Chiral helicenoid diarylethene with large change in specific optical rotation by photochromism

A diarylethene possessing one [4]thiaheterohelicene and one benzothiophene, the latter with a chiral methoxymethoxyethyl group on its C-3 position, was proved to work as a switch of specific optical rotation at a wavelength at which both colored and colorless forms have no absorption in solution. The difference of the specific optical rotation was 1300 degrees between the open form and the photostationary state. The specific optical rotation of one of the isolated optically active major colored forms was -4680 degrees. The conversion to the colored form was 64%, and the diastereomeric excess of photocyclization was 47%.     

Terahertz time-domain spectroscopy of imidazolium ionic liquids

We have measured the terahertz (THz) complex dielectric spectra of imidazolium ionic liquids by THz time-domain spectroscopy (THz-TDS) in the frequency range from 5 (0.15 THz) to 140 cm(-1) (4.2 THz). The ionic liquids investigated are 1-ethyl-3-methylimidazolium (EMIm+)/trifluoromethanesulfonate (TfO-), EMIm+/tetrafluoroborate (BF(4)-), 1-butyl-3-methylimidazolium (BMIm+)/TfO-, and BMIm+/BF(4)-. The dielectric values of the ionic liquids in the THz region are similar to those of short-chain alcohols. The THz dielectric values are related to subpicosecond-to-picosecond dynamics. The same trend has been observed in the empirical polarity ET(30) although it is related to the static characteristics of polarity and hydrogen bonding ability. A difference between the two types of liquids is observed in the THz dielectric spectral shapes: the ionic liquids show structured lineshapes but short-chain alcohols show much less structured ones. The structured lineshapes of the ionic liquids reflect the low-frequency motions of interion and/or intramolecular vibrations. When the ionic liquids composed of the different imidazolium cations contain the same anions as counterions, their density-normalized THz dielectric spectra above 20 cm(-1) bear strong resemblance to each other in shape and magnitude. It shows clearly that the THz spectra do not originate from the intramolecular vibrations of the imodazolium cations. All of the intramolecular vibrations of the anions are located above 140 cm(-1) except the CF3-SO3 torsion of TfO-, the band of which alone cannot explain the broad THz dielectric spectra of the ionic liquids. Therefore, we conclude that the interion vibrations rather than the intramolecular vibrations dominantly contribute to the THz dielectric spectra. The results strongly indicate that even in the liquid phase the ionic liquids have local structures similar to their solid-phase structures.     

Excited-state geometries and vibrational frequencies studied using the analytical energy gradients of the direct symmetry-adapted cluster-configuration interaction method. I. HAX-type molecules

In this series of studies, we systematically apply the analytical energy gradients of the direct symmetry-adapted cluster-configuration interaction singles and doubles nonvariational method to calculate the equilibrium geometries and vibrational frequencies of excited and ionized states of molecules. The harmonic vibrational frequencies were calculated using the second derivatives numerically computed from the analytical first derivatives and the anharmonicity was evaluated from the three-dimensional potential energy surfaces around the local minima. In this paper, the method is applied to the low-lying valence singlet and triplet excited states of HAX-type molecules, HCF, HCCl, HSiF, HSiCl, HNO, HPO, and their deuterium isotopomers. The vibrational level emission spectra of HSiF and DSiF and absorption spectra of HSiCl and DSiCl were also simulated within the Franck-Condon approximation and agree well with the experimental spectra. The results show that the present method is useful and reliable for calculating these quantities and spectra. The change in geometry in the excited states was qualitatively interpreted in the light of the electrostatic force theory. The effect of perturbation selection with the localized molecular orbitals on the geometrical parameters and harmonic vibrational frequencies is also discussed.     

Enantioselective decarboxylative alkylation reactions: catalyst development, substrate scope, and mechanistic studies

α-Quaternary ketones are accessed through novel enantioselective alkylations of allyl and propargyl electrophiles by unstabilized prochiral enolate nucleophiles in the presence of palladium complexes with various phosphinooxazoline (PHOX) ligands. Excellent yields and high enantiomeric excesses are obtained from three classes of enolate precursor: enol carbonates, enol silanes, and racemic β-ketoesters. Each of these substrate classes functions with nearly identical efficiency in terms of yield and enantioselectivity. Catalyst discovery and development, the optimization of reaction conditions, the exploration of reaction scope, and applications in target-directed synthesis are reported. Experimental observations suggest that these alkylation reactions occur through an unusual inner-sphere mechanism involving binding of the prochiral enolate nucleophile directly to the palladium center.     

Fabrication of a mid-IR wire-grid polarizer by direct imprinting on chalcogenide glass

A mid-IR wire-grid polarizer with a 500 nm pitch was fabricated on a low toxic chalcogenide glass (Sb-Ge-Sn-S system) by the thermal imprinting of periodic grating followed by the thermal evaporation of Al metal. After imprinting, deposition of Al on the grating at an oblique angle produced a wire-grid polarizer. The fabricated polarizer showed polarization with TM transmittance greater than 60% at 5-9 μm wavelengths and an extinction ratio greater than 20 dB at 3.5-11 μm wavelengths. This polarizer with a high extinction ratio can be fabricated more simply and less expensively than conventional IR polarizers.     

Molecular surface structure of comb-like polyoxyethylene with alkyl sulfonyl side-chains studied by sum-frequency generation vibrational spectroscopy

The orientation of alkyl sulfonyl side-chains on a series of polyoxyethylenes, CH₃–nSE (n?=?6, 8 or 10), and the effect of annealing and rubbing on the molecular orientation of the alkyl side-chains at the substrate surface, were investigated using sum-frequency generation (SFG) vibrational spectroscopy. Based on the SFG spectra and their quantitative interpretation, we deduced that the alkyl chains of CH₃–10SE are almost vertically oriented at the surface and that the terminal methyl groups of the alkyl chains are tilted from the surface normal as much as θ ≈ 40?±?5°, with a broad distribution of tilt angles. We also found that rubbing treatment induced the anisotropic orientation of the alkyl side-chains perpendicular to the rubbing direction, but their orientation was unchanged by annealing.     

Subdiffusive dynamics of a liquid crystal in the isotropic phase

The isotropic phase dynamics of a system of 4-n-hexyl-4'-cyano-biphenyl (6CB) molecules has been studied by molecular dynamics computer simulations. We have explored the range of 275-330 K keeping the system isotropic, although supercooled under its nematic transition temperature. The weak rototranslational coupling allowed us to separately evaluate translational (TDOF) and orientational degrees of freedom (ODOF). Evidences of subdiffusive dynamics, more apparent at the lowest temperatures, are found in translational and orientational dynamics. Mean square displacement as well as self-intermediate center of mass and rotational scattering functions show a plateau, also visible in the orientational correlation function. According to the mode coupling theory (MCT), this plateau is the signature of the beta-relaxation regime. Three-time intermediate scattering functions reveal that the plateau is related to a homogeneous dynamics, more extended in time for the orientational degrees of freedom (up to 1 ns). The time-temperature superposition principle and the factorization property predicted by the idealized version of MCT hold, again for both kinds of dynamics. The temperature dependence of diffusion coefficient and orientational relaxation time is well described by a power law. Critical temperatures Tc are 244+/-6 and 258+/-6 K, respectively, the latter is some 10 K below the corresponding experimental values. The different values of Tc we obtained indicate that ODOF freezes earlier than TDOF. This appears due to the strongly anisotropic environment that surrounds a 6CB molecule, even in the isotropic phase. The lifetime of these "cages," estimated by time dependent conditional probability functions, is strongly temperature dependent, ranging from some hundreds of picoseconds at 320 K to a few nanoseconds at 275 K.     

Spectral estimates for unreduced symmetric KKT systems arising from Interior Point methods

We consider symmetrized Karush–Kuhn–Tucker systems arising in the solution of convex quadratic programming problems in standard form by Interior Point methods. Their coefficient matrices usually have 3 × 3 block structure, and under suitable conditions on both the quadratic programming problem and the solution, they are nonsingular in the limit. We present new spectral estimates for these matrices: the new bounds are established for the unpreconditioned matrices and for the matrices preconditioned by symmetric positive definite augmented preconditioners. Some of the obtained results complete the analysis recently given by Greif, Moulding, and Orban in [SIAM J. Optim., 24 (2014), pp. 49‐83]. The sharpness of the new estimates is illustrated by numerical experiments. Copyright © 2016 John Wiley & Sons, Ltd.     

Enhanced fluorescence detection of metal ions using light-harvesting mesoporous organosilica

Enhanced fluorescence detection of metal ions was realized in a system consisting of a fluorescent 2,2′‐bipyridine (BPy) receptor and light‐harvesting periodic mesoporous organosilica (PMO). The fluorescent BPy receptor with two silyl groups was synthesized and covalently attached to the pore walls of biphenyl (Bp)‐bridged PMO powder. The fluorescence intensity from the BPy receptor was significantly enhanced by the light‐harvesting property of Bp‐PMO, that is, the energy funneling into the BPy receptor from a large number of Bp groups in the PMO framework which absorbed UV light effectively. The enhanced emission of the BPy receptor was quenched upon the addition of a low concentration of Cu²⁺ (0.15–1.2×10^?6 M ), resulting in the sensitive detection of Cu²⁺. Upon titration of Zn²⁺ (0.3–6.0×10^?6 M ), the fluorescence excitation spectrum was systematically changed with an isosbestic point at 375 nm through 1:1 complexation of BPy and Zn²⁺ similar to that observed in BPy‐based solutions, indicating almost complete preservation of the binding property of the BPy receptor despite covalent fixing on the solid surface. These results demonstrate that light‐harvesting PMOs have great potential as supporting materials for enhanced fluorescence chemosensors.