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.     

A computational study of model hydrogen-, halogen-, beryllium- and magnesium-bonded complexes of aziridine derivatives

ABSTRACT

A computational study of the complexes F^?/H₂O…Z-aziridine, Z-aziridine…BeH₂/MgH₂ and F^?/H₂O…Z-aziridine…BeH₂ /MgH₂ (Z = Cl, H, Li) was undertaken in order to investigate the non-covalent interactions operative in the dimers and to assess their interplay in the trimer complexes. The halogen- and hydrogen-bonds between the O and Z atoms in F^?/H₂O…Z-aziridine are enhanced in the trimers by the Be(Mg) bond and vice versa, but the lithium bond is hardly affected. In the trimers containing F^?, the H bond is more dominant than the Be(Mg) bond, whereas the Be(Mg) bond is more dominant in the halogen- and lithium-bonded analogues. On the other hand, the Be(Mg) bond makes the major contribution to the energetic stability of all of the trimers containing H₂O.     

Azure A chloride: computational and spectroscopic study

Fourier transform Raman and IR as well as UV–visible spectra of the phenothiazine dye Azure A chloride, 3‐amino‐7‐(dimethylamino) phenothiazin‐5‐ium chloride were recorded and analyzed. The spectral interpretation was done following full structure optimization and vibrational wavenumber calculations based on the density functional theory (DFT) using the standard B3LYP/6‐31G(d) basis set. The N H stretching wavenumber is found to be lowered owing to intermolecular N H···S hydrogen bonding. The downshift of C H stretching wavenumber is discussed. The first hyperpolarizability of the dye is calculated. Time‐dependent density functional theory (TD‐DFT) calculations of electronic spectra were performed on the optimized structure and compared with the experimental UV–visible spectrum. The atomic net charges of the molecule reveal the  M effect of the nitrogen atoms in the molecule. Stability of the molecule arising from hyperconjugative interactions leading to its nonlinearity and bioactivity, charge delocalization and mesomeric effects have been analyzed using natural bond orbital (NBO) analysis. Copyright © 2008 John Wiley & Sons, Ltd.     

A radar-infrared compatible broadband absorbing surface:Design and analysis

A radar-infrared compatible stealth surface is designed and analyzed. Without modifying the radar absorbing material(RAM), the design can theoretically achieve radar-infrared compatibility and broadband radar absorption through surface patterns and structures. A transmission-line-based model(TLM) is developed to analyze the radar absorbing performance of the surface. Optimization of the structure geometries is conducted aiming to maximize the-10 d B absorption bandwidth in 2–18 GHz. Surface with optimized structure geometries exhibits a superior absorption bandwidth, more than twice the bandwidth of the original 1.5 mm RAM slab, while maintaining a relatively low infrared emissivity.     

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.     

Numerical study on three-dimensional C-J detonation waves: detailed propagating mechanism and existence of OH radical

An unsteady three-dimensional simulation is performed for a hydrogen/air C–J detonation in a rectangular tube, where a detailed chemical reaction model is used to reveal the C–J detonation structure. In this simulation, detailed propagating detonation structures for a diagonal mode are described in three-dimensions. The detonation front structures, the line of triple points, and the strong explosions at the corners of the rectangular tube are revealed by using a three-dimensional numerical visualization. From the spatial isosurface profiles of H₂ mass fraction, it is confirmed that the triple point lines have a role of “shutter” to generate unburned gas pockets and become of a ring shape behind the detonation front due to its explosion. The explosion process and its influence on an induction delay are observed by visualizing the spatial isosurface profiles of OH mass fraction. Moreover, a high “peninsula-shaped” OH mass fraction area, which has been experimentally reported, is reproduced on the side wall of the rectangular tube.     

Selectivity in metal ions mediated C–N bond formation reactions of 8‐aminoquinoline derivatives

Cyclisation reactions via C–N bond formation of 2‐bromo‐N‐(quinolin‐8‐yl)propanamide (I) and 2‐bromo‐N‐(quinolin‐8‐yl)acetamide (II) are facilitated by metal salts such as copper (+2), nickel (+2) perchlorate or nitrate and palladium (+2) acetate. Nickel (+2) perchlorate mediated reaction of I and II resulted in C–N bond formation to give corresponding perchlorate salts of three fused six‐membered heterocyclic rings. The copper (+2) mediated reactions are found to be solvent dependent for I, but independent for II. Copper mediated reaction of II gave cyclised product analogous to the one obtained from reaction of II with nickel (+2) perchlorate in methanol or ethanol. But the reaction of I with copper (+2) perchlorate in methanol gave C–N bonded methoxylated cyclised product. This reaction took place in two steps, cyclisation followed by methoxylation. The source of methoxy group is confirmed to be from methanol by deuterium labelling experiments. Whereas similar copper mediated reaction of I in ethanol led to nucleophilic substitution of bromide ion by ethoxide. The structures of the salts of fused heterocyclic compounds were determined and their fluorescence emissions were studied. The large difference in fluorescence emission of compound V formed from copper mediated reaction in ethanol from the compound VI formed from nickel mediated reaction in methanol or ethanol, this feature can be used to distinguish nickel (+2) and copper (+2) ions. The reaction of II with palladium (+2) acetate resulted in the formation of C–N bond to yield the corresponding heterocycle as bromide salt; without anion exchange. Copyright © 2011 John Wiley & Sons, Ltd.     

Sulfonyl nitrenes from different sources: computational study of formation and transformations

The formation of sulfonyl nitrenes RSO₂N (R = Me, p‐Tol, CF₃) from different sources, such as sulfonyl azides RSO₂N₃, N‐halosulfonamides RSO₂NHHal, salts RSO₂NNaCl, N‐hydroxysulfonamides RSO₂NHOH and sulfonylimino‐λ³‐iodanes ArI = NSO₂R or ‐bromanes, by elimination of neutral molecules (N₂, HCl, NaCl, H₂O and ArHal, respectively) was studied theoretically at the density functional theory and second‐order Møller‐Plesset perturbation theory using the 6‐311++G(d,p) and cc‐pVTZ basis sets. The originally formed singlet nitrenes suffer nonradiative intersystem crossing to the triplet state (S₁ ? T₁) or, sometimes, undergo spontaneous barrierless pseudo‐Curtius rearrangement into the corresponding sulfonylamines RN = SO₂. The activation barriers decrease in the order (kcal/mol): RSO₂NHHal ~ RSO₂NHOH (60–70) ≥ RSO₂N(Na)Hal (40–50) > RSO₂N₃ (35) > RSO₂N = IPh (9–13) ≥ RSO₂N = BrC₆H₄CF₃ (4–8). Copyright © 2013 John Wiley & Sons, Ltd.     

A computational study of the thermolysis of β‐hydroxy ketones in gas phase and in m‐xylene solution

Theoretical calculations at the M05‐2X/6‐31+G(d) level of theory have been carried out in order to explore the nature of the mechanism of the thermal decomposition reactions of the β‐hydroxy ketones, 4‐hydroxy‐2‐butanone, 4‐hydroxy‐2‐pentanone, and 4‐hydroxy‐2‐methyl‐2‐pentanone in gas phase and in m‐xylene solution. The mechanism proposed is a one‐step process proceeding through a six‐membered cyclic transition state. A reasonable agreement between experimental and calculated activation parameters and rate constants has been obtained, the tertiary : secondary : primary alcohol rate constant ratio being calculated, at T = 503.15 K, as 5.9:4.7:1.0 in m‐xylene solution and 44.1:5.0:1.0 in the gas phase, compared with the experimental values, 3.7:1.3:1.0 and 13.5:3.2:1.0, respectively. The progress of the thermal decomposition reactions of β‐hydroxy ketones has been followed by means of the Wiberg bond indices. The lengthening of the O₁–C₂ bond with the initial migration of the H₆ atom from O₅ to O₁ can be seen as the driving force for the studied reactions. Calculated synchronicity values indicate that the mechanisms correspond to concerted and highly synchronous processes. The transition states are “advanced”, nearer to the products than to the reactants. Copyright © 2012 John Wiley & Sons, Ltd.     

Changes of electron density in the OHN hydrogen bond upon proton transfer in complexes of phenols with trimethylamine: DFT study

The intermolecular hydrogen bonds in phenol–trimethylamine complexes were investigated by Bader Atom in Molecules (AIM) theory. The AIM parameters of the bond critical points (BCPs) of the O···H, N···H, and CO bonds as well as those of the phenol ring critical point (RCP) were analyzed as functions of the proton‐transfer degree. Transfer of the proton from donor to acceptor changes not only the electron density of the hydrogen bridge, but also the electron cloud in the proton donor. The differences between the proton donors in relation to their pK_a values are seen in the systematic changes of the AIM parameters. Copyright © 2008 John Wiley & Sons, Ltd.     

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 UV,blue and green up-conversion luminescence of PbF2+GeO2:Er2O3 pumped with 650 nm

A detailed study of the spectroscopic properties of the PbF₂+GeO₂:Er₂O₃ vitroceramic sample upon 650 nm excitation was investigated. The absorption, emission, excitation spectra, and time-resolved spectra have been measured. The up-conversion of red radiation (650 nm) into UV (368 nm and 379 nm), blue (406.8 nm) and green (522 nm and 540 nm) emissions is observed for Er³⁺ ions in the sample. The up-conversion process involves a two-photon absorption for the violet, blue, and green emission bands. A three-photon process happens for another violet (379 nm) band.     

Anisotropic charge transport properties of chrysene derivatives as organic semiconductor: A computational study

We used density functional theory to calculate the angular resolution anisotropic charge mobility of the substituted chrysene molecules, viz, 4,10‐diphenoxychrysene (DPC), 4,10‐bis(phenylsulfanyl)chrysene (BPSC), and ethyl 8,9,12‐trimethoxychrysene‐6‐carboxylate (ETCC). The highest occupied molecular orbital–lowest unoccupied molecular orbital gap for DPC, BPSC, and ETCC was calculated to be 3.92, 3.83, and 3.81 eV, respectively, which inferred the compounds to be wide‐band‐gap semiconductors indicating that the compounds should have high stability in atmospheric conditions. The fact is also supported by electronic band‐structure calculation. In addition, higher electron affinity of studied compounds as compared with the bare chrysene molecule imparts enhancement of n‐type character in the compounds. The maximum hole ( ) and electron mobilities ( ) for DPC compound were found to be 0.739 cm²V^?1s^?1 and 0.319 cm²V^?1s^?1, respectively, at Φ = 0°. On the other hand, in the case of BPSC crystal, comparatively larger anisotropic electron mobility (0.709 cm²V^?1s^?1 at Φ = 0° and Φ = 179.90°) than the hole mobility (0.208 cm²V^?1s^?1 at Φ = 127.19° and Φ = 307.10°) was noted. Similarly, in ETCC, the parallel dimers were found to contribute maximum and of 0.052 and 0.102 cm²V^?1s^?1, respectively, at Φ = 0°. The substitution of ‐SPh in BPSC and ‐OCH₃ and ‐CO₂CH₂CH₃ in ETCC have relatively more impact on band reduction than ‐OPh in DPC, thus facilitating electron transport in BPSC and ETCC.     

Effect of Dichroic dye on dielectric properties of ferroelectric liquid crystals: A comparative study

In order to study the effect of mixing dye molecules in ferroelectric liquid crystals, we have investigated two ferroelectric liquid crystal samples CS1016 and Felix 17/000 along with their mixture with Anthraquinone dye. The measurements have been made in the frequency range 100 Hz-10 MHz, with the variation of temperature from 30 to 90 °C. The dielectric behaviour of dye mixed CS1016 is quite different from that of Felix 17/000. This different behaviour has been explained by determining other parameters like distribution parameter, dielectric strength and relaxation frequency, etc. The different nature shown by two different samples has also been explained by electro-optical measurements.     

Cation sitting in aromatic cages: ab initio computational studies on tetramethylammonium–(benzene)n (n=3–4) complexes

Quantum chemistry study was performed on interaction between tetramethylammonium (TMA) and aromatic cages by means of the MP2 method to show how TMA sits in an aromatic cage that is composed of benzenes. The MP2 calculations on TMA–(benzene)_n complexes demonstrate that the more the benzene molecules in the aromatic cage, the stronger the binding strength between the cage and TMA. In details, the structure of TMA–(benzene)_n (n = 1–4) complexes can be easily constructed by superimposing n TMA‐benzene complexes via TMA, and the binding energies of the TMA–(benzene)_n complexes are the sum of the n corresponding TMA‐benzene systems. For instance, the distances between the N of TMA and the plane of the benzene ring are 4.238, 4.252, 4.264 ,and 4.276 Å, respectively, for TMA–(benzene)_n (n = 1–4) complexes, and the BSSE corrected binding energies at MP2/6‐311++G** level are ?8.8, ?17.3, ?25.8 and ?34.3 kcal/mol, respectively, for TMA– (benzene)_n (n = 1–4) complexes. Thus, this study provides us useful information on how a cation interacts with an aromatic cage in terms of complex geometry and binding strength. Copyright © 2007 John Wiley & Sons, Ltd.     

A study of blast waveforms detected simultaneously by a microphone and a laser probe during laser ablation

We examine blast waves generated in air during irradiation of absorbing samples with Nd: YAG laser pulses of fluences exceeding the ablation threshold. Blast waves were detected simultaneously by a wideband microphone and a laser beam deflection probe. By a comparative analysis of both signals in the time and frequency domain we investigate characteristic features of their nonlinear waveform evolution. To explain the observed phenomena we employ the weak shock solution of the point explosion model.     

Ultrasonic assisted synthesis of two urea functionalized metal organic frameworks for phenol sensing: A comparative study

Two pillared metal-organic frameworks containing urea functional groups were synthesized by a sonochemical method and characterized by scanning electron microscopy, X-ray powder diffraction, IR spectroscopy and elemental analysis. The time of sonication and concentration of starting materials have been optimized to synthesize nanoparticles of TMU-31 and TMU-32. These two frameworks are interesting candidates for a comparative fluorescence study. Thus, their potential abilities for phenol sensing were investigated. This investigation revealed the prominent roles of hydrogen bond donating urea groups inside the pore cavity in the ability of these structures in phenol sensing.     

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.     

Premicellar and micelle formation behavior of aqueous anionic surfactants in the presence of triphenylmethane dyes: protonation of dye in ion pair micelles

The premicellar and micelle formation behaviors of four cationic triphenylmethane dyes, viz, Pararosaniline (RN), Crystal violet (CV), Ethyl violet (EV), and Malachite green (MG), in aqueous anionic surfactant solutions of sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS), and sodium dodecyl sulfonate (SDSN) have been studied by spectral and surface tension measurements. The study was carried out within a pH range where the dyes are stable in their quinoid forms. The dyes have been found to form dye–surfactant ion pairs (DSIPs) with the surfactants, at the surfactant concentrations well below their critical micelle concentration, CMC*. The DSIPs behave like nonionic surfactants and form an air–water interfacial monolayer. The DSIPs have a lower critical micelle concentration (CMC_IP), greater efficiency, and lower effectiveness than the corresponding pure surfactants. As the surfactant concentration is increased below the CMC*, the DSIPs start forming micelles of their own where the dye gets protonated and exists as a protonated dye–surfactant ion pair (PDSIP) in the ion pair micelles. As the concentration of the surfactant exceeds the CMC* of the pure surfactant, the protonation reverses gradually with the dye remaining in the micelles in solubilized form and the DSIPs in the air–water interfacial monolayer are replaced by pure surfactants. The distorted helical isomeric form (isomer B) of the dyes is favored in the PDSIPs. Copyright © 2009 John Wiley & Sons, Ltd.