Rhodium-Catalyzed [2+1+2+1] Cycloaddition of Benzoic Acids with Diynes through Decarboxylation and C≡C Triple Bond Cleavage

It has been established that an electron-deficient cyclopentadienyl rhodium(III) (Cp^ERh^III) complex catalyzes the oxidative and decarboxylative [2+1+2+1] cycloaddition of benzoic acids with diynes through C≡C triple bond cleavage, leading to fused naphthalenes. This cyclotrimerization is initiated by directed ortho C−H bond cleavage of a benzoic acid, and the subsequent regioselective alkyne insertion and decarboxylation produce a five-membered rhodacycle. The electron-deficient nature of the Cp^ERh^III complex promotes reductive elimination giving a cyclobutadiene–rhodium(I) complex rather than the second intermolecular alkyne insertion. The oxidative addition of the thus generated cyclobutadiene to rhodium(I) (formal C≡C triple bond cleavage) followed by the second intramolecular alkyne insertion and reductive elimination give the corresponding [2+1+2+1] cycloaddition product. The synthetic utility of the present [2+1+2+1] cycloaddition was demonstrated in the facile synthesis of a donor–acceptor [5]helicene and a hemi-hexabenzocoronene by a combination with the chemoselective Scholl reaction.     

Stability of Degenerate Stationary Waves for Viscous Gases

This paper is concerned with the asymptotic stability of degenerate stationary waves for viscous gases in the half space. We discuss the following two cases: (1) viscous conservation laws and (2) damped wave equations with nonlinear convection. In each case, we prove that the solution converges to the corresponding degenerate stationary wave at the rate t ^−α/4 as t → ∞, provided that the initial perturbation is in the weighted space L²_a=L²(\mathbb R₊; (1+x)^a dx){L^2_\alpha=L^2({\mathbb R}_+;\,(1+x)^\alpha dx)} . This convergence rate t ^−α/4 is weaker than the one for the non-degenerate case and requires the restriction α < α_*(q), where α_*(q) is the critical value depending only on the degeneracy exponent q. Such a restriction is reasonable because the corresponding linearized operator for viscous conservation laws cannot be dissipative in L²_a{L^2_\alpha} for α > α^*(q) with another critical value α^*(q). Our stability analysis is based on the space–time weighted energy method in which the spatial weight is chosen as a function of the degenerate stationary wave.     

Optical,Electrochemical, and Magnetic Properties of Pyrrole‐ and Thiophene‐Bridged 5,15‐Diazaporphyrin Dimers

The first examples of pyrrole‐ and thiophene‐bridged 5,15‐diazaporphyrin (DAP) dimers are prepared through Stille coupling reactions of nickel(II) and copper(II) complexes of 3‐bromo‐10,20‐dimesityl‐5,15‐diazaporphyrin (mesityl=2,4,6‐trimethylphenyl) with the respective 2,5‐bis(tributylstannyl)heteroles. The effects of the heterole spacers and meso nitrogen atoms on the optical, electrochemical, and magnetic properties of the DAP dimers are investigated by UV/Vis absorption spectroscopy, density functional theory calculations, magnetic circular dichroism spectroscopy, cyclic voltammetry, and EPR spectroscopy. The heterole spacers are found to have a significant impact on the electronic transitions over the entire π‐system. In particular, the pyrrole‐bridged DAP dimers exhibit high light‐harvesting potential in the low‐energy visible/near‐infrared region owing to the intrinsic charge‐transfer character of the lowest excitation.     

Photostability of the laser dye DCM in various inorganic-organic host matrices

The laser dye, 4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran (DCM) was incorporated in various inorganic-organic host matrices by the sol-gel technique. The photostability of the DCM-doped materials under CW argon laser irradiation was investigated. The absorption of DCM monomer ar 480 nm decreased with increasing irradiation time and was accompanied by an increase in the absorption at 352 nm by inactive photoproducts. Photostability was estimated by measuring the decay rates of DCM fluorescences in different host matrices. The rates exhibited two components; a rapid decay within the first several tens of seconds followed by a slower luminescence decay. The rapid decay depended upon the DCM content in the matrix while the slow decay component was related to the mobility of the DCM in the different matrices. The silica host matrix containing phenyl and a small amount of epoxy groups exhibited the best photostability of the materials examined.     

Creation of magnetic cerasomes through electroless plating and their manipulation using external magnetic fields

Magnetic cerasome, an artificial cell membrane having ultrathin magnetic metal layers on the surface, was prepared through electroless plating of magnetic metal alloy onto an organic–inorganic vesicular nanohybrid “cerasome.” Morphological and functional characteristics of the magnetic cerasome were evaluated using various physical measurements: scanning and transmission electron microscopies, energy-dispersive X-ray spectroscopy, electron tomography, and vibrating sample magnetometry. The results proved that high morphological stability of the cerasome was important for constructing the magnetic lipid vesicle and that insertion of an alkylated metal ligand into the cerasome was essential to the magnetic metal alloy deposition on the cerasome surface. Fluorescence microscopic observations revealed that the magnetic cerasomes were collected reversibly on the slide glass surface and manipulated depending on external motion of a magnet. The potential use of the magnetic cerasomes as a novel vesicular nanohybrid is also described in this report.     

Stereochemical studies of optically active 2-hydroxy-5-alkyl-δ-valerolactone derivatives as chiral dopant for ferroelectric liquid crystals

Both (2S, 5R)- and (2R, 5R)-2-hydroxy-5-alkyl-δ-valerolactone derivatives, cis and trans, respectively, show almost the same magnitude of spontaneous polarization (P_s) when added to a non-chiral smectic C mixture. The stereochemistry of these chiral dopants was studied using ¹H NMR. Trans derivatives seem to have a half-chair conformation with the 2, 5-diequatorial substituents and the cis derivatives have rather a flat conformation in solution. However in the liquid-crystalline phase, the cis and trans derivatives appear to change their conformation or the distribution of their conformations as the alkyl chain length is varied. The difference in the effect as a chiral dopant depends upon lateral interactions between chiral molecules through the solvent liquid crystal phase.