Isolation and characterization of conformational isomers of N,N′‐bis(3,5‐dichlorosalicylidene)‐2,2′‐ethylenedianiline: crystal structure,photoluminescence, and density functional theory calculation

We have isolated two isomeric solids 1 and 2 of N,N′‐bis(3,5‐dichlorosalicylidene)‐2,2′‐ethylenedianiline and characterized by IR, UV/Vis, X‐ray powder diffraction, thermogravimetric analysis/differential thermal analysis, and X‐ray crystallography. Although the solids are same formulas, each shows different colors and crystal structures. Orange solid ( 1 ) shows endo conformation while yellow solid ( 2 ) exhibits exo form depending on packing modes. UV/Vis spectra of 1 and 2 appear very similar patterns in the solid state; however, the bands of 1 are slightly red‐shifted compared with those of 2 . 1 displays a strong fluorescent emission band at ~582 nm while 2 shows an intense fluorescent signal at ~563 nm. The charge density populations of 1 and 2 have been studied by computational simulations using density functional theory at pbe1pbe/6‐311G** level. The calculated highest occupied molecular orbital and lowest unoccupied molecular orbital energies of 1 and 2 confirm that charge transfer occurs within the organic molecules. The energy difference of HOMO‐LUMO in 1 is smaller slightly than that of 2 about 0.05 eV (~17 nm). Copyright © 2014 John Wiley & Sons, Ltd.     

Compounds with π(loc) → π*(deloc) electronic transitions and their solvatochromism

Molecular structures possessing atomic sites that contribute a non‐bonding electron pair to their π system (e.g. nitrogen atoms with sp² hybridization in pyrroles and anilines) usually exhibit a first absorption band whose solvatochromism is, surprisingly, sensitive only to the polarizability of the medium even though they are dipolar. As shown here, this solvatochromic behavior is a result of the first electronic transition in these compounds occurring from a substantially localized π orbital to a substantially delocalized π* orbital in the molecular structure. The high electronic delocalization present leads to a marked bathochromic band shift as the polarizability of the medium increases. It is especially relevant that this solvatochromism, which is because of the polarizability of the medium, explains the spectral shift that is only because of the redistribution of the electrons of the solvent molecules. It is important to take into account that this electronic redistribution happens instantaneously in this process. Copyright © 2015 John Wiley & Sons, Ltd.     

Deep UV resonance Raman spectroscopic study of CnF2n+2 molecules: the excitation of C–C σ bond

The σ–σ* transition of C–C bond in C_nF_2n+2 molecules was studied by deep UV resonance Raman spectroscopy. With the C–C σ bond selectively excited by the deep UV laser at 177.3 nm, the resonance Raman spectra of C_nF_2n+2 molecules were obtained on our home‐assembled deep UV Raman spectrograph. The Raman bands at 1299, 1380 and 2586 cm⁻¹ due to the C–C skeletal stretching modes are evidently enhanced owing to the resonance Raman effect. Based on the resonance Raman spectra and theoretical calculation results, it is proposed that the electronic geometry of C_nF_2n+2 molecules at the σσ* excited state is displaced along the directions perpendicular and parallel to the C–C skeleton, and the excited C–C bond is not dissociative due to the delocalization of the excited electron in σ* orbital. Copyright © 2012 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.     

Kinetics and thermochemistry of the unusual [2π + 2σ + 2σ]‐cycloaddition of quadricyclane with some dienophiles

Kinetic parameters of the unusual [2π + 2σ + 2σ]‐cycloaddition reactions of quadricyclane ( 1 ) with tetracyanoethylene ( 2 ), 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione ( 3 ), N‐phenylmaleimide ( 4 ), and diethyl azodicarboxylate ( 5 ) are determined experimentally. Additionally, the enthalpies of 1  +  2 reaction in 1,4‐dioxane solution (?236.6 ± 1.0 kJ mol^?1) and 1  +  3 reaction in toluene (?255.0 ± 2.8 kJ mol^?1) are determined calorimetrically and shown to be the largest in absolute magnitude among all known cycloaddition reactions involving these dienophiles. Solvent effect on the rate of 1 + 3 reaction in 11 solvents is studied and found to be moderate and similar to that of the conventional Diels‐Alder and ene reactions. The difference in the reaction rate constants of 1 with different dienophiles can be up to 9 orders of magnitude and is mainly caused by the difference in activation enthalpies. This difference is not correlated with the standard enthalpies of reactions and is likely the result of high sensitivity of the [2π + 2σ + 2σ] reaction rates to the energy of donor‐acceptor interactions between the reactants.     

Electronic transport time through mesoscopic devices with contact barriers

Information about the transport time of electrons through a quasi one-dimensional sample is obtained by calculating the energy auto-correlation function of the conductance. Depending on the length of the sample and its coupling to the external device (here modelled by perfectly conducting leads), the transport time undergoes a smooth crossover between two different limiting regimes. In the case of long samples and good coupling it coincides with the diffusion time. In the opposite limit of short and weakly coupled systems, however, the transport time is given by the reciprocal of the quantum mechanical decay width into the leads. The transition between both regimes is discussed in terms of a few model independent concepts.     

Theoretical insights into the host–guest interactions between [6]cycloparaphenyleneacetylene and its anthracene‐containing derivative and fullerene C70

The host–guest complexes formed with [6]cycloparaphenyleneacetylene ([6]CPPA) and its anthracene‐containing derivative ([6]CPPAs) hosts and fullerene C₇₀ guest were explored by density functional calculations. Besides two previously reported configurations in which C₇₀ guest is standing or lying in the cavity of the host, we found a new kind of configuration in which C₇₀ guest is half‐lying in the cavity of the host. More interestingly, the calculated results revealed that the fine‐tuning deformations occur readily during the formations of the complexes, suggesting that both [6]CPPA and [6]CPPAs are highly elastic host molecules. The large host–guest binding energies indicate that both two host molecules, [6]CPPA and [6]CPPAs, have excellent encapsulation ability for C₇₀ guest, and the [6]CPPAs even has much better encapsulation ability for C₇₀ than [6]CPPA. Furthermore, the host–guest interactions regions were detected and visualized in real space based on the electron density and reduced density gradient. Additionally, ¹H NMR spectra of those three different kinds of configurations mentioned earlier have been calculated with gage‐independent atomic orbital method, which may be helpful for further experimental characterizations in future. Copyright © 2014 John Wiley & Sons, Ltd.     

Growth,shrinkage, and stability of interfacial oxide layers between directly bonded silicon wafers

Models for the growth and shrinkage of an interfacial oxide layer and for the stability of the interfacial oxide layer are formulated. Predictions of these models are compared to results obtained by high-resolution transmission electron microscopy. Wafers containing different concentrations of oxygen interstitials are bonded. Depending on the starting concentration of oxygen interstitials in the wafers, the interfacial oxide layer grows or shrinks during long-time annealing at high temperatures. For much shorter annealing times, local disintegration of the oxide layer may occur, which is less severely influenced by the concentration of oxygen interstitials. Rather, it depends on the thickness of the interfacial oxide layer. The influence of rotational misorientation is examined by rotating wafers around their common axes perpendicular to a wafer plane and subsequent bonding. Above a critical angle of about 1–3°, a continuous oxide layer is formed, whereas below this critical angle, sufficiently thin oxide layers disintegrate.Also at Microelectronics Center of North Carolina, USA     

Theoretical studies on aromaticity of selected hydroxypyrones and their cations and anions. Part 2. Electron delocalisation in the OCCO group

Electron delocalisation in the OCCO part of hydroxypyrones with two exocyclic oxygens linked by two carbon atoms was studied using well‐known aromaticity indices like: HOMA, EN, GEO, NICS(0) and NICS(1). This part of hydroxypyrones is very important due to the fact that the two exocyclic oxygens of deprotonated hydroxypyrone units are responsible for metal ion binding. Values of the aromaticity indices were obtained for geometries calculated by several theoretical methods (HF, SVWN, B3LYP and B1LYP) with 6‐311 ++ G(d,p) basis set. Electron delocalisation in the corresponding cations and anions was also considered. The data obtained in this work revealed that the relative delocalisation order in the OCCO group is the same as the aromaticity order determined earlier for the heterocyclic rings of hydroxypyrones (anions < neutral molecule < cation). The problem of quasiaromaticity in neutral hydroxypyrones and their cations is also considered and discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Assessment of the aromaticity of borepin rings by spectroscopic,crystallographic and computational methods: a historical overview

This review presents a chronological discussion of the evolution of our conceptual and experimental understanding of aromaticity as pertaining to the borepin ring structure. Borepin is the boron‐containing charge‐neutral analogue of the carbocyclic tropylium ion, and many molecular variations involving the borepin motif have been synthesized over the past half century. The aromaticity of the borepin system has been probed with ultraviolet–visible (UV–vis), photoluminescence and infrared (IR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, X‐ray crystallography and computational analysis. Recently, the focus of borepin‐containing compounds has shifted to π‐electron materials, building on the foundation of a firm understanding of the physical organic properties of the borepin motif that will allow for electronic fine‐tuning toward desired applications. Copyright © 2015 John Wiley & Sons, Ltd.     

Study of annihilation in two mesons in the momentum range between 50 to 400 MeV/c with OBELIX

We measured the in flight annihilation frequencies and cross sections of reactions and K⁺K_S in the antineutron momentum range between 50 and 400 MeV/c. The annihilation frequencies of these channels from the different allowed initial states were calculated and some information about the annihilation dynamics were obtained. The first determination of the D-wave contribution in this momentum range was also obtained.     

Synthesis,spatial structure and spectral properties of pyrylo‐4 (thio) squaraines variously substituted in cyclobutene moiety

Synthetic routes have been developed to a number of (thio) squaraine dyes containing the residues of CH‐acids at the central cyclobutene ring. The electronic and spatial structure as well as the chemical conversions and optical behaviour of the compounds obtained have been studied both theoretically and by X‐ray diffraction analysis, ¹H NMR and electronic spectroscopy. As shown, the electronic nature and sterical characteristics of the central ring substituents give rise to some general conformational features and crystal packing regularities and also govern the spectral position of the first π–π^* absorption band. The structure–property relationships established in the study provide guidance for the purposeful design of deeply coloured (thio) squaraines. Copyright © 2015 John Wiley & Sons, Ltd.     

Orthorhombic YAlO3 – a novel many‐phonon SRS‐active crystal

In single crystals of orthorhombic YAlO₃, widely known as a host‐matrix for Ln³⁺‐lasant ions, many‐phonon stimulated Raman scattering interactions as well as different manifestations of cascaded and cross‐cascaded nonlinear χ⁽³⁾↔χ⁽³⁾ processes are initiated by picosecond laser pulses. The scientific and applicative potential of YAlO₃ crystals is considerably expanded by the demonstration of its SRS properties. In particular, the studies revealed the manifestation of eight χ⁽³⁾‐active vibrational modes. The corresponding Stokes and anti‐Stokes lines have been assigned and the steady‐state Raman gain coefficients related to the strongest phonon mode have been estimated. In addition, a short review presents the stimulated emission channels of its Ln³⁺‐ions together with some χ⁽³⁾‐nonlinear laser properties of crystals belonging to the binary Y₂O₃‐Al₂O₃ system.     

Solvatochromic properties of long alkyl chain π* indicators: comparison of N,N‐dialkyl‐4‐nitroanilines and alkyl 4‐nitrophenyl ethers

Hydrophobic forms of the N,N‐dialkyl‐4‐nitroaniline (DNAP) (p‐O₂NC₆H₄NR₂) ( 1a–f ) and alkyl‐4‐nitrophenyl ether (p‐O₂NC₆H₄OR) ( 2a–c ) solvatochromic π* indicators have been characterized and compared with respect to: (a) solvatochromic bandshape, (b) sensitivity expressed as ?s , ( / d π * ), and (c) trends in ? s with increasing length of alkyl chain(s) on the probe molecule. ? Octyl 4‐nitrophenyl ether (p‐O₂NC₆H₄OC₈H₁₇) ( 2b ) and ? decyl 4‐nitrophenyl ether (p‐O₂N C₆H₄ OC₁₀H₂₁) ( 2c ) were synthesized and their solvatochromic UV/Vis absorption bands were found to maintain a Gausso‐Lorentzian bandshape for the indicators in non‐polar and alkyl substituted aromatic solvents, for example, hexane(s) and mesitylene. Corresponding absorption bands for 1a–f display increasing deviation from a Gausso‐Lorentzian shape in the same solvents as the alkyl chains on the indicator are increased in length all the way to C₁₀ and C₁₂, for example, N,N‐didecyl‐4‐nitroaniline (p‐O₂NC₆H₄N (C₁₀H₂₁)₂) and N,N‐didodecyl‐4‐nitroaniline (p‐O₂NC₆H₄N (C₁₂H₂₅)₂) ( 1d–f ). A plot of ? s versus C_n follows a 1st order decay for the DNAP indicators but is linear for the alkyl 4‐nitrophenyl ethers. A discussion of how the long alkyl chains on the two types of indicators affect the orientation and overlap of n and π * orbitals, and resulting solvatochromic bands is presented. For DNAP, overextending the alkyl chains to obtain greater hydrophobic character may cause the alkane component to dominate solute‐solvation processes at the expense of the probe's fundamental solvatochromic character. Copyright © 2007 John Wiley & Sons, Ltd.     

Diffusion of silicon in titanium nitride films. Efficiency of TiN barrier layers

Two kinds of reactively evaporated titanium nitride films with columnar (B ₀ films) and fine-grained film structure (B ₊ films) have been examined as diffusion barriers, preventing the silicon diffusion in silicon devices. The silicon diffusion profiles have been investigated by 2 MeV ⁴He⁺ Rutherford backscattering spectrometry (RBS) after annealing at temperatures up to 900° C, in view of application of high-temperature processes. The diffusivity from 400 to 900° C: D (m² s^–1)=2.5×10^–18 exp[–31 kJ/mol/(RT)] in B ₀ layers and D (m² s^–1)=3×10^–19 exp[–26 kJ/mol/(RT) in B ₊ TiN layers. The diffusivities determined correspond to grain boundary diffusion, the difference being due to the different microstructure. The very low diffusivity of silicon in B ₊ TiN layer makes it an excellent high-temperature barrier preventing silicon diffusion.     

Thermal reaction of electron deficient 4‐oxo‐4H‐pyrazole 1,2‐dioxide with cycloheptatriene: the first examples of the formation of an endo‐[4π + 6π]‐cycloadduct and an intramolecular 1,3‐dipolar reaction leading to a heterocage

The reaction of 3,5‐bis(methoxycarbonyl)‐4‐oxo‐4H‐pyrazole 1,2‐dioxide (1a) with 1,3,5‐cycloheptatriene (2b) gave a mixture of the novel endo‐[4 + 6]‐cycloadduct (4ab), anti‐exo‐[4 + 2]‐cycloadduct (5ab), and the heterocage (6ab) derived from the intramolecular 1,3‐dipolar cycloaddition reaction of the syn‐endo‐[4 + 2]‐cycloadduct. Analogous endo‐[4 + 6] selectivity in 1,3‐dipolar cycloadditions has not been reported previously. The X‐ray analysis indicates that 6ab has a very long N_sp3–N_sp3 bond distance of 1.617(4) Å. The cycloaddition behaviour is discussed on the basis of transition‐state structures optimized at the B3LYP/6‐31G(d) level of theory, from which predictions of the peri‐, regio‐, and stereoselectivities agreed well with the experimental results. Copyright © 2012 John Wiley & Sons, Ltd.     

On shadow elimination after moving region segmentation based on different threshold selection strategies

A popular approach for detecting moving object regions in video sequences is the application of the background subtraction technique. According to this technique the background (reference) image is subtracted from the current image frame and the moving parts are detected by the selection of a suitable threshold. In this paper we present our work to discriminate the moving pixels of the generated difference images from the relatively stationary pixels through the use of three different threshold selection strategies, namely, (i) ‘3σ edit rule’, (ii) rule utilizing the Hampel identifier, and (iii) rule based on an ad hoc selection of threshold. Further, after segmentation a method of classification, based on a moving shadow search technique, previously developed by the authors, has been applied to segregate the moving shadow region from the actual moving object. The speed-up achieved through the use of the three aforementioned techniques on the core moving shadow search process, compared to that where no such process has been applied, has been documented. The final outcomes of applying the shadow detection technique after segmenting using each of the threshold selection strategies, one at a time, on some indoor video sequences have been demonstrated and comparison of the methods made.