Theoretical studies of the structural,electronic and optical properties of carbazole‐based compounds

Carbazole derivatives have drawn increasing attention recently in organic electronic device applications because of their particular optoelectronic properties. An in‐depth theoretical investigation was elaborated in this paper to reveal the molecular structures, optoelectronic properties, and the structure‐property relationships of different carbazole‐linked functional groups. The geometric and electronic structures in ground and the mobility for the hole and electron are both calculated by density functional theory method. The excited‐state geometries of these compounds were obtained through Single‐excitation Configuration Interaction method, and time‐dependent density functional theory calculation results described the absorption and emission spectra properties, respectively. Some conclusions are as follows: (1) enlarging the π‐conjugated area, the corresponding spectra red shifted markedly; (2) by introducing the electron‐donor such as carbazole, the spectra blue shifted slightly; (3) compared with compound 1, the spectra for these compounds are hardly influenced by introducing an electron‐acceptor or heterocyclic substitution. On all accounts, these compounds are interesting optoelectronic functional materials. On the basis of their structural modifiability, the arylamine derivatives substituted carbazole compounds have great potential in the applications of organic light‐emitting diodes, organic solar cells, and sensors. Copyright © 2011 John Wiley & Sons, Ltd.     

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.     

Computational design of tetrazolone‐based high‐energy density energetic materials: Property prediction and decomposition mechanism

The density functional theory methods are used to design a series of new highly energetic tetrazolone‐based molecules by the combination of the linked tetrazolone framework and versatile substitutes. The molecular and electronic structures, physicochemical, and energetic properties were analyzed and predicted. The decomposition mechanisms were computationally simulated, and 3 potential decomposition channels were proposed. These newly designed tetrazolone‐based compounds show high densities (up to 2.08 g/cm³) and highly positive heats of formation (407.0‐1377.9 kJ/mol) due to all right content of nitrogen and oxygen. Most of them exhibit good detonation velocity (8.31‐9.62 km/s) and detonation pressure (32.40‐43.86 GPa), and some are comparative to excellent explosive CL‐20. Results show that compounds 6 , 10 , 11 , 12 , 15 , 16 , 17 , 22 , 23 , and 24 own superior detonation performance than widely used explosive HMX and may be promising candidates of green high‐performance energetic materials.     

Mechanistic insights into C‐C cross coupling activities of Pd/Ni‐doped heterofullerenes

Mechanistic insights into Heck and Suzuki‐Miyaura cross coupling reactions with C₅₉M (M = Pd/Ni) catalysts were developed. Density functional theory was used for the analysis of all the intermediates and transition states possible during C‐C cross coupling reactions over the catalysts under study. Oxidative addition, a step common to both Heck and Suzuki‐Miyaura cross coupling reactions, was observed to proceed with smaller activation barriers over C₅₉Pd. Heck coupling of iodobenzene with styrene was observed to proceed via oxidative addition, migratory insertion, and reductive elimination steps. The free energy barriers for oxidative addition, migratory insertion, and reductive elimination steps were 14.8, 11.6, and 4.8 kcal/mol, respectively, over C₅₉Pd, and 17.4, 79.3, and 17.4 kcal/mol, respectively, over C₅₉Ni, indicating oxidative addition and migratory insertion to be the rate‐determining steps over C₅₉Pd and C₅₉Ni, respectively. Similarly for Suzuki‐Miyaura coupling reaction, activation barriers for oxidative addition, transmetalation, and reductive elimination steps were 14.8, 52.4, and 7.9 kcal/mol, respectively, over C₅₉Pd, and 17.4, 64.7, and 60.2 kcal/mol, respectively, over C₅₉Ni, indicating transmetalation step to be the rate‐determining step over both the heterofullerenes.     

Theoretical investigation of two‐photon absorption and fluorescence properties of cypridina luciferin‐based derivatives: 2,3,5‐trisubstituted pyrazine compounds

Two‐photon fluorescent probe materials are significant for achieving observation of living phenomena in entire organs and tissues. To explore new materials with high fluorescence and large two‐photon absorption (TPA) cross section, a series of 2,3,5‐trisubstituted pyrazine derivatives were designed. Their equilibrium geometries, one‐photon absorption, TPA, and luminescence properties have been studied by using density functional theory (DFT), time‐dependent DFT, and Zerner's intermediate neglect of differential overlap program. The results show that the introduction of styrene groups to 2,3,5‐trisubstituted pyrazine derivatives can efficiently increase the conjugated effect and enhance the TPA activity. Moreover, the luminescence properties of 2,3,5‐trisubstituted pyrazine derivatives were compared, and the effect of three substituents on the fluorescence of trisubstituted pyrazine derivatives was analyzed by means of different contribution of the basis functions localized on pyrazine fragment into the highest occupied molecular orbital and lowest unoccupied molecular orbital. The oscillator strengths in the excited state (?_em) for the pyrazine derivatives substituted by styryl are larger than that of other derivatives with acetylamino and indole groups substituted at 2‐site and 5‐site of the pyrazine core, and the ?_em of 3‐indolyl pyrazine derivatives is larger than that of 3‐styrene pyrazine derivatives. It suggests that the styrene group has a great influence on the luminescence property. In addition, the indole group substituted at 3‐site of the pyrazine derivatives can also promote the fluorescence property. Copyright © 2013 John Wiley & Sons, Ltd.     

Analysis of vibrational spectra of 2‐fluoro‐6‐nitrotoluene based on density functional theory calculations

The conformational behavior and structural stability of 2‐fluoro‐6‐nitrotoluene (FNT) were investigated by utilizing density functional theory (DFT) with the standard B3LYP/6‐311 + G** method and basis set combinations. The vibrational wavenumbers of FNT were computed at DFT levels and complete vibrational assignments were made on the basis of normal coordinate calculations. Normal coordinate analysis (NCA) has been carried out to support the vibrational analysis. The results were compared with the experimental values. The observed Fourier transform infrared (FTIR) and Fourier transform (FT) Raman vibrational wavenumbers were analyzed and compared with the theoretically predicted vibrational spectra. The results of vibrational spectra of FNT were also compared with the vibrational spectra of some toluene derivatives. The assignments of bands to various normal modes of the molecules were also carried out. Copyright © 2008 John Wiley & Sons, Ltd.     

Computational studies on two novel energetic nitrogen‐rich compounds based on tetrazolone

Two novel energetic nitrogen‐rich compounds 1,4‐diaminotetrazol‐5‐one ( DATO ) and 1,4‐dinitrotetrazol‐5‐one ( DNTO ) were proposed first and studied by quantum chemistry method with B3LYP/6‐31G* level of theory. The optimized geometry, IR predicted spectrum and thermochemical parameters, frontier molecular orbitals and molecular electrostatic potential were calculated for inspecting the electronic structure, molecular stability and chemical reactivity. The important macroscopic properties including density, enthalpy of formation, detonation parameters and impact sensitivity have been predicted as well. As a result, two designed compounds DATO and DNTO possess positive enthalpy of formation (395.79 and 342.77 kJ/mol), impressive detonation parameters (D = 8.80 km/s, P = 33.69 GPa; D = 8.89 km/s, P = 34.98 GPa) superior to the remarkable explosive RDX, acceptable sensitivities and might be promising candidates of energetic materials. Copyright © 2015 John Wiley & Sons, Ltd.     

吡唑联吡咯类化合物结构和活性的密度泛函理论研究

采用密度泛函理论中的广义梯度近似(DFT/GGA)方法,在PW91/DNP水平上研究了10种吡唑联吡咯类化合物的结构、化学活性和前线轨道.结果表明:此类化合物的能隙Eg大部分都在3.50~4.20e V之间,其中在吡咯环3位取代三氟甲基,或是在吡咯环5位取代4-甲苯氧基,化合物的能隙变宽.通过比较还发现,吡唑联吡咯类化合物对水稻纹枯菌(Rhizoctonia solani bacteria)的杀菌活性比2,3-二取代喹唑啉-4(3H)-酮化合物和哌啶并噻吩并嘧啶酮衍生物对水稻纹枯菌的杀菌活性都差.     

CuCl催化下苯炔与环己烯乙炔偶联反应机理的理论研究

利用密度泛函理论(DFT)研究了Cu Cl催化下苯炔与环己烯乙炔偶联反应的微观反应机理.在B3LYP/6-31+G*基组水平上(Cu采用了赝势基组Lan L2DZ)优化了反应过程中所有化合物的几何构型并计算了频率,通过能量、频率和振动方式确定了中间体和过渡态的真实性.此外,在同等基组水平上还运用了分子中的原子理论讨论了成键临界点的电荷密度的变化,运用了自然键轨道理论讨论了键的性质与轨道间的相互作用.为了提高计算精度,在6-311+G*基组水平上计算了反应机理中所有物质在气相及溶剂化下的单点能,得到与6-31+G*基组计算相同的结论.结论表明Cu Cl对苯炔与1-乙炔基环己烯偶联反应起到了有效的催化作用,且计算所得结论与实验结果相符合.     

The application of a new approach based on organic homo‐rank compounds and homologous compounds to the structure–property relationship study of mono‐substituted alkanes

The two conceptual systems of organic homologous compounds and homo‐rank compounds give insight into the influence of structures on the properties of mono‐substituted alkanes X_i–(CH₂)_j–H from the transverse (change of repeating unit number j of CH₂) and longitudinal (change of functional group X_i) perspectives, respectively. This paper aims to combine the organic homo‐rank compounds approach together with the homologous compounds approach to explore the property change rules of mono‐substituted alkanes involving various substituents. Firstly, based on the concept of organic homologous compounds, the properties of mono‐substituted straight‐chain alkane homologues were linearly correlated to the two‐thirds power of the number of carbon atoms (N^2/3) in alkyl, and regression equations such as Q = A + BN^2/3 were obtained. The regression coefficients A and B vary with different substituents X_i, so coefficients A and B were employed to characterize the structural information of substituent X_i. The structural features of alkyls (–(CH₂)_j–H, that is, –C_jH_2j+1) were described by the polarizability effect index (PEI_(R)) and vertex degree–distance index (VDI). Then based on four parameters A, B, PEI_(R), and VDI, quantitative structure–property relationship models were built for the boiling points (Bp) and refractive indexes (n_D) of each mono‐substituted alkane homo‐rank series, where j = 3–10 and the substituents X_i involve F, Cl, Br, I, NO₂, CN, NH₂, COOH, CHO, OH, SH, and NC. Good results indicate that the combination of an organic homo‐rank compounds method and a homologous compounds method has exhibited obvious advantages over traditional methods in the quantitative structure–property relationship study of mono‐substituted alkanes concerning various substituents. Copyright © 2015 John Wiley & Sons, Ltd.     

Inelastic electron lifetimes in simple metals: Influence of spin–orbit coupling

Inelastic single‐particle lifetimes due to electron–electron Coulomb interaction are computed ab‐initio for aluminium, silver, gold and copper using an all‐electron density‐functional calculation and a parameter‐free evaluation of the dielectric function. The novel feature is the inclusion of spin– orbit coupling in the wave functions. We show that, even in light metals, spin–orbit interaction is important for the calculation of inelastic lifetimes because it influences the scattering matrix elements. The importance of spin mixing on the lifetimes in aluminium is examined. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Short‐time photodecay dynamics of meso‐tetra(p‐hydroxyphenyl)porphine in the condensed phase explored via resonance Raman spectroscopy and density functional theory calculation

Resonance Raman (RR) spectra of free‐base meso‐tetra(p‐hydroxyphenyl)porphine(THPP) were obtained with 397.9, 416 and 514 nm excitation wavelengths, and density functional calculations were carried out to help the elucidation of the photorelaxation dynamics of Soret (B_x and B_y bands) electronic transitions and the RR spectra of THPP. The RR spectrum indicates that the Franck–Condon (FC) region photorelaxation dynamics for the S₀ → S₅ excited electronic state is predominantly along the totally symmetric C_m phC stretching and the C_βC_β stretchingand simultaneously along the asymmetric (C_mC_α)as stretching, ν(phC  C)asstretching, δ(NH)s and γ(C_βH) vibrational relaxation processes, while that for S₀ → S₄ electronic state is predominantly along the C_m phC stretching and pyrrole breathing. The excited‐state structural dynamics of THPP determined from the RR spectra shows that internal conversion (IC) B_y → B_x electronic relaxation occurs in tens of femtoseconds, and the short‐time dynamics is interpreted using the time‐dependent wave packet theory and Herzberg–Teller (vibronic coupling) contributions. Copyright © 2010 John Wiley & Sons, Ltd.     

Density functional theory study of the bis‐3‐benzo‐crown ethers and their complexes with alkali metal cations Na+, K+, Rb+ and Cs+

The binding interactions of bis‐3‐benzo‐15‐crown‐5 ethers and bis‐3‐benzo‐18‐crown‐6 ethers (neutral hosts) with a series of alkali metal cations Na⁺, K⁺, Rb⁺ and Cs⁺ (charged guests) were investigated using quantum chemical density functional theory. Different optimized structures, binding energies and various thermodynamic parameters of free crown ethers and their metal cation complexes were obtained based on the Becke, three‐parameter, Lee–Yang–Parr functional using mixed basis set (C, H, O, Na⁺ and K⁺ using 6‐31 g, and the heavier cation Rb⁺ and Cs⁺ using effective core potentials). Natural bond orbital analysis is conducted on the optimized geometric structures. The main types of driving force host–guest interactions are investigated. The electron donating O offers a lone pair of electrons to the contacting LP* (1‐center valence antibond lone pair) orbitals of metal cations. The bis‐3‐benzocrown ethers are assumed to have sandwich‐like conformations, considering the binding energies to gauge the exact interactions with alkali cations. It is found that there are two different types of complexes: one is a tight ion pair and the other is a separated ion pair. Copyright © 2011 John Wiley & Sons, Ltd.     

Density functional theory study and vibrational analysis of FT‐IR and FT‐Raman spectra of N‐hydroxyphthalimide

The Fourier transform infrared (FT‐IR) spectrum of N‐hydroxyphthalimide has been recorded in the range of 4000–400 cm⁻¹, and the Fourier transform Raman (FT‐Raman) spectrum of N‐hydroxyphthalimide has been recorded in the range of 4000–50 cm⁻¹. With the hope of providing more and effective information on the fundamental vibrations, the Density Functional Theory (DFT)‐Becke3‐Lee‐Yang‐Parr (B3LYP) level with 6‐31G* basis set has been employed in quantum chemical analysis, and normal coordinate analysis has been performed on N‐hydroxyphthalimide by assuming C_s symmetry. The computational wavenumbers are in good agreement with the observed results. The theoretical spectra obtained along with intensity data agree well with the observed spectra. Copyright © 2009 John Wiley & Sons, Ltd.     

Solvent effects on guanidinium‐anion interactions and the problem of guanidinium Y‐aromaticity

We have calculated the complexes formed by guanidine/guanidinium and HCl/Cl^?, HNO₃/NO₃^? and H₂SO₄/HSO₄^? both in the gas and aqueous Polarizable Continuum Model (PCM) phase to understand the effect that solvation has on their interaction energies. In the gas phase, the cation–anion complexes are much more stable than the rest; however, when PCM‐water is considered, this energetic difference is not as large due to the extra stabilization that the ions suffer when in aqueous solution. All the complexes were analyzed in terms of their AIM and NBO properties. In all cases, water solvation seems to “dampen” those properties observed in the gas phase. The values of Nucleus Independent Chemical Shift (NICS)(1) and NICS(2) indicate a huge influence of the proximity of the carbon atom for short distances; thus, the 3D NICS values on the van der Waal isosurfaces have been used to evaluate the possible Y‐aromaticity of the guanidinium system. The isosurface in this system is more similar to cyclohexane than to benzene as indication of poor aromaticity. Copyright © 2013 John Wiley & Sons, Ltd.     

Real structure influence on the electron–phonon coupling properties of niobium

We performed density functional theory calculations using niobium (Nb) as a model system of a conventional superconductor, to correlate the distortion of twin defects with the electron–phonon coupling properties. Calculations using different settings of the Nb elementary cell (relaxed, distorted, super cell with zig‐zag twin defect) showed that only by including real structure elements into the setting, the Eliashberg spectral function representing the electron–phonon coupling properties was derived convincingly. Based on these density functional theory calculations of the electron–phonon cou‐ pling properties of Nb, we suggest a model for a combined superconducting/charge density wave ground state which uses a lattice distortion induced into the crystal by two‐dimensional defects as modulated background potential of the charge density wave phase. The coexistence of both phases is hereby necessary for a fine‐tuning of the Fermi surface within the small local domain of the defect to match the wavelength of the lattice distortion and the Fermi wavelength by pairing fermions to bosons. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Hartree–Fock and density functional theory study of remote substituent effects on heterolytic Fe―C bond energies of p‐G‐C6H4CH2Fe(CO)2(η5‐C5H5) and p‐G‐C6H4(H)(CN)CFe(CO)2(η5‐C5H5)

Knowledge of the strength of the metal–ligand bond breaking and formation is fundamental for an understanding of the thermodynamics underlying many important stoichiometric and catalytic organometallic reactions. Quantum chemical calculations at different levels of theory have been used to investigate heterolytic Fe―C bond energies of para‐substituted benzyldicarbonyl(η⁵‐cyclopentadienyl)iron, p‐G‐C₆H₄CH₂Fp [1, G = NO₂, CN, COMe, CO₂Me, CF₃, Br, Cl, F, H, Me, MeO, NMe₂; Fp = (η⁵‐C₅H₅)(CO)₂Fe], and para‐substituted α‐cyanobenzyldicarbonyl(η⁵‐cyclopentadienyl)iron, p‐G‐PANFp [2, PAN = C₆H₄CH(CN)]. The results show that BP86 and TPSSTPSS can provide the best price/performance ratio and more accurate predictions in the study of ΔH_het(Fe―C)'s. The good linear correlations [r = 0.98 (g, 1a), 0.99 (g, 2b)] between the substituent effects of heterolytic Fe―C bond energies [ΔΔH_het(Fe―C)'s] of series 1 and 2 and the differences of acidic dissociation constants (ΔpK_a) of C―H bonds of p‐G‐C₆H₄CH₃ and p‐G‐C₆H₄CH₂CN imply that the governing structural factors for these bond scissions are similar. And the excellent linear correlations [r = ?1.00 (g, 1c), ?0.99 (g, 2d)] between ΔΔH_het(Fe―C)'s and the substituent σ_p^? constants show that these correlations are in accordance with Hammett linear free energy relationships. The polar effects of these substituents and the basis set effects influence the accuracy of ΔH_het(Fe―C)'s. ΔΔH_het(Fe―C)'s(1, 2) follow the Capto‐dative Principle. The detailed knowledge of the factors that determine the Fp―C bond strengths would greatly aid in understanding reactivity patterns in many processes. Copyright © 2011 John Wiley & Sons, Ltd.     

Analysis of structure and vibrational spectra of 2,5‐dihydroxybenzoicacid based on density functional theory calculations

The spectra of 2,5‐dihydroxybenzoic acid (DHBA) have been recorded using Fourier transform‐infrared spectroscopy (FT‐IR) and FT‐Raman measurements. The total energy calculations of DHBA were evaluated for various possible conformers. The spectra were interpreted with the help of normal coordinate analysis based on density functional theory (DFT) using standard B3LYP/6–31G* method for the most optimized geometry. The effect of intramolecular hydrogen bonding was discussed. Normal coordinate calculations were performed with the DFT force field corrected by a recommended set of scaling factors, yielding fairly good agreement between observed and calculated frequencies. On the basis of the comparison between calculated and experimental results, assignments of fundamental modes were examined. Copyright © 2009 John Wiley & Sons, Ltd.     

Solid energy calibration standards for P K‐edge XANES: electronic structure analysis of PPh4Br

P K‐edge X‐ray absorption near‐edge structure (XANES) spectroscopy is a powerful method for analyzing the electronic structure of organic and inorganic phosphorus compounds. Like all XANES experiments, P K‐edge XANES requires well defined and readily accessible calibration standards for energy referencing so that spectra collected at different beamlines or under different conditions can be compared. This is especially true for ligand K‐edge X‐ray absorption spectroscopy, which has well established energy calibration standards for Cl (Cs₂CuCl₄) and S (Na₂S₂O₃·5H₂O), but not neighboring P. This paper presents a review of common P K‐edge XANES energy calibration standards and analysis of PPh₄Br as a potential alternative. The P K‐edge XANES region of commercially available PPh₄Br revealed a single, highly resolved pre‐edge feature with a maximum at 2146.96 eV. PPh₄Br also showed no evidence of photodecomposition when repeatedly scanned over the course of several days. In contrast, we found that PPh₃ rapidly decomposes under identical conditions. Density functional theory calculations performed on PPh₃ and PPh₄⁺ revealed large differences in the molecular orbital energies that were ascribed to differences in the phosphorus oxidation state (III versus V) and molecular charge (neutral versus +1). Time‐dependent density functional theory calculations corroborated the experimental data and allowed the spectral features to be assigned. The first pre‐edge feature in the P K‐edge XANES spectrum of PPh₄Br was assigned to P 1s → P‐C π* transitions, whereas those at higher energy were P 1s → P‐C σ*. Overall, the analysis suggests that PPh₄Br is an excellent alternative to other solid energy calibration standards commonly used in P K‐edge XANES experiments.     

Effect of thiophene rings on UV/visible spectra and non‐linear optical (NLO) properties of triphenylamine based dyes: a quantum chemical perspective

In this study, density functional theory (DFT) and time‐dependent DFT (TD‐DFT) theory are use to shed light on how the number of thiophene rings in π‐conjugated system influence the absorption spectra and non‐linear optical (NLO) properties of dyes. The results of theoretical computation show that the absorption spectra are gradually broadened and red‐shifted (384–542 nm) with increasing number of thiophene units. The theoretical examination on non‐linear optical properties was performed on the key parameters of polarizabilty and hyperpolarizability. A remarkable increase in non‐linear optical response was observed on insertion of thiophene rings in π‐spacer. Copyright © 2015 John Wiley & Sons, Ltd.