecules with a 60° bend angle can form the well‐known B2 and B7 banana phases. Consequently, it may lead to the preparation of a wide variety of novel bent molecules with low bend angles that spontaneously form an LC phase with both polarization and chirality.     

Synthesis,Structure, and Properties of α,β‐Linked Oligothiazoles with Controlled Sequence

α,β‐Linked oligothiazoles with head‐to‐tail connectivity are presented as a new family of helical scaffolds. Combinations of palladium‐catalyzed cross‐coupling reactions at the 5‐ and 4‐positions of 2‐phenylthiazole led to the synthesis of oligo(2‐phenylthiazoles) with ortho linkages with a variety of defined sequences. The secondary structures of the α,β‐linked oligo(2‐phenylthiazoles) showed a clear dependence on their sequences. X‐ray crystallography of the trimer, tetramer, and hexamer with head‐to‐tail connection revealed the formation of a helical structure, which was stabilized by a combination of intramolecular forces, including interheteroatom (S???N), CH–π, and π–π interactions. The introduction of a chiral end‐group successfully led to the induction of chirality into the helical conformations. Programmable sequences for controlled geometries and photofunctions have been demonstrated through the manifold connection pathways in α,β‐linked oligothiazoles.     

Giant electric field effect on the second hyperpolarizability of symmetric singlet diradical molecules

This contribution reveals the effects of a static electric field on the static second hyperpolarizability γ of symmetric singlet diradical molecules using the valence configuration interaction scheme. It is found that under the effect of a field, the component of γ along the axis joining the two radical sites can be gigantically (approximately two to three orders) enhanced for symmetric diradicals having intermediate diradical characters with respect to those of closed-shell and pure diradical molecules in the absence of a field. Moreover, this electric field enhancement of γ increases as a function of the diradical character. These results and their analysis propose therefore a new strategy to design materials with exceptional nonlinear optical responses.