Quantum chemical studies on molecular conformations,energetic and intramolecular hydrogen bonding in ground and electronic excited state of (thioxosilyl) ethyleneselenol

In this work, a conformational analysis of (thioxosilyl) ethyleneselenol was performed using several computational methods, including density-functional theory (DFT) (B3LYP), MP2 and G2MP2. Harmonic vibrational frequencies were estimated at the same levels to confirm the nature of the stationary points found and also to account for the zero point vibrational energy correction. MES-1 and TES-1 conformers exhibit hydrogen bonding. This feature, although is not the dominant factor in the stability of conformers, appears to be of foremost importance to define the geometry of the molecule. Two intramolecular hydrogen bonds established between the polar groups were identified by the structural geometric parameters. These involved the thiol and selenol functional groups and were identified and characterized by the frequency shift in their stretching vibration modes. Furthermore, the excited-state properties of intramolecular hydrogen bonding have been investigated theoretically using the time-dependent DFT method. The influence of the solvent on the stability order of conformers and the strength of intramolecular hydrogen bonding was considered using the PCM (polarizable continuum model), SCI-PCM (self consistent isodensity-polarizable continuum model) and IEF-PCM (integral equation formalism-polarizable continuum model) methods. The “atoms in molecules” theory of Bader was used to analyze critical points and to study the nature of hydrogen bond in these systems. Natural bond orbital (NBO) analysis was also performed for better understanding the nature of intramolecular interactions. The calculated highest occupiedmolecular orbital and lowest unoccupied molecular orbital energies show that charge transfer occur within the molecule. Further verification of the obtained transition state structures was implemented via intrinsic reaction coordinate analysis. Calculations of the ¹H NMR chemical shift at the GIAO/B3LYP/6–311++G** level of theory are also presented.     

A computational investigation on the molecular structure,electronic properties and intramolecular hydrogen bonding interaction of 1,1,1-trifluoro-4-mercaptobut-3-ene-2-thione in ground and electronic excited state

The hydrogen bond (HB) strength, geometry optimization, vibrational frequencies and several well-established indices of aromaticity in 1,1,1-trifluoro-4-mercaptobut-3-ene-2-thione and its 15 derivatives in two positions, R1 and R2, have been investigated by means of the density functional theory (DFT) method with 6-311++G** basis set in the gas phase. The obtained results show that the HB strength is mainly governed by resonance variations inside the chelate ring induced by the substituent groups. The following substituents have been taken into consideration: NO₂, SCF₃, Ph, PhOCH₃, SCOCH₃, CH₂OCH₃ and CH₂OH. The strongest S–H···S HBs belong to PhOCH₃-substituted system in both positions, whereas NO₂ and H substitutions in R1 and R2 positions, respectively, produce the weakest S–H···S hydrogen bridges. The excited-state properties of intramolecular hydrogen bonding in substituted systems have been investigated theoretically using the time-dependent DFT method. Natural bond orbital analysis is also performed for a better understanding of the nature of intramolecular interactions. The electron density and Laplacian (?²ρ) properties, estimated by atoms in molecule calculations, indicate that the H···S bond possesses low ρ, positive ?² ρ and H_C<0, which are in agreement with the partially covalent character of HBs.     

Synthesis,X-ray Structure,Spectroscopic Properties and DFT Studies of a Novel Schiff Base

A series of Schiff bases, salicylideneaniline derivatives 1–4, was synthesized under mild conditions and characterized by ¹H NMR, HRMS, UV-Vis and fluorescence spectra, and single-crystal X-ray diffraction. In solid and aprotic solvents 1–4 exist mainly as E conformers that possess an intramolecular six-membered-ring hydrogen bond. A weak intramolecular C–H···F hydrogen bond is also observed in fluoro-functionalized Schiff base 4, which generates another S(6) ring motif. The C–H···F hydrogen bond further stabilizes its structure and leads it to form a planar configuration. Compounds 1–3 exhibit solely a long-wavelength proton-transfer tautomer emission, while dipole-functionalized Schiff base 4 shows remarkable dual emission originated from the excited-state intramolecular charge transfer (ESICT) and excited-state intramolecular proton transfer (ESIPT) states. Furthermore, the geometric structures, frontier molecular orbitals (MOs) and the potential energy curves for 1–4 in the ground and the first singlet excited state were fully rationalized by density functional theory (DFT) and time-dependent DFT calculations.     

Structure and Bonding in 2‐Diazo‐4,6‐Dinitrophenol (DDNP)

The structure and bonding in 2‐diazo‐4,6‐dinitrophenol (DDNP) is discussed on the basis of quantitative molecular orbital (MO) calculations at the density functional theory (DFT) level using the natural bond orbital analysis (NBO). Qualitative valence bond theory (VB) was used to generate an increased VB structure for DDNP. The increased‐valence structure is better in accordance with the computed and observed (X‐ray) geometry than is the NBO analysis.     

Electronic structure and spectral properties of the triarylamine-dithienosilole dyes for efficient organic solar cells

The recently synthesized high-performance triarylamine dyes with the dithienosilole π-conjugated spacer for efficient organic solar cells are calculated at the density functional theory (DFT) level with the Bader approach for the quantum theory of atoms in molecule (QTAIM) analysis. The presence of stabilizing intramolecular hydrogen bonds and Van der Waals interactions in the dye molecules is predicted and the energies of these interactions are estimated. The electronic bands nature in absorption spectra of the dyes is determined by the time-dependent DFT calculations with a linear response methodology using B3LYP and BMK hybrid functionals. Relations between incident light absorption intensity in the first long-wavelength band of the dye, its polarization, HOMO-LUMO orbital nature and the driving force of electron injection to the semiconductor are discussed.     

Electronic structures and photophysical properties of carbazole- and thiophene-based organic compounds used as hole-injecting layer for organic light-emitting diodes (OLEDs)

In this study, we have carried out a theoretical study on six organic compounds based on thiophene and carbazole, with the aim of using them as a hole-injecting layer of organic light-emitting diodes (OLEDs). In this study, we have tested two types of structures: D-π-D for MO1, MO2, MO3, and MO4 compounds and D-π-A for MO5 and MO6 compounds. The correlation structure-properties of these studied compounds have been proceeded and discussed by analyzing highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), energy gap, polarization effect, atom transition density matrix, absorption, and photoluminescence (PL). This theoretical study, based on density functional theory (DFT)/TPSSTPSS/aug-cc-pVQZ and the integral-equation-formalism polarizable continuum model/Coulomb attenuated method-Becke, 3-parameter, Lee–Yang–Parr (IEFPCM/TD-CAM-B3LYP)/6-31++G(d,p) is consolidated by experimental data for MO1, MO2, and MO4 compounds, allowing the determination of their structural and optoelectronic properties (HOMO, LUMO, gap [Eg], absorption, and emission parameters). The obtained results appear very conclusive and show that the performance of these compounds in terms of luminescence, absorption, and current–voltage (I–V) characteristics of OLED devices make them a promising candidate for the realization of light-emitting diodes.     

Hydrogen storage in ammonia triborane: Properties and behavior of the chemical bonds

We show in this paper by using quantum chemical methods how added hydrogen to cyclic triborane forms a 3c–2e bond to two boron atoms. Attached ammonia renders the storaged hydrogen more easily detached. The optimization of the structures were carried out at the MP2/6-311++G⁷ level of theory and the bonding properties were then analyzed by topological methods applied to charge density as well as by the methods based upon natural bonding orbital theory.     

Experimental and theoretical insight into the electronic properties of 4-aryl-5-arylazo-3-cyano-6-hydroxy-2-pyridone dyes

In this paper, spectroscopic and quantum mechanical investigation of nine 4-aryl-5-arylazo-3-cyano-6-hydroxy-2-pyridone dyes was performed, and obtained density functional theory (DFT) results were compared with experimental data. The structural and spectroscopic properties of azo-2-pyridone dyes were studied by DFT using B3LYP, CAM-B3LYP, and M06-2X methods with a 6-311++G(d,p) basis set. Comparison of results reveals that the scaled theoretical vibrational frequencies of azo dyes are in good agreement with experimental data. The time-dependent DFT calculated and experimental ultraviolet-visible (UV-vis) absorption spectra are also in good agreement. The effect of electron-donating –OCH₃ and electron-withdrawing –NO₂ groups on the structural parameters, vibrational frequencies, UV-vis absorption, and natural bond orbital (NBO) atomic charges were thoroughly analysed. Vibrational, UV-vis, and NBO analyses confirm that investigated dyes exist in the hydrazo tautomeric form in the solid state and ethanol solution. These analyses signify the occurrence of intramolecular charge transfer in these azo-pyridone dyes.     

The structure of hydrated complexes of o-hydroxybenzoic acid in water-modified supercritical carbon dioxide: The Car-Parrinello molecular dynamics simulation

The study of the o-hydroxybenzoic acid (o-HBA)–water molecular structures formed in supercritical carbon dioxide (T = 318 K, ρ = 0.7 g/cm³) by Car-Parrinello molecular dynamics method has been performed. Atom–atom radial distribution functions, coordination numbers, average hydrogen bond (HB) numbers, and vibrational densities of states have been calculated from molecular trajectories saved during simulation procedure. It has been shown that, despite of the high co-solvent polarity, the hydroxyl group of the o-HBA preferably forms an intramolecular HB, whereas o-HBA–water hydrogen bonding involves only acid carboxyl group. The formed o-HBA–(H₂O)₂ complex and remaining water molecules compose a labile hydrogen-bonded cluster. The average HB number per water molecule is equal to 1.93, 26.4% out of the total amount of HBs formed by water molecules being water–o-HBA HBs, and the rest being water–water HBs. Evolution of hydrogen-bonded clusters has been analyzed, using instantaneous structures saved during the simulation. It was shown that water–water HBs are less stable than water–o-HBA ones.     

A DFT study of electronic structures, energies, and molecular properties of lithium bis[croconato]borate and its derivatives

Theoretical studies on electrolyte salts, lithium bis[croconato(2-)]borate (LBCB) and its derivatives, lithium [croconato(2-) salicylato(2-)]borate (LCSB), and bis[salicylato(2-)]borate (LBSB) are carried out using density functional theory (DFT) method and B3LYP theory level for the first time. Bidentate structures involving two oxygen atoms are preferred. Based on these conformations, a linear correlation was observed between the highest occupied molecular orbital (HOMO) energies and the limiting oxidation potentials measured by linear sweep voltammetry, which supports experimental results that strongly electron-withdrawing substituent anions are more resistant against oxidation than their organic counterparts. The correlations were also observed between ionic conductivity and binding energy, solubility and theoretical set of parameters of anion_, thermal stability and the hardness (η)_. Wave function analyses have been performed by natural bond orbital (NBO) method to further investigate the cation-anion interactions.     

功能化离子液体1-(3-磺酸)丙基-3-甲基咪唑硫酸氢盐[HSO3-(CH2)3-mim][HSO4]的微观结构及阴阳离子之间的相互作用

采用密度泛函理论(DFT)的B3PW91/6-311+ G(d)方法,对Br(o)nsted酸功能化离子液体1-(3-磺酸)丙基-3-甲基咪唑硫酸氢盐[HSO3-(CH2)3-mim][HSO4]进行了结构优化、频率分析和自然键轨道(NBO)分析.离子对的微观结构及其原子电荷分布和电荷转移情况表明阴阳离子之间存在较强的...     

The Role of Adsorbate–Adsorbate Interactions in the Rate Controlling Step and the Most Abundant Reaction Intermediate of NH3 Decomposition on Ru

N–N adsorbate–adsorbate interactions on a Ru(0001) surface are first estimated using quantum mechanical density functional theory (DFT) calculations, and subsequently incorporated, for the first time, in a detailed microkinetic model for NH₃ decomposition on Ru using the unity bond index-quadratic exponential potential (UBI–QEP) method. DFT simulations indicate that the cross N–H interactions are relatively small. Microkinetic model predictions are compared to ultra-high vacuum temperature programmed desorption and atmospheric fixed bed reactor data. The microkinetic model with N–N interactions captures the experimental features quantitatively. It is shown that the N–N interactions significantly alter the rate determining step, the most abundant reaction intermediate, and the maximum N*-coverage, compared to mechanisms that ignore adsorbate–adsorbate interactions.     

Experimental and DFT calculated structure of the diruthenium(2.5) complex [(Me3TACN)Ru(μ-Cl)3Ru(Me3TACN)](PF6)2

The diruthenium(2.5) complex [(Me₃TACN)Ru(μ-Cl)₃Ru(Me₃TACN)]-(PF₆)₂, Me₃TACN = 1,4,7-trimethyl-1,4,7-triazacyclononane, has been crystallized for structural characterization. The results are reproduced by density functional theory (DFT) calculations and confirm the sensitivity of the central Ru(μ-Cl)₃Ru core to contacts between the Cl bridging atoms and the co-ligands. The singly occupied MO is characterized as a σ* MO involving the metal d_z² orbitals and a small halide contribution by DFT calculations and EPR.     

Investigation of aggregation induced emission in 4-hydroxy-3-methoxybenzaldehyde azine and polyazine towards application in (opto) electronics: synthesis,characterization, photophysical and electrical properties

An azine monomer 4-hydroxy-3-methoxybenzaldehyde azine was synthesized by refluxing with ethanolic solution of vanillin with hydrazine hydrate. It was then converted into polyazine by oxidative polymerization. The structure of azine and polyazine was characterized by FT-IR, UV–visible, ¹H-NMR and ¹³C-NMR. Spectral results suggest the formation of polymer, through C–C and C–O–C coupling of the phenylene and oxyphenylene. The relationship between the structures and photophysical properties of azine and polyazine was studied. Both azine and polyazine show, aggregation induced emission with increase in concentration in DMSO solution. The single crystal structure of azine suggesting the various inter and intra molecular interactions rigidify the conformation and locked the intramolecular rotations of the phenyl rings in the molecule. The inhibition of intramolecular rotation, J- aggregation and increase of conjugation impart the fluorescence in aggregated state. Additionally, the electronic properties namely orbital energies and resulting energy gap calculated theoretically by density functional theory (DFT).     

Synthesis,Structural, and Theoretical Studies of Quinazoline-2,4-dione Derivatives

New quinazolin-2,4-dione derivatives have been synthesized and fully characterized. The new derivatives were synthesized using 3-(2-imino-4-oxo-3H,4H,5H-thiazolidin-3-yl)-1H-quinazolin-2,4-dione by nucleophilic addition mechanism. DFT calculations using B3LYP/6–311++G(d,p) level of the theory were used to investigate the molecular structures and the relative stabilities of the anticipated isomers (E and Z). Both experimental and theoretical calculations confirmed the higher stability of the Z-isomers compared to the E-isomers. The former is stabilized by two intramolecular hydrogen bonds compared to only one in the latter isomer. The frontier orbital calculations (HOMO and LUMO), and the energy gap confirmed the stability of the molecules.     

用密度泛函理论研究LAX-112与氟化氢分子间的相互作用

在DFT-B3LYP/6-311++G**水平上,计算获得3,6-二氨基-1,2,4,5-四嗪-1,4-二氧化物(LAX-112)与氟化氢(HF)超分子体系势能面上3种全优化几何构型。经基组叠加误差(BSSE)和零点能(ZPE)校正,求得LAX-112与HF分子间的最大相互作用能为-34.41kJ/mol。超分子体系中的电子均由LAX-112向HF转移。用自然键轨道(NBO)分析揭示了分子间的相互作用主要由强氢键所贡献。对优化构型进行了振动频率计算,结果表明,超分子体系中H-X(X=N和F)的伸缩振动频率均发生了大幅度红移。基于统计热力学求得200.0～800.0K温度范围从单体形成二聚体的热力学性质变化,发现二聚过程在较低温度或常温下均能自发进行。     

含能材料分子N8H8结构与性质的理论研究

采用密度泛函理论的b3lyp方法在6-311＋＋G＊＊基组上对30种N8H8链状异构体进行了理论计算,并应用分子中的原子理论（Atoms In Molecules,AIM）和自然键轨道理论（Nature Bond Orbital,NBO）分析了这些化合物相对稳定性和成键特征,G3MP2方法计算了各异构体的能量及生成热。结果表明：N8H8链状异构体中,含有N=N双键特征的异构体稳定性较好,影响氮氮键键长变化的主要因素是N原子孤对电子到相邻的氮氮键的超共轭作用;所有异构体中α3的生成热最大,β15的密度最大。     

An ab initio study on properties of cationic chalcogen bonds in XF2Y+⋯NCZ (X═H,CN, F; Y═S,Se; Z═H,Cl, Br) complexes

The geometries, interaction energies, and bonding properties of cationic chalcogen bonds are studied in binary complexes XF₂Y⁺?NCZ (X═H, CN, F; Y═S, Se; Z═H, Cl, Br). The nature of these interactions is studied by a vast number of methods, including molecular electrostatic potential (MEP), Noncovalent Interaction Index (NCI), quantum theory of atoms in molecules (QTAIM), and natural bond orbital (NBO) analyses. The interaction energies of these complexes vary between ?20.94?kcal/mol in HF₂S⁺?NCH and ?33.72?kcal/mol in F₃Se⁺?NCBr. According to the QTAIM analysis, all these cationic chalcogen bonds are classified as a closed-shell interaction with a partial covalent character. Moreover, cooperative effects between cationic chalcogen bond and hydrogen or halogen bond interactions are studied in ternary XF₂Y⁺?NCZ?NH₃ complexes. These cooperative effects are analyzed in terms of the parameters derived from the QTAIM and NBO analyses, and electron density difference plots.     

Consequences of Protonation of Diamines in the Gas Phase and the Solid State

An interesting model class of compounds are proton sponges—aromatic diamines characterized by exceptional basicity, such as 1,8-bis(dimethylamino)naphthalene (DMAN). For these compounds, protonation causes substantial redistribution of electron density which may be traced by observing the changes of structural parameters as well as of the properties of electron density at bond critical points. On protonation, electron density in DMAN goes from the terminal atoms towards the center of the molecule. This redistribution can also be confirmed by good quality neutron structural data. An ionic complex of DMAN with triformylmethane (TFM) acid has been studied by X-ray diffraction. We propose a multicenter model of hydrogen bonding {[Me₂N–H^0.5….^0.5H–NMe₂]⁺… X⁻} in this complex. The influence of weak intermolecular interactions of the DMANH⁺ cation with the nearest electronegative atom from the counterion on the strong intramolecular [N–H···N]⁺ hydrogen bonding has been demonstrated. Such interactions affect the localization of the proton in the intramolecular [N–H···N]⁺ hydrogen bridge.     

A Theoretical Study on the Influence of Carbon and Silicon Doping on the Structural and Electronic Properties of (BeO)12 Nanocluster

The influence of carbon and silicon atoms doping on the structural and electronic properties of the (BeO)₁₂ nanocluster is investigated through density functional theory calculations. It has been found that doping process induces local deformation at bond lengths and angles near the doping site. The results indicate that C or Si doping decreases the energy gap of the (BeO)₁₂ nanocluster. It seems that the electronic character of the (BeO)₁₂ nanocluster could be adjusted by particular impurity. The electronic charge distributions are also analyzed using Atoms in Molecules theory. Natural bond orbital analyses are also performed for scrutinizing the structural properties of the considered nanoclusters.