Intramolecular Diels–Alder reaction in enyne–allenes: a computational investigation and comparison with the Myers–Saito and Schmittel reactions

The reaction mechanisms as well as substituted effect and solvent effect of the enyne–allenes are investigated by Density Functional Theory (DFT) method and compared with the Myers–Saito and Schmittel reactions. The Myers–Saito reaction of non‐substituted enyne–allenes is kinetically and thermodynamically favored as compared to the Schmittel reaction; while the concerted [4 + 2] cycloaddition is only 1.32 kcal/mol higher than the C₂? C₇ cyclization and more exothermic (Δ_RE = ?69.38 kcal/mol). For R₁ = CH₃ and t‐Bu, the increasing barrier of the C₂? C₇ cyclization is higher than that for the C₂? C₆ cyclization because of the steric effect, so the increased barrier of the [4 + 2] cycloaddition is affected by such substituted electron‐releasing group. Moreover, the strong steric effect of R₁ = t‐Bu would shift the C₂? C₇ cyclization to the [4 + 2] cycloaddition. On the other hand, for R₁ = Ph, NH₂, O^?, NO₂, and CN substituents, the barrier of the C₂? C₆ cyclization would be more diminished than the C₂? C₇ cyclization due to strong mesomeric effect; the reaction path of C₂? C₇ cyclization would also shift to the [4 + 2] cycloaddition. The solvation does not lead to significant changes in the potential‐energy surface of the reaction except for the more polar surrounding solvent such as dimethyl sulfoxide (DMSO), or water. Copyright © 2009 John Wiley & Sons, Ltd.     

The influence of indium on the structural modification of the amorphous Ge–In–Se system

The effect of both the chemical composition and the nature of the chemical bonding of amorphous alloyed samples of Ge_xIn_ySe_100−x−y prepared under vacuum with x=20, 4y15 on the efficiency of the structural modification Δφ is analysed using a simple consideration based on the coordination number Z, and the number of topological constraints N_co. The previously obtained parameters have been used for the determination of the number of continuous deformation (i.e. zero-frequency modes f ), and for the estimation of the cohesive energies of these glasses, assuming simple additivity of bond energies. A trial has been made to correlate the results of this paper with the previously published data of glass transition temperature T_g, activation energy ₀ and the shift of the K-absorption edge (ΔE_K) of the composition of vacuum prepared Ge_xIn_ySe_100−x−y. It was found that there is a correlation between the lone-pair electrons and the stability of the vitreous state. According to the criterion of Liang, the above correlation has been interpreted in terms of Δφ.     

Review of the Theoretical Description of Time‐Resolved Angle‐Resolved Photoemission Spectroscopy in Electron‐Phonon Mediated Superconductors

We review recent work on the theory for pump/probe photoemission spectroscopy of electron‐phonon mediated superconductors in both the normal and the superconducting states. We describe the formal developments that allow one to solve the Migdal‐Eliashberg theory in nonequilibrium for an ultrashort laser pumping field, and explore the solutions which illustrate the relaxation as energy is transferred from electrons to phonons. We focus on exact results emanating from sum rules and approximate numerical results which describe rules of thumb for relaxation processes. In addition, in the superconducting state, we describe how Anderson‐Higgs oscillations can be excited due to the nonlinear coupling with the electric field and describe mechanisms where pumping the system enhances superconductivity.     

Self‐association,tautomerism and E–Z isomerization of isatin–phenylsemicarbazones – spectral study and theoretical calculations

The self‐association and tautomerism of (E)‐isatin‐3‐4‐phenyl(semicarbazone) Ia and (E)‐N‐methylisatin‐3‐4‐phenyl(semicarbazone) IIa were investigated in solvents of various polarity. In weakly interacting non‐polar solvents, such as CHCl₃ and benzene, phenylsemicarbazone concentrations above 1×10^?5 mol dm^?3 result in the formation of dimers or higher aggregates of E‐isomers Ia and IIa . This aggregate formation prevents room temperature E–Z isomerization of Ia and IIa to more stable Z‐isomers. In contrast to the situation in non‐polar solvents, E–Z isomerization from the monomeric form of phenylsemicarbazone Ia and IIa E‐isomers occurs in highly interactive polar solvents including MeOH and DMF only at temperatures above 70 °C. Moreover, decrease in phenylsemicarbazone concentration below 1×10^?4 mol dm^?3 in these highly solute–solvent interacting systems leads to aggregate dissociation, and a new hydrazonol tautomeric form with a high degree of conjugation predominates in these solutions. Theoretical calculations confirm obtained experimental results. Copyright © 2013 John Wiley & Sons, Ltd.     

Photostability of D–π–A nonlinear optical chromophores containing a benzothiazolium acceptor

For the practical application of second‐order NLO materials, not only a high molecular quadratic hyperpolarizability β but also good thermal, chemical, and photochemical stabilities are required. Most of the state‐of‐the‐art chromophores with high NLO response cannot be put to use because they are photochemically highly unstable. Good thermal and photochemical stabilities with preserved high hyperpolarizabilities can be achieved by replacement of an aromatic ring with easily delocalizable heteroaromatics, e.g., with benzothiazole. Furthermore, desirable modifications of the benzothiazole fragment lead to improvement in β values. Here we report results of a comprehensive investigation of the photochemical stability of seven D–π–A push–pull molecules based on a N‐methylbenzothiazolium acceptor and a N,N‐dimethylaminophenyl donor with a different length of conjugated bridge and different acceptor strength. The quantum yield (Φ) and the kinetic parameters of photoreactions were determined for existing photodegradation pathways on irradiation at 300–850 nm in MeOH. Trans–cis photoisomerization is proposed as a fast but inefficient photobleaching mechanism for these irradiation wavelengths. Self‐sensitized photooxidation by ¹O₂ makes very slow parallel photodegradation pathway and, albeit to small value of Φ, plays a dominant role in the photodegradation of the compounds investigated. Both structural modifications (extension of conjugated bridge and an additional acceptor group bonded to heterocycle) resulting in an increase of NLO response led to a decrease in photostability due to the self‐sensitized ¹O₂ photooxidative attack. Thus a compromise should be found between an increase in NLO response and a decrease in photostability to make a choice of studied compounds for practical applications. Copyright © 2010 John Wiley & Sons, Ltd.     

Consolidation of hydrogenation–disproportionation–desorption–recombination processed Nd–Fe–B magnets by spark plasma sintering

We have successfully consolidated hydrogenation–disproportionation–desorption–recombination (HDDR) processed Nd–Fe–Co–Zr–B–Ga powder by spark plasma sintering (SPS). The field compacted samples were sintered at different temperatures (T_S) from 550 to 600 °C with compressive pressure of 80 MPa for 20 min. Microstructural investigations by transmission electron microscopy indicated that the sintered specimen exhibits Nd₂Fe₁₄B grains of ~300 nm with Nd-rich grain boundary phase. The optimum magnetic properties of B_r: 1.22 T, H_c: 928 kA/m, _BH_c: 600 kA/m, (BH)_max: 210 kJ/m³ were obtained in the sample sintered at 550 °C. The strategy for further improving the coercivity and remanence is discussed based on the microstructure-property relationships.     

A new form of the Sutton–Chen potential for the Cu–Ag alloys

The analytic construction of a many-body potential inspired from the Sutton–Chen parametrization is presented for copper and silver. A new approach is used to model the cross interaction for the Cu–Ag alloys. The parameters are fitted to first principles calculations based on the full potential linear plane wave method. The structural properties of the order and disorder Cu–Ag alloys in the B₂and fcc structures are presented for different concentration.     

Interface-charged impurity scattering in semiconductor MOSFETs and MODFETs: temperature-dependent resistivity and 2D ‘metallic‘ behavior

We present the results on the anomalous 2D transport behavior by employing Drude–Boltzmann transport theory and taking into account the realistic charge impurity scattering effects. Our results show quantitative agreement with the existing experimental data in several different systems and address the origin of the strong and nonmonotonic temperature-dependent resistivity.     

Visible to NIR absorbing C–N and C–C bonding squaraines: A computational study

We report a comparative computational study of 2 series of molecules with C–N bonding squaraines (NSQ) and C–C bonding squaraines (CSQ), having absorption from visible to near infrared region (350‐800 nm). The NSQ are considered as molecules with break‐in conjugation, and CSQ are considered as molecules with complete conjugation in molecular backbone. The lowest electronic excitations in CSQ molecules are always having around 200 nm red shifted absorption than its corresponding NSQ molecules. The reason for this drastic red shift in CSQ series than NSQ has been systematically studied by density functional theory, time‐dependent density functional theory, and symmetry adopted cluster configuration interaction methods. The CSQ series are showing less charge transfer than NSQ, but having small diradical character. This study may be helpful in design and synthesis of new squaraine dyes, which are useful in materials applications.     

Vectorial structure of Hermite–Laguerre–Gaussian beam in the far field

Starting from Maxwell's equations, a Hermite–Laguerre–Gaussian (HLG) beam is decomposed into the TE and TM terms by using the vector angular spectrum representation. By means of the method of stationary phase, the analytical TE and TM terms are presented in the far field. The energy flux distributions of the TE and TM terms are also investigated and depicted in the far field. The influences of the additional angle parameter and Gaussian waist width on the vectorial structure and energy flux pattern of HLG beam are also investigated. This research reveals the internal vectorial structure of HLG beam and may provide a new approach to the manipulation of laser beams.     

A continuation BSOR-Lanczos–Galerkin method for positive bound states of a multi-component Bose–Einstein condensate

We develop a continuation block successive over-relaxation (BSOR)-Lanczos–Galerkin method for the computation of positive bound states of time-independent, coupled Gross–Pitaevskii equations (CGPEs) which describe a multi-component Bose–Einstein condensate (BEC). A discretization of the CGPEs leads to a nonlinear algebraic eigenvalue problem (NAEP). The solution curve with respect to some parameter of the NAEP is then followed by the proposed method. For a single-component BEC, we prove that there exists a unique global minimizer (the ground state) which is represented by an ordinary differential equation with the initial value. For a multi-component BEC, we prove that m identical ground/bound states will bifurcate into m different ground/bound states at a finite repulsive inter-component scattering length. Numerical results show that various positive bound states of a two/three-component BEC are solved efficiently and reliably by the continuation BSOR-Lanczos–Galerkin method.     

Adamantyl‐endcapped polyynes

Polyynes spanning from a diyne to a dodecayne with adamantyl endgroups have been synthesized using the Fritsch–Buttenberg–Wiechell rearrangement as a key step to construct the acetylenic framework. Molecular properties as a function of polyyne length have been analyzed by UV–Vis spectroscopy, cyclic voltammetry, differential scanning calorimetry, and X‐ray crystallography. Copyright © 2011 John Wiley & Sons, Ltd.     

Dihydrogen bond and X–H…σ interaction as sub‐classes of hydrogen bond

Dihydrogen bond (DHB) and X–H…σ interaction are discussed and compared here. Both interactions possess numerous characteristics of the hydrogen bond (HB). The Natural Bond Orbitals method results show that σ → σ* is the most important interaction connected with the electron charge transfer from the Lewis base to the Lewis acid for the DHB as well as for the X–H…σ HB. However, there are distinct differences between these interactions, and this is evident from the analysis based on the Quantum Theory of Atoms in Molecules as well as from the decomposition of the energy of interaction. The X–H…π interaction is also discussed here since it possesses few characteristics typical for the X–H…σ interaction and not for the DHB. Copyright © 2013 John Wiley & Sons, Ltd.     

Towards Drinfeld–Sokolov reduction for quantum groups

In this paper we study the Poisson–Lie version of the Drinfeld–Sokolov reduction defined in [E. Frenkel, N. Reshetikhin, M.A. Semenov-Tian-Shansky, Drinfeld–Sokolov reduction for difference operators and deformations of W-algebras. I. The case of Virasoro algebra, Comm. Math. Phys. 192 (1998) 605; M.A. Semenov-Tian-Shansky, A.V. Sevostyanov, Drinfeld–Sokolov reduction for difference operators and deformations of W-algebras. II. General semisimple case, Comm. Math. Phys. 192 (1998) 631]. Using the bialgebra structure related to the new Drinfeld realization of affine quantum groups we describe reduction in terms of constraints. This realization of reduction admits direct quantization.As a byproduct we obtain an explicit expression for the symplectic form associated to the twisted Heisenberg double and calculate the moment map for the twisted dressing action. For some class of infinite-dimensional Poisson–Lie groups we also prove an analogue of the Ginzburg–Weinstein isomorphism.     

Dynamics of One‐Dimensional Electrons With Broken Spin–Charge Separation

Spin–charge separation is known to be broken in many physically interesting one‐dimensional (1D) and quasi‐1D systems with spin–orbit interaction because of which spin and charge degrees of freedom are mixed in collective excitations. Mixed spin–charge modes carry an electric charge and therefore can be investigated by electrical means. We explore this possibility by studying the dynamic conductance of a 1D electron system with image‐potential‐induced spin–orbit interaction. The real part of the admittance reveals an oscillatory behavior versus frequency that reflects the collective excitation resonances for both modes at their respective transit frequencies. By analyzing the frequency dependence of the conductance the mode velocities can be found and their spin–charge structure can be determined quantitatively.     

Robust Preparation of Atomic Concatenated Greenberger–Horne–Zeilinger States via Shortcuts to Adiabaticity

Here, a protocol for robust preparation of an atomic concatenated Greenberger–Horne–Zeilinger (C‐GHZ) state via shortcuts to adiabaticity (STA) is proposed. The devices for implementing the protocol consist of atoms, cavities, and the optical fibers, which are feasible with current technology. The atoms are trapped in the separated cavities allowing individual control over each atom with classical fields. STA helps to design Rabi frequencies of classical fields so that the atoms can be driven from the initial states to the target states. The numerical simulations show that the protocol holds robustness against atomic spontaneous emissions and photonic leakages. Thus, the protocol may be realized by experiments in the near future.