CN Bond Lengths Research Articles

Experimental and theoretical calculation of pKa values of substituted-2,4,6-trinitrodiphenylamines

The pKa values of eighteen 2,4,6-trinitrodiphenylamine derivatives were determined experimentally from their UV–vis spectra and their values were also calculated using quantum chemical methods. The accuracy of the various levels of theory and basis sets were assessed using the solvation model based on density and conductor-like screening model. Linear correlation coefficients of the calculated pKa values are in the range 0.44 – 0.89, 0.11 – 0.90 and 0.43 – 0.90, when compared with those obtained experimentally, for the 6-311++G(d,p), 6-31+G(d,p) and 6-31G(d) basis sets respectively. Increasing the size of the basis set by adding polarization and diffuse functions increase the average errors in the calculations, for ωB97XD functional in acetonitrile. Such variation was not observed in other functionals. Furthermore, the mean signed errors (MSE) for calculations with semiempirical methods are highly comparable but with very poor linear correlation coefficients. The M06-2X functional, in combination with the 6-31+G(d,p), 6-311++G(d,p) and 6-31G(d) basis sets, gave a much better performance than the other functionals used in the present study. The effect of empirical dispersion in the PM6-DH + method was not significant, as the results are similar to those obtained with AM1 and PM7. A strong correlation was observed for the pKa values obtained experimentally with Hammett σ constants, CN bond lengths and charges.

Consequence of Proton Transfer and Hydrogen Bonding Interactions on the Molecular, Vibrational and Biological properties of the Novelly Synthesized Antibacterial Compound bis-(4-Dimethylaminopyridinium) bis-(3, 5-Dinitrobenzoate) monohydrate using DFT Study

In the present work, a proton transfer compound bis-(4-Dimethylaminopyridinium) bis-(3,5-Dinitrobenzoate) Monohydrate was synthesized and characterized by spectroscopic techniques with the aid of quantum chemical computations. Effect of hydrogen bonding on the molecule is studied from the geometrical parameters, interaction energies and vibrational spectra. The discrepancy in CN and CH bond length from the standard value, which further increases the electron density as evident from NBO analysis and also leads to a change in vibrational frequencies, is evidence of protonation and hyperconjucative effect, which is primarily responsible for the compound's bioactivity. The energy gap as per HOMO-LUMO calculations is 2.945 eV signifying that the molecule would be both stable and bioactive in nature. MEP plot and Fukui functions validate that the carboxylate and nitro group in 3, 5-dinitrobenzoate serve as hydrogen bond electron acceptor whereas the hydrogen atoms of pyridine ring serve as an electron donor. The antibacterial test also merely confirms DPDB's potent antibacterial activity against the bacterial strains. The compound DPDB inhibits the gram-negative bacterium Escherichia coli, which causes urinary tract infections, pneumonia, and meningitis, according to antibacterial testing.

Electronic states of nitromethane: Experimental and theoretical studies

A comprehensive spectroscopic study of the UV–VUV photoabsorption spectrum of nitromethane in the energy region 5.4–11.8 eV (43,500–95,000 cm−1) using synchrotron radiation is presented; the VUV absorption spectrum in the region > 9 eV being reported for the first time. The observed spectral features are assigned to various valence and Rydberg transitions, supported by quantum chemical calculations using the TDDFT method. The 6 eV region is dominated by a broad, intense absorption band peaking at ∼ 6.2 eV assigned to the π-π* valence transition, followed by rich Rydberg series converging to the first four ionization potentials of nitromethane. Theoretical calculations of orbital energies as well as Rydberg series analysis indicate that the third IP is located at 11.95 eV, in contrast to the earlier estimated value of 11.5 eV. Series of bands attributed to vibrational transitions accompanying the 3s (6a″), 3p(6a"), 3s(10a′) and 3s(5a″) Rydberg transitions are observed in the 60,000–73,000 cm−1 region and are tentatively assigned to progressions involving the NO2 in-plane rock and CH3 asymmetric deform modes. The liquid phase IR spectrum is revisited and assigned with the help of DFT calculations. A few new bands are observed and assigned to overtone and combination modes. Theoretically simulated potential energy curves of the first few excited singlet and triplet states with respect to the CN and NO bond lengths are useful in explaining some of the incompletely understood features of the photodissociation dynamics of nitromethane. It is found that direct dissociation in the Franck Condon region is a possible mechanism for the CH3NO + O channel, while singlet-triplet crossings play an important role in CN and NO bond scissions.

Iron tricarbonyl α-diimine complexes: Synthesis, characterization, and electronic structure based on X-ray crystal structures

A series of iron tricarbonyl α-diimine complexes, Fe(ArDABMe)(CO)3, were synthesized, in which the identity of the aryl substituent on the α-diimine ligand was varied (ArDABMe = Ar-NC(Me)-(Me)CNAr; 2a Ar = C6H5; 2b Ar = 3,5-(CH3)2C6H3; 2c Ar = 2,4,6-(CH3)3C6H2; 2d Ar = 3,5-Cl2C6H3), and the complexes were characterized by 1H and 13C NMR spectroscopy. The IR spectra of compounds 2a-d exhibit three carbonyl stretches between 2040 and 1950 cm−1, and all four compounds can be reduced by two electrons at potentials between −1.8 and −2.8 V vs. Cp2Fe/Cp2Fe+. The differences in νCO and reduction potentials are related to the differences in electron donating abilities of the α-diimine aryl substituents. The structures of 2a-d were determined by single crystal X-ray diffraction experiments; compounds 2a, b, and d have distorted square pyramidal structures, whereas, compound 2c is distorted trigonal bipyramidal. In order to assess the oxidation state of the α-diimine ligand in compounds 2a-d, we synthesized and crystallographically characterized a series of compounds that contain the neutral forms of the four α-diimine ligands. In compounds 2a-d, the average CN bond lengths are 1.332(1) Å and average backbone CC bond lengths are 1.403(2) Å, compared to 1.279(1) Å and 1.520(3) Å, respectively, in the neutral ligands. The lengthening of the CN bonds and shortening of the CC bonds are indicative of reduction of the α-diimine ligands. Therefore, compounds 2a-d are best described as containing Fe(I) centers bonded to radical anionic α-diimine ligands.

Design, structural investigations and antimicrobial activity of pyrazole nucleating copper and zinc complexes

The present study accounts for the construction of two novel complexes by the interaction of pyrazole nucleating ligand with Cu(II) (1) and Zn(II) (2) ions in 1:1 equivalent ratio, and their structural investigation by elemental analyses, FT-IR, NMR and thermal studies. Complex 1, additionally characterized by single crystal X-ray crystallography, reveals the coordination of the pyrazole nucleating ligand to the metal ions by the imine nitrogen, carbonyl oxygen and phenolic oxygen of the ligand and chloride ion. Furthermore, the coordination environment of the central atom adopts slightly distorted square-planar geometry with sum of interbond angles equal to 701.49°. The analysis of CN bond lengths shows that the double bond is localised within imine moiety and respective bonds shows considerable degree of delocalisation within pyrazole ring. The mixed basis set 6-311G(d) and LANL2DZ with B3LYP functional is applied for DFT calculation to determine the bonding insights into the structure of the complex. Natural Population Analysis (NPA) is also carried out to define the nature of the charge on copper atom in complex 1. In addition, Hirshfeld surface analysis is also carried out to know the various intermolecular interactions. The ligand and its complexes were evaluated against Pseudomonas aeruginosa, Escherichia coli, Shigella sonnei, Bacillus subtilis, Aspergillus niger, Aspergillus flavus, Fusarium oxysporum, Penicillium notatum microbial species, and showed significant effects on the tested microbes.

Use of 13C and 1H NMR to determine in detail the structures of the base-off vitamin B12 complexes dicyanocobinamide and dicyanocobalamin

Despite many attempts over more than sixty years, it has not been possible to produce single crystals of any cobalt cobinamides to determine their structure by X-ray crystallography. This paper describes the use of 13C and 1H NMR and comparison with known X-ray crystal structures of similar molecules to determine the structure of cobinamides. The structure of dicyanocobinamide, the simplest cobinamide, in methanol solution, is described by comparison with dicyanocobester. The delocalised system of dicyanocobinamide, which is nearly planar, and the rest of the corrin ring, except for C8, are very similar to those of dicyanocobester. The environment of the axial CN− ligands, including the Co–CN bond lengths and the NC–Co–CN bond angle is similar to that of dicyanocobester and the α-CN− ligand is bent away from the C20 methyl group. The structure of the corrin ligand and coordination sphere of base-off dicyanocobalamin, which occurs only in solution, is similar to that of dicyanocobinamide.

The selenocyanate dimer radical anion in water: Transient Raman spectra, structure, and reaction dynamics.

The selenocyanate dimer radical anion (SeCN)2 •-, prepared by electron pulse irradiation of selenocyanate anion (SeCN)- in water, has been examined by transient absorption, time-resolved Raman spectra, and range-separated hybrid density functional (ωB97x and LC-ωPBE) theory. The Raman spectrum, excited in resonance with the 450 nm (λmax) absorption of the radical, is dominated by a very strong band at 140.5 cm-1, associated with the Se-Se stretching vibration, its overtones and combinations. A striking feature of the (SeCN)2 •- Raman spectrum is the relative sharpness of the 140.5 cm-1 band compared to the S-S band at 220 cm-1 in thiocyanate radical anion (SCN)2 •-, the difference of which is explained in terms of a time-averaged site effect. Calculations, which reproduce experimental frequencies fairly well, predict a molecular geometry with the SeSe bond length of 2.917 (±0.04) Å, the SeC bond length of 1.819 (±0.004) Å, and the CN bond length of 1.155 (±0.002) Å. An anharmonicity of 0.44 cm-1 has been determined for the 140.5 cm-1 Se-Se vibration which led to a dissociation energy of ∼1.4 eV for the SeSe bond, using the Morse potential in a diatomic approximation. This value, estimated for the radical confined in a solvent cage, compares well with the calculated gas-phase energy, 1.32 ± 0.04 eV, required for the radical to dissociate into (SeCN)• and (SeCN)- fragments. The enthalpy of dissociation in water has been measured (0.36 eV) and compared with the value estimated by accounting for the solvent dielectric effects in structural calculations.

Adsorption characteristics and degradation mechanism of metronidazole on the surface of photocatalyst TiO2: A theoretical study

In this paper, the adsorption and degradation mechanism of metronidazole on TiO2 (101) and (001) surfaces was elucidated at DFT level. The adsorption stability of metronidazole on the surface of anatase was studied under the condition of vacuum and neutral aqueous solvent respectively, and the most stable adsorption configuration was optimized theoretically. It was found that metronidazole could be adsorbed on the surface of TiO2 under both conditions. The hydrogen bond generated by the adsorption process can enhance the stability of the adsorption structure. The surface adsorption made the CN bond length of metronidazole longer, which could facilitate the reaction of open-loop degradation. The mechanism of ring-opening degradation of metronidazole on two surfaces of TiO2 was also studied. It was found that the activation energy of the degradation reaction of metronidazole on the crystal plane of TiO2 was decreased under the condition of water solvent, which indicated that the solvent condition could promote the degradation of metronidazole. The utilization efficiency of different crystal planes of TiO2 in the visible light and predicted the photocatalysis were achieved. The study found that TiO2 (101) crystal plane catalytic degradation of metronidazole has high visible light utilization rate, explaining the experimental results.

X-ray structures, solid state periodic DFT modeling and vibrational study of alkylenediammonium hexachlorostannates compounds NH3(CH2)nNH3SnCl6 (n = 3, 4, 5)

Combined experimental (X-ray, IR and Raman) and theoretical (periodic DFT/PAW-PW91) studies have been performed for thorough understanding of the structure, hydrogen bonding and vibrational properties for three alkylenediammonium hexachlorostannates with the general formula: [NH3(CH2)nNH3]SnCl6 (n = 3, 4, 5). X-ray diffraction analysis indicated two structural systems: orthorhombic when n is odd (n = 3, 5), with space group Pnma (Z = 4) for [NH3(CH2)3NH3]SnCl6 and Pbca (Z = 8) for [NH3(CH2)5NH3]SnCl6 and monoclinic when n is even with space group C2/m (Z = 2) for [NH3(CH2)4NH3]SnCl6. The V/Z ratio variation (cell volume/number of motif per cell) as a function of the CH2 groups' number (n = 2–5) in H3N(CH2)nNH3SnCl6 compounds were discussed. Periodic DFT modeling was applied to specify: 1) the (C)C(-C) atom (observed experimentally in two general positions with an occupation of 50%), and 2) the hydrogen atoms in [NH3(CH2)3NH3]SnCl6 and [NH3(CH2)4NH3]SnCl6. The measured Infrared and Raman spectra of all the three compounds were interpreted by vibrational frequency calculations of solid state models and factor-group analysis. The CN bond lengths as well as the υ(CN) and υ1(υsSn-Cl) stretching modes were used for estimation of the relative hydrogen bonding strength in the studied series of alkylenediammonium hexachlorostannate. The strongest hydrogen bonding and packing effect were predicted for [NH3(CH2)3NH3]SnCl6 and they become weaker with increase of the CH2 group number (n).

First principle study of electronic structures and optical absorption properties of O and S doped graphite phase carbon nitride (g-C3N4)6 quantum dots

Graphite phase carbon nitride (g-C3N4) quantum dots have received much attention due to its good stability, water solubility, biological compatibility, non-toxicity as well as strong fluorescence characteristics. In order to enhance the light absorption and improve photocatalytic activities of the g-C3N4 quantum dots, theoretical studies are carried out on the O and S atoms doped (g-C3N4)6 quantum dots. First-principles calculations based on the density functional theory and time dependent density functional theory are performed to investigate the geometries, electronic structures and ultraviolet visible absorption spectra of O and S atoms doped (g-C3N4)6 quantum dots. The results show that the highest electron occupied molecular orbital-the lowest electron unoccupied molecular orbital (HOMO-LUMO) energy gap of doped (g-C3N4)6 quantum dots is significantly reduced though the CN bond lengths closely related to the impurities only change slightly. The calculated formation energies indicate that the O-doped (g-C3N4)6 quantum dots are more stable, and the O atom tends to substitute for N atom at the N3-site, while the S atoms prefer to substitute for N atom at the N8-site. The simulated spectra indicate that the doping of O and S in (g-C3N4)6 could improve the light absorption. Not only the absorption peaks are extended from the UV to the infrared region (e.g. 200-1600 nm), but also the corresponding absorption intensities are enhanced significantly by doping the O or S atoms with the appropriate concentration. The increase of proper impurity concentration will lead to a pronounced red shift in light absorption. The effect of doping site on the optical absorption property of (g-C3N4)6 quantum dots shows that the absorption intensity is mainly affected in the visible range, however, besides the influence on the absorption intensity, the light absorptions of some structures are also affected beyond 800 nm. Overall, the O atoms and S atoms have a substantially similar effect on the light absorption of the (g-C3N4)6 quantum dots, while the effects of these impurity atoms are different in the long wavelength region. Oxygen doping is better than sulfur doping in the absorption of (g-C3N4)6 quantum dots by comparing the doping of O and S. These first-principles studies give us a method to effectively improve the light absorption of g-C3N4 quantum dots, and could provide a theoretical reference for tuning its electronic optical properties and applications.

Synthesis, characterisation and antimicrobial activity of new palladium and nickel complexes containing Schiff bases

New Schiff base ligands were synthesized by condensation of 2-(3,4-dimethoxyphenyl)ethanamine with 2-hydroxy benzaldehyde (L1H) and 2′-hydroxy acetophenone (L2H) respectively. Reaction of L1H or L2H with Na2PdCl4 or NiCl2·6H2O in 2:1 ratio obtained four new coordination complexes [M(L1–2)2] (where M=Pd(II); 1 and 2 and M=Ni(II); 3 and 4). Both the ligands and four complexes were characterised by elemental analysis, FT-IR and UV–Vis, spectroscopy. L1H, L2H, 1 and 2 were also characterised by 1H and 13C{1H} NMR spectroscopy. The molecular structures of 1 and 3 were determined by single crystal X-ray diffraction. The spectroscopic and crystal structure data showed that the ligands coordinated to M(II) ion in a bidentate monoanionic (O−, N) fashion. The PdO and PdN bond lengths in 1 are 1.984(11) and 2.020(12)Å in 3 the NiO and NiN bond lengths are 1.8222(13) and 1.9262(15)Å respectively. The CN bond length in 3 found 1.290(2)Å which was shorter than 1.310(19)Å in 1. The bond angles provided square planar geometry around Pd(II) and Ni(II) in both 1 and 3. There exists CH⋯O type (2.50–2.52Å) intermolecular hydrogen bonding in both 1 and 3 resulting in supramolecular structures. The antimicrobial activity of new Schiff base ligands and their Pd(II) and Ni(II) complexes against pathogenic microbial strains by agar well diffusion method was conducted. All the ligands and complexes showed significant antibacterial and antifungal activities. The bacterial and fungi growth inhibition activity of ligands has been increased on complexation as well as among complexes palladium complexes were found better antibacterial and antifungal agents than the nickel complexes of corresponding ligands. Ligand L1H and the complex 2 showed highest antibacterial activity against Pseudomonas desmolyticum and highest antifungal activity against Candida albicans.

Ab initio theoretical reinvestigation of the ground and excited state properties of silylated coumarins: Good candidates for solid state dye lasers and dye-sensitized solar cells

We present ab initio theoretical calculations of various properties of the ground and excited states of basic coumarin (1) and its derivatives: 4-methylcoumarin (2), 7-aminocoumarin (3), 7-amino-4-methylcoumarin or coumarin 120 (4), 4-trifluoromethylcoumarin (5), 7-amino-4-trifluoromethylcoumarin or coumarin 151 (6), silylated coumarin 120 (7) and silylated coumarin 151 (8). We calculate the following: (i) ground and excited state dipole moments (ii) energies and locations of HOMOs and LUMOs (iii) SCF total energies of ground state (iv) excitation energies with oscillator strengths for first six excited states (v) CO and CN bond lengths in ground and excited states (vi) ground state thermodynamic and electronic properties. The ground and excited state properties of coumarins 1–8 are obtained within the framework of density functional theory using B3LYP and long-range-corrected (LRC) ωB97X-D functionals with 6–31G(d,p) basis set. A detailed comparative analysis of different photo physical and electronic properties of silylated and unsilylated coumarins is made. On the basis of theoretical results we find many interesting features of silylation process and we can conclude that silylation will result in better long-term photo and thermodynamic stability compared to its unsilylated counterpart due to increase in the values of thermodynamic parameters like SCF total energy, G0 and H0, etc. Therefore, silylated molecules may become good candidates for solid state dye lasers and dye sensitized solar cells. In contrast, we find that both the functional B3LYP and LRC-ωB97X-D predict nearly the same results for electronic, thermodynamic and photo physical properties of studied coumarins 1–8 in their ground states but B3LYP hybrid functional severely overestimates excited state dipole moments, underestimates vertical excitation energies, oscillator strengths, CO and CN bond lengths of studied coumarins. On the basis of our theoretical results we conclude that LRC-ωB97X-D functional must be used for prediction of excited state properties of a molecule.

Multinuclear NMR Study of Zinc Dicyanide

Abstract The isotropic negative expansion of Zn(CN)2 has been linked to a temperature induced increase in off-axis tilting of the C–N bond direction and an increase in CN-bond length. However, the bond length could be determined only indirectly based on pair-distribution function analysis and was found to be surprisingly large. Here we study Zn(CN)2 by nuclear magnetic resonance spectroscopy and first principles calculations. By using samples enriched in 13 C and 15 N the dipole coupling between carbon and nitrogen is determined, and from this an upper bound on the C–N bond length of 1.19 ± 0.01 Å is derived. This quantity agrees with earlier determinations based on diffraction but is shorter than estimates based on pair distribution function analysis. The relation of this estimate to possible dynamics in the sample is discussed. Finally, 67 Zn NMR is used together with first principles calculations to assess disorder in the material.

FT-IR, FT-Raman and computational study of (E)-N-carbamimidoyl-4-((4-methoxybenzylidene)amino)benzenesulfonamide

The FT-IR and FT-Raman spectra of (E)-N-carbamimidoyl-4-((4-methoxybenzylidene)amino)benzenesulfonamide were recorded and analyzed. Geometry and harmonic vibrational wavenumbers were calculated theoretically using Gaussian 03 set of quantum chemistry codes. Calculations were performed at the Hartree–Fock (HF) and density functional theory (DFT) levels of theory. The calculated wavenumbers (B3LYP) agree well with the observed wavenumbers. Potential energy distribution is done using GAR2PED program. The red shift of the NH stretching bands in the infrared spectrum from the computed wavenumber indicates the weakening of the NH bond. The calculated first hyperpolarizability is comparable with the reported value of similar derivative and may be an attractive object for further studies of nonlinear optics. The variations in the CN bond lengths of the title molecule suggest an extended π-electron delocalization over the sulfaguanidine moiety which is responsible for the nonlinearity of the molecule. The geometrical parameters of the title compound are in agreement with that of reported similar derivatives.

Substituent effects in 1,4-disubstituted benzene and cyclohexadiene: Olefinic vs aromatic electron shift pathway of the substituent effect

Substituent effects in 1-X-4-Y-substituted benzene and cyclohexadiene derivatives were studied for X=OH or NO2, and Y=BH2, B(OH)2, CCH, CH3, CHO, Cl, CN, COCH3, COCl, CONH2, COOCH3, COOH, F, H, NH2, N(CH3)2, NO, NO2, OCH3, OH. All systems were optimized at the B3LYP/6-311+G∗∗ DFT level of theory and the resulting data of the optimized systems were used to estimate various characteristics of the interactions between the fixed (the same in a given series of calculations) groups X (OH or NO2) and the substituents. The following characteristics were used: substituent effect stabilization energy (SESE), harmonic oscillator model of aromaticity (HOMA) calculated for three CC bonds (1–4 bond aromatic or olefinic pathway in the rings), occupations of 2pz orbitals at C1C2C3C4 named pEDA, changes in CN or CO bond lengths, NPA charges at OH and NO2, delocalization index (DI) between atoms C1 and C4, magnetic susceptibility. In all cases (except the last one) sensitivity of the pathway via C1C2C3C4 bonds in cyclohexadiene derivatives was significantly greater than in the case of the pathway via aromatic system.

Nonadiabatic Hybrid Quantum and Molecular Mechanic Simulations of Azobenzene Photoswitching in Bulk Liquid Environment

A nonadiabatic hybrid quantum and molecular mechanical (na-QM/MM) molecular dynamics scheme has been implemented recently combining the nonadiabatic Car-Parrinello molecular dynamics method by Doltsinis and Marx [Phys. Rev. Lett. 2002, 88, 166402] with the QM/MM coupling approach by Laio et al. [J. Chem. Phys. 2002, 116, 6941]. Here an extensive validation of the underlying, density functional theory based, electronic structure methods by comparison to CASPT2 ab initio data is presented for the case of azobenzene. The "on the fly" na-QM/MM method is then applied to study Z-->E and E-->Z photoisomerization of azobenzene in a bulk liquid environment. The isomerization mechanism is found to be a pedal motion of the central CN horizontal lineNC group in both cases. While the Z-->E reaction is barely affected by the environment, E-->Z photoisomerization is slowed down considerably in the liquid compared to the gas phase. This effect is due to the fact that reorientation of the phenyl rings is significantly hindered in the liquid by steric nearest neighbor interactions. Nonradiative decay is found to be substantially faster for Z-AB (subpicosecond regime) than for E-AB (picosecond regime). The main molecular motions responsible for nonadiabatic coupling have been identified as the oscillations in the NN and CN bond lengths, the CNN bond angles, and the CNNC dihedral angle.

EXAFS and XANES simulations of Fe/Co hexacyanoferrate spectra by GNXAS and MXAN

In the present paper Full Multiple Scattering (FMS) theory has been applied to analyse the cobalt hexacyanoferrate XANES spectra. The use of the MXAN program has permitted to calculate the edge spectra and to perform a fitting procedure with the experimental data, obtaining a set of structural parameters. A previously reported EXAFS analysis (which includes terms up to four-body MS calculations) was performed via the GNXAS package, by a Multiple Edge approach of both Fe/Co K-edges and Fe/Co/Ni K-edges, and using the same structural parameters for all edges. The XANES data of Fe and Co K-edges are independently analysed here. An excellent reproduction of the XANES spectra, and a good agreement with the previous EXAFS results is obtained. The CN bond length using EXAFS has been determined with a statistical error of few thousandths of Å, whereas structural parameter using MXAN are probed within a 0.01–0.03 Å accuracy.

FT‐IR and FT‐Raman spectra and ab initio calculations of 3‐{[(2‐hydroxyphenyl) methylene]amino}‐2‐phenylquinazolin‐4(3H)‐one

AbstractFourier transform infrared (FT‐IR) and Fourier transform (FT) Raman spectra of 3‐{[(2‐hydroxyphenyl)methylene]amino}‐2‐phenylquinazolin‐4(3H)‐one were recorded and analyzed. The vibrational wavenumbers of the title compound were computed using HF/6‐31G* and 6‐311G* basis sets and compared with experimental data. The assignments of the normal modes are done by potential energy distribution (PED)calculations. The prepared compound was identified by nuclear magnetic resonance (NMR) and mass spectra. Optimized geometrical parameters of the title compound are in agreement with reported structures. Shortening of CN bond lengths reveal the effect of resonance. The simultaneous IR and Raman activations of the CO stretching mode shows a charge transfer interaction through a π‐conjugated path. The first hyperpolarizability, infrared intensities and Raman activities are reported. The phenyl CC stretching modes are equally active as strong bands in both IR and Raman spectra, which are responsible for hyperpolarizability enhancement leading to nonlinear optical activity. Copyright © 2009 John Wiley & Sons, Ltd.

Ultrafast dynamics and photochemistry of π–π* excited trans‐azobenzene—a comprehensive analysis of resonance Raman intensities

AbstractAzobenzene and its derivatives have widely been recognized as systems with potential applications such as optical switching elements, and the mechanism of trans‐cis photoisomerization, which is the basis for all these applications, has long been sought. The long‐standing controversy on the relaxation mechanism of π–π* (S2) excited trans‐azobenzene (TAB) is addressed in this paper. The role of S1S2 intersection and the possible involvement of a third state in the S2 photochemistry are investigated. The excited state structure and dynamics of TAB are extracted by modeling the Raman excitation profiles (REPs) of the S1 and S2 states and the absorption spectrum of TAB by Heller's time‐dependent formalism. The REPs of S2 are modeled in the single resonant state approximation by explicitly including the eight most Franck–Condon (FC) active modes. The obtained NN and CN bond lengths of S2 and the intial dynamics in these coordinates following photoexcitation to S2 are in agreement with recent theoretical calculations. The structural parameters of S1 are obtained by exploiting the nature of interference in the REPs of S1. From these parameters a three‐mode–two‐state vibronic coupling model, based on harmonic diabatic potentials and linear coupling, is formulated to study the S2S1 internal conversion dynamics. The results indicate that the S1S2 intersection is not directly accessible within electronic dephasing time of S2 to cause significant population decay from S2 to S1. The current conception of π–π* relaxation mechanisms in TAB is reviewed and revised on the basis of our observations and also from recently reported results of time‐resolved and theoretical studies. The role of a third state (S3), which appears to be an integral part of in the relaxation mechanism of S2, is pointed out and the feasibility of two competing relaxation pathways for S2 state is identified. One is the direct rotationless S2S1(C2h) internal conversion and the other is S2S3 internal conversion along rotational pathway followed by a branching of the S3 population to S0 and S1. Copyright © 2008 John Wiley & Sons, Ltd.

Structure of Fe/Co/Ni Hexacyanoferrate As Probed by Multiple Edge X-ray Absorption Spectroscopy

The structural parameters in selected cobalt and mixed cobalt/nickel hexacyanoferrates have been determined by X-ray absorption spectroscopy. The presence of two or three metals in the sample requires the use of a highly efficient multiple edge analysis. The typical structure of mixed hexacyanoferrates coupled with a suitable data analysis program, GNXAS, allow us to determine structural parameters considering a very high number of experimental points. The first data analysis of three contiguous edges (Fe, Co, and Ni K-edges), the structural parameters of which are entirely correlated, is presented. The advantages and limitations of the multiple edge approach are underlined and placed in the context of the previous studies. The CN bond length has been determined with a statistical error of few thousandths of an angstrom.