OPE molecular junction as a hydrogen gas sensor

Oligo(phenylene ethynylene) (OPE) molecular junction has been suggested as a H₂ molecule sensor based on calculations using the first principles of density–functional theory and non-equilibrium Green's function. The electronic transport properties of the OPE molecule between two Au electrodes with or without adsorbed H₂ molecules are investigated. Results show that the adsorbed H₂ molecule significantly changes the characteristics of the current–voltage curve of the OPE molecular junction. The pure OPE molecular junction exhibits a significant negative differential resistance, but this kind of phenomenon will disappear or weaken after hydrogen molecules are adsorbed. The conductance of the junction also obviously decreases in the bias range of [−0.4, 0.4] V after adsorbing H₂ molecules. These effects can be used to design a H₂ molecule sensor.     

(CH3)2和(NH2)2基团修饰的齐聚苯乙炔分子电子输运性质研究

采用密度泛函理论和非平衡格林函数相结合的方法研究了S原子作为单、双端基的(CH₃)₂-OPE (齐聚苯乙炔)和(NH₂)₂-OPE分子在金电极间的电子输运性质. 通过第一性原理优化计算获得分子部分稳定结构, 再置于Au电极之间构成两极系统, 然后再优化整个两极系统获得稳定结构. 另外, 通过非平衡格林函数方法计算了两极系统的电子输运性质. 计算结果表明, 不同的修饰基团和桥接方式可以导致两极系统的开关效应、负微分电阻行为和整流行为等不同的电子输运性质. 通过计算不同偏压下的分子体系投影轨道电子分布、透射谱、态密度, 对这些新异的电输运性质出现的机理进行了解释.     

Role of highest occupied molecular orbitals in molecular field-free alignment by a femtosecond pulse

This paper studies the molecular rotational excitation and field-free spatial alignment in a nonresonant intense laser field numerically and analytically by using the time-dependent Schr?dinger equation. The broad rotational wave packets excited by the femtosecond pulse are defined in conjugate angle space, and their coefficients are obtained by solving a set of coupled linear equations. Both single molecule orientation angles and an ensemble of O₂ and CO molecule angular distributions are calculated in detail. The numerical results show that, for single molecule highest occupied molecular orbital (HOMO) symmetry σ tends to have a molecular orientation along the laser polarization direction and the permanent dipole moment diminishes the mean of the orientation angles; for an ensemble of molecules, angular distributions provide more complex and additional information at times where there are no revivals in the single molecule plot. In particular, at the revival peak instant, with the increase of temperature of the molecular ensemble, the anisotropic angular distributions with respect to the laser polarization direction of the π _g orbital gradually transform to the symmetrical distributions regarding the laser polarization vector and for two HOMO configurations angular distributions of all directions are confined within a smaller angle when the temperature of the molecular ensemble is higher.     

0D–2D and 1D–2D Semiconductor Hybrids Composed of All Inorganic Perovskite Nanocrystals and Single‐Layer Graphene with Improved Light Harvesting

In this study, inorganic cesium lead iodide (CsPbI₃) perovskite nanoparticles (PNPs) and perovskite nanowires (PNWs) with single‐layer graphene (SLG) are combined to obtain 0D–2D PNP–SLG and 1D–2D PNW–SLG hybrids with improved light harvesting. Time‐resolved single‐nanostructure photoluminescence studies of PNPs, PNWs, and related hybrids reveal (i) quasi‐two‐state photoluminescence blinking in PNPs, (ii) highly polarized photoluminescence emitted by PNWs and (iii) efficient interfacial electron transfer between perovskite nanostructures and SLG in both PNP–SLG and PNW–SLG hybrids. Doping of poorly absorbing, highly conductive SLG with perovskite nanocrystals and nanowires provides a simple, yet efficient path to obtain hybrids with increased light‐harvesting properties for potential utilization in the next‐generation photodetectors and photovoltaic devices, including polarization sensitive photodetectors.     

DESIRS: a state‐of‐the‐art VUV beamline featuring high resolution and variable polarization for spectroscopy and dichroism at SOLEIL

DESIRS is a new undulator‐based VUV beamline on the 2.75 GeV storage ring SOLEIL (France) optimized for gas‐phase studies of molecular and electronic structures, reactivity and polarization‐dependent photodynamics on model or actual systems encountered in the universe, atmosphere and biosphere. It is equipped with two dedicated endstations: a VUV Fourier‐transform spectrometer (FTS) for ultra‐high‐resolution absorption spectroscopy (resolving power up to 10⁶) and an electron/ion imaging coincidence spectrometer. The photon characteristics necessary to fulfill its scientific mission are: high flux in the 5–40 eV range, high spectral purity, high resolution, and variable and well calibrated polarizations. The photon source is a 10 m‐long pure electromagnetic variable‐polarization undulator producing light from the very near UV up to 40 eV on the fundamental emission with tailored elliptical polarization allowing fully calibrated quasi‐perfect horizontal, vertical and circular polarizations, as measured with an in situ VUV polarimeter with absolute polarization rates close to unity, to be obtained at the sample location. The optical design includes a beam waist allowing the implementation of a gas filter to suppress the undulator high harmonics. This harmonic‐free radiation can be steered toward the FTS for absorption experiments, or go through a highly efficient pre‐focusing optical system, based on a toroidal mirror and a reflective corrector plate similar to a Schmidt plate. The synchrotron radiation then enters a 6.65 m Eagle off‐plane normal‐incidence monochromator equipped with four gratings with different groove densities, from 200 to 4300 lines mm^?1, allowing the flux‐to‐resolution trade‐off to be smoothly adjusted. The measured ultimate instrumental resolving powers are 124000 (174 µeV) around 21 eV and 250000 (54 µeV) around 13 eV, while the typical measured flux is in the 10¹⁰–10¹¹ photons s^?1 range in a 1/50000 bandwidth, and 10¹²–10¹³ photons s^?1 in a 1/1000 bandwidth, which is very satisfactory although slightly below optical simulations. All of these features make DESIRS a state‐of‐the‐art VUV beamline for spectroscopy and dichroism open to a broad scientific community.     

Molecular structure,spectroscopic (FTIR,FTIR gas phase,FT‐Raman) first‐order hyperpolarizability and HOMO–LUMO analysis of 4‐methoxy‐2‐methyl benzoic acid

Vibrational spectral analysis was carried out for 4‐methoxy‐2‐methyl benzoic acid (4M2MBA) by using Fourier transform infrared (FT‐IR) (solid, gas phase) and FT‐Raman spectroscopy in the range of 400–4000 and 10–3500 cm⁻¹ respectively. The effects of molecular association through O H···O hydrogen bonding have been described by the single dimer structure. The theoretical computational density functional theory (DFT) and Hatree‐Fock (HF) method were performed at 6–311++G(d,p) levels to derive the equilibrium geometry, vibrational wavenumbers, infrared intensities and Raman scattering activities. The scaled theoretical wavenumbers were also shown to be in good agreement with experimental data. The first‐order hyperpolarizability (β₀) of this novel molecular system and related properties (β, α₀ and Δα) of 4M2MBA are calculated using the B3LYP/cc‐pvdz basis set, based on the finite‐field approach. A detailed interpretation of the infrared and Raman spectra of 4M2MBA is reported. The theoretical spectrograms for FT‐IR and FT‐Raman spectra of the title molecule were also constructed and compared with the experimental one. Copyright © 2010 John Wiley & Sons, Ltd.     

Dielectric response of frustrated water down to a single‐molecule contribution

A theory of dielectric response of water under nanoscale confinement was long overdue. This work addresses the problem by establishing a relation between dielectric response and hydrogen‐bond frustration subsumed in a non‐Debye polarization term. The results hold down to the single‐molecule contribution and are validated vis‐à‐vis experimental measurements on a system where dielectric modulation entails removal of a single water molecule. The frustrated dielectric response down to molecular scales is assessed by contrasting two enantiomeric ligands in association with the same protein, with the complexes differing in the removal of a single interfacial water molecule.

     

Density functional theory study on a fluorescent chemosensor device of aza‐crown ether

Three derivatives of alkyl anthracene covalently bonded to aza‐18‐crown‐6 at the nitrogen position, anthracene(CH₂)_n, (n = 1–3) which act as an on–off fluorogenic photoswitch have been theoretically studied using a computational strategy based on density functional theory at B3LYP/6‐31 + G(d,p) method. The fully optimized geometries have been performed with real frequencies which indicate the minima states. The binding energies, enthalpies and Gibbs free energies have been calculated for aza‐18‐crown‐6 ( L ) and their metal complexes. The natural bond orbital analysis is used to explore the interaction of host–guest molecules. The absorption spectra differences between L and their metal ligands, the excitation energies and absorption wavelength for their excited states have been studied by time‐dependent density functional theory with the basis set 6‐31 + G(d,p). These fluorescent sensors and switchers based on photoinduced electron transfer mechanism have been investigated. The PET process from aza‐crown ether to fluorophore can be suppressed or completely blocked by the entry of alkali metal cations into the aza‐crown ether‐based receptor. Such a suppression of the PET process means that fluorescence intensity is enhanced. The binding selectivity studies of the aza‐crown ether part of L indicate that the presence of the alkali metal cations Li⁺, Na⁺ and K⁺ play an important role in determining the internal charge transfer and the fluorescence properties of the complexes. In addition, the solvent effect has been investigated. Copyright © 2014 John Wiley & Sons, Ltd.     

Intramolecular charge transfer in donor‐bridge‐acceptor compounds with paired linearly conjugated or cross‐conjugated pathways

An understanding of intramolecular charge transfer in 2‐D linearly conjugated and cross‐conjugated compounds is necessary for the rational design of molecular electronics, improved solar energy devices, semi‐conducting polymers, and materials with nonlinear optical properties. In this work, the femtosecond transient absorption spectra and kinetics of several donor‐bridge‐acceptor compounds containing cross‐conjugated or linearly conjugated bridging groups were obtained. The veratrole group was used as the donor, and the phthalimide group was used as an acceptor. 2‐D conjugation was achieved by involving two bridging groups arranged cyclically between the donor and acceptor. The donor and acceptor were bridged by m‐phenylene in the cross‐conjugated compounds or 2,5‐thiophene in the linearly conjugated compounds. We found slower charge separation times and slower charge recombination times in the compounds containing cyclic cross‐conjugated bridging groups than in those containing the cyclic linearly conjugated groups in polar solvent. Charge separation rates that were found to be dependent on solvent were observed in the donor‐bridge‐acceptor compounds. Copyright © 2014 John Wiley & Sons, Ltd.     

Revisiting the combined photon echo and single‐molecule studies of low‐temperature dynamics in a dye‐doped polymer

The photon echo (PE) spectroscopy and single‐molecule spectroscopy (SMS) may be combined to give a very powerful tool for comprehensive study of low‐temperature dynamics in dye‐doped disordered solids (polymers, glasses). At the same time, this type of studies are likely to reveal discrepancies when comparing characteristic times of optical dephasing T₂ and single‐molecule zero‐phonon spectral lines (ZPL) broadening obtained from PE and SMS, correspondingly, for tetra‐tert‐butylterrylene in polyisobutylene in the temperature range of a few–dozen of Kelvins [see Phys. Status Solidi B 241 , 3480 and 3487 (2004)]. Inexplicably, PE‐experiments demonstrated T₂‐times to be much shorter than it is sufficient to cause the corresponding ZPL broadening. Here we experimentally solve this problem and show that at T = 4.5–15 K the incoherent PE gives T₂‐times which correspond to the narrowest SM ZPL. On the SM‐level there is a pronounced additional ZPL‐broadening due to spectral diffusion processes which are strongly dependent on the characteristics time of the measurement (tens of nanoseconds for PE and seconds for SMS). There is also a broad distribution of ZPL spectral widths for different SMs due to different local environments, that contribute differently to both the optical dephasing and the spectral diffusion processes, but always in addition to the value of inverse optical dephasing times measured using a PE technique.

     

Evolution of excess electron binding motifs under both internal‐push (from exo C–F bonds) and external‐push (from endo C–F bonds) electron effects in endohedral metallofullerenes with endo C–F bonds

How does the endo C–F bond influence the excess electron binding motif? For lithium‐doped endohedral perfluorofullerenes with endo C–F bonds, under both internal‐push (from exo C–F bonds) and external‐push (from endo C–F bonds) electron effects, the singly occupied molecular orbital electron cloud of the sphere‐like Li···F₈@C₆₀F₅₂ (D₂) is partially dispersed within the σ_p–s antibonding orbital of endo C–F bonds and the space between C^δ+–F_endo^δ– double electric layers, which makes Li···F₈@C₆₀F₅₂ have partial excess electron (electride characteristics) and partial lithium salt characteristics, while in the tube‐like Li···F₂@C₆₀F₅₈ (C_s), as the Li is changing from approaching F to keeping away from F and to approaching another one, the singly occupied molecular orbital electron cloud is mainly dispersed from within the p orbital of the short endo C–F bond to within the middle of the two F atoms and again to within the p orbital of the short endo C–F bond, which indicates an evolution from lithium salt characteristic to excess electron characteristic, and again to lithium salt characteristic. Copyright © 2012 John Wiley & Sons, Ltd.     

In–Ga–Zn–O MESFET with transparent amorphous Ru–Si–O Schottky barrier

Rectifying transparent amorphous Ru–Si–O Schottky contacts to In–Ga–Zn–O have been fabricated by means of reactive sputtering without any annealing processes nor semiconductor surface treatments. The ideality factor, effective Schottky barrier height and rectification ratio are equal to 1.6, 0.9 eV and 10⁵ A/A, respectively. Ru–Si–O/In–Ga–Zn–O Schottky barriers were employed as gate electrodes for In–Ga–Zn–O metal–semiconductor field‐effect transistors (MESFETs). MESFET devices exhibiting on‐to‐off current ratio at the level of 10³ A/A in a voltage range of 2 V, with subthreshold swing equal to 420 mV/dec were demonstrated. A channel mobility of 7.36 cm²/V s was achieved. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nanoscale C‐Rich SixC1−x Bus/Ring Waveguide Based Cross‐Wavelength Data Converter

The carbon‐rich silicon carbide (C‐rich Si_xC_1?x) micro‐ring channel waveguide with asymmetric core aspect is demonstrated for all‐optical cross‐wavelength pulsed return‐to‐zero on‐off keying (PRZ‐OOK) data conversion. Enhanced nonlinear optical Kerr switching enables 12‐Gbit per second data processing with optimized modulation depth. The inverse tapered waveguide at end‐face further enlarges the edge‐coupling efficiency, and the asymmetric channel waveguide distinguishes the polarization modes. To prevent data shape distortion, the bus/ring gap spacing is adjusted to control the quality factor (Q‐factor) of the micro‐ring. Designing the waveguide cross section at 500 × 350 nm² provides the C‐rich Si_xC_1?x channel waveguide to induce strong transverse electric mode (TE‐mode) confinement with a large Kerr nonlinearity of 2.44 × 10^?12 cm² W^?1. Owing to the trade‐off between the Q‐factor and the on/off extinction ratio, the optimized bus/ring gap spacing of 1400 nm is selected to provide a coupling ratio at 5–6% for compromising the modulation depth and the switching throughput. Such a C‐rich Si_xC_1?x micro‐ring with asymmetric channel waveguide greatly enhances the cross‐wavelength data conversion efficiency to favor its on‐chip all‐optical data processing applications for future optoelectronic interconnect circuits.     

Palladium‐catalyzed cyclization of 2‐alkynyl‐N‐ethanoyl anilines to indoles: synthesis,structural, spectroscopic,and mechanistic study

This study reports a facial regio‐selective synthesis of 2‐alkyl‐N‐ethanoyl indoles from substituted‐N‐ethanoyl anilines employing palladium (II) chloride, which acts as a cyclization catalyst. The mechanistic trait of palladium‐based cyclization is also explored by employing density functional theory. In a two‐step mechanism, the palladium, which attaches to the ethylene carbons, promotes the proton transfer and cyclization. The gas‐phase barrier height of the first transition state is 37 kcal/mol, indicating the rate‐determining step of this reaction. Incorporating acetonitrile through the solvation model on density solvation model reduces the barrier height to 31 kcal/mol. In the presence of solvent, the electron‐releasing (–CH₃) group has a greater influence on the reduction of the barrier height compared with the electron‐withdrawing group (–Cl). These results further confirm that solvent plays an important role on palladium‐catalyzed proton transfer and cyclization. For unveiling structural, spectroscopic, and photophysical properties, experimental and computational studies are also performed. Thermodynamic analysis discloses that these reactions are exothermic. The highest occupied molecular orbital?lowest unoccupied molecular orbital gap (4.9–5.0 eV) confirms that these compounds are more chemically reactive than indole. The calculated UV–Vis spectra by time‐dependent density functional theory exhibit strong peaks at 290, 246, and 232 nm, in good agreement with the experimental results. Moreover, experimental and computed ¹H and ¹³C NMR chemical shifts of the indole derivatives are well correlated. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of III‐nitride polarization on VOC in p–i–n and MQW solar cells

We performed detailed studies of the effect of polarization on III‐nitride solar cells. Spontaneous and piezoelectric polarizations were assessed to determine their impacts upon the open circuit voltages (V_OC) in p–i(InGaN)–n and multi‐quantum well (MQW) solar cells. We found that the spontaneous polarization in Ga‐polar p–i–n solar cells strongly modifies energy band structures and corresponding electric fields in a way that degrades V_OC compared to non‐polar p–i–n structures. In contrast, we found that piezoelectric polarization in Ga‐polar MQW structures does not have a large influence on V_OC compared to non‐polar MQW structures. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A combined experimental and density functional study of 1‐(arylsulfonyl)‐2‐R‐4‐chloro‐2‐butenes reactivity towards the allylic chlorine

Nucleophilic substitution and dehydrochlorination reactions of a number of the ring‐substituted 1‐(arylsulfonyl)‐2‐R‐4‐chloro‐2‐butenes are studied both experimentally and theoretically. The developed synthetic procedures are characterized by a general rapidity, cheapness, and simplicity providing moderate to high yields of 1‐arylsulfonyl 1,3‐butadienes (48–95%), 1‐(arylsulfonyl)‐2‐R‐4‐(N,N‐dialkylamino)‐2‐butenes (31–53%), 1‐(arylsulfonyl)‐2‐R‐2‐buten‐4‐ols (37–61%), and bis[4‐(arylsulfonyl)‐3‐R‐but‐2‐enyl]sulfides (40–70%). The density functional theory B3LYP/6‐311++G(2d,2p) calculations of the intermediate allylic cations in acetone revealed their high stability occurring from a resonance stabilization and hyperconjugation by the SO₂Ar group. The reactivity parameters estimated at the bond critical points of the diene/allylic moiety display a high correlation (R² > 0.97) with the Hammett (σ_p) constants. 1‐Arylsulfonyl 1,3‐butadienes are characterized by a partly broken π conjugated system, which follows from analysis of the two‐centered delocalization (δ) and localization (λ) index values. The highest occupied molecular orbital energies of 1‐arylsulfonyl 1,3‐butadienes are lower than those of 1,3‐butadiene explaining their low reactivity towards the Diels–Alder condensation. Copyright © 2015 John Wiley & Sons, Ltd.     

Ultra‐thin optical grade scCVD diamond as X‐ray beam position monitor

Results of measurements made at the SIRIUS beamline of the SOLEIL synchrotron for a new X‐ray beam position monitor based on a super‐thin single crystal of diamond grown by chemical vapor deposition (CVD) are presented. This detector is a quadrant electrode design processed on a 3 µm‐thick membrane obtained by argon–oxygen plasma etching the central area of a CVD‐grown diamond plate of 60 µm thickness. The membrane transmits more than 50% of the incident 1.3 keV energy X‐ray beam. The diamond plate was of moderate purity (～1 p.p.m. nitrogen), but the X‐ray beam induced current (XBIC) measurements nevertheless showed a photo‐charge collection efficiency approaching 100% for an electric field of 2 V µm^?1, corresponding to an applied bias voltage of only 6 V. XBIC mapping of the membrane showed an inhomogeneity of more than 10% across the membrane, corresponding to the measured variation in the thickness of the diamond plate before the plasma etching process. The measured XBIC signal‐to‐dark‐current ratio of the device was greater than 10⁵, and the X‐ray beam position resolution of the device was better than a micrometer for a 1 kHz sampling rate.     

DFT,FT‐Raman,FT‐IR and NMR studies of 2‐fluorophenylboronic acid

The experimental and theoretical vibrational spectra of 2‐fluorophenylboronic acid (2fpba) were studied. The Fourier transform Raman and Fourier transform infrared spectra of the 2fpba molecule were recorded in the solid phase. The structural and spectroscopic analysis of the molecule was carried out by using Hartree‐Fock and density functional harmonic calculations. For the title molecule, only one form was found to be the most stable structure, by using B3LYP level with the 6‐31++G(d,p) basis set. Selected experimental bands were assigned and characterized on the basis of the scaled theoretical wavenumbers by their total energy distribution (TED). The ¹H and ¹³C nuclear magnetic resonance (NMR) chemical shifts of the 2fpba molecule were calculated using the Gauge‐Invariant‐ atomic orbital (GIAO) method in DMSO solution using IEF‐PCM model and compared with the experimental data. Finally, geometric parameters, vibrational wavenumbers and chemical shifts were compared with available experimental data of the molecule. Copyright © 2009 John Wiley & Sons, Ltd.     

Electronic and structural effects on the nonlinear optical behavior in π‐conjugated structure bis(4‐nitrophenyl) carbonate: a vibrational spectroscopic approach

Fourier transform (FT)‐Raman and infrared (IR) spectra of the nonlinear optical (NLO) material bis(4‐nitrophenyl) carbonate were recorded and analyzed. The geometry, first hyperpolarizability and harmonic vibrational wavenumbers were calculated with the help of Becke3–Lee–Yang–Parr density functional theory method. The detailed interpretation of the vibrational spectra was carried out with the aid of normal coordinate analysis following the scaled quantum mechanical force field methodology. The second‐order NLO properties of the molecule were studied by the Kurtz and Perry powder reflection technique. Stability of the molecule arising from hyperconjugative interactions leading to its NLO activity and charge delocalization were analyzed using natural bond orbital analysis. Copyright © 2010 John Wiley & Sons, Ltd.     

Molecular structure,vibrational spectroscopic,first‐order hyperpolarizability and HOMO,LUMO studies of 3‐hydroxy‐2‐naphthoic acid hydrazide

The Fourier‐transform infrared spectrum of 3‐hydroxy‐2‐naphthoic acid hydrazide (3H2NAH) was recorded in the region 4000–400 cm⁻¹. The Fourier‐transform Raman spectrum of 3H2NAH was also recorded in the region 3500–10 cm⁻¹. Quantum chemical calculations of energies, geometrical structure and vibrational wavenumbers of 3H2NAH were carried out by density functional theory (DFT/B3LYP) method with 6‐31G(d,p) as basis set. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. The values of the electric dipole moment (µ) and the first‐order hyperpolarizability (β) of the investigated molecule were computed using ab initio quantum mechanical calculations. The UV spectrum was measured in ethanol solution. The calculation results also show that the 3H2NAH molecule might have microscopic nonlinear optical (NLO) behavior with non‐zero values. A detailed interpretation of the infrared and Raman spectra of 3H2NAH is also reported based on total energy distribution (TED). The calculated HOMO and LUMO energies shows that charge transfer occur within the molecule. The theoretical FT‐IR and FT‐Raman spectra for the title molecule have also been constructed. Copyright © 2009 John Wiley & Sons, Ltd.