Experimental, theoretical calculations of the vibrational spectra and conformational analysis of 2,4-di-tert-butylphenol

In the present work, we reported a combined experimental and theoretical study on conformational stability, molecular structure and vibrational spectra of 2,4-di-tert-butylphenol (2,4-DTBP). The FT-IR (400-4000cm(-1)) and FT-Raman spectra (50-3500cm(-1)) of 2,4-DTBP were recorded. The molecular geometry, harmonic vibrational frequencies and bonding features of 2,4-DTBP in the ground-state have been calculated by using the density functional BLYP/B3LYP methods. The energy calculated by time-dependent density functional theory (TD-DFT) result complements with the experimental findings. The calculated highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energies show that charge transfer occurs within the molecule. Finally the calculation results were compared with measured infrared and Raman spectra of the title compound which showed good agreement with observed spectra.     

Spectroscopic, electronic structure and natural bond orbital analysis of o-fluoronitrobenzene and p-fluoronitrobenzene: a comparative study

Experimental FTIR, FT-Raman and FT-NMR spectroscopic studies of o-fluoronitrobenzene and p-fluoronitrobenzene have been carried out. A detailed quantum chemical calculations have been performed using DFT/B3LYP method with 6-311++G** and 6-31G** basis sets. Complete vibrational analyses of the compounds were performed. The temperature dependence of thermodynamic properties has been analysed. The atomic charges, electronic exchange interaction and charge delocalisation of the molecule have been performed by natural bond orbital (NBO) analysis. Molecular electrostatic surface potential (MESP), total electron density distribution and frontier molecular orbitals (FMOs) are constructed at B3LYP/6-311++G** level to understand the electronic properties. The charge density distribution and site of chemical reactivity of the molecules have been obtained by mapping electron density isosurface with electrostatic potential surfaces (ESP). The electronic properties, HOMO and LUMO energies were measured by time-dependent TD-DFT approach. (1)H and (13)C NMR spectra were recorded and (1)H and (13)C nuclear magnetic resonance chemical shifts of the molecule were calculated. The (1)H and (13)C nuclear magnetic resonance (NMR) chemical shifts of the molecules in chloroform solvent and in gas phase were calculated by using the Gauge-Independent Atomic Orbital (GIAO) method and are found to be in good agreement with experimental values. The theoretical parameters obtained at B3LYP levels have been compared with the experimental values.     

Molecular structure, vibrational spectroscopic (FT-IR, FT-Raman), UV and NBO analysis of 2-chlorobenzonitrile by density functional method

In this work, we will report a combined experimental and theoretical study on molecular structure, vibrational spectra, NBO and UV spectral analysis of 2-chlorobenzonitrile (2-ClBN). The FT-IR solid phase (4000-400 cm(-1)), and FT-Raman spectra (3500-50 cm(-1)) of 2-ClBN was recorded. The molecular geometry, harmonic vibrational frequencies and bonding features of 2-ClBN in the ground state have been calculated by using the density functional methods (BLYP, B3LYP) with 6-31G(d,p) as basis set. The assignments of the vibrational spectra have been carried out with the help of normal co-ordinate analysis (NCA) following the Scaled Quantum Mechanical Force Field Methodology (SQMFF). Stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The results show that charge in electron density (ED) in the σ* and π* anti bonding orbitals and E2 energies confirms the occurrence of ICT (Intra molecular Charge Transfer) within the molecule. The UV spectrum was measured in ethanol solution. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) results complements with the experimental findings. The calculated HOMO and LUMO energies also confirm that charge transfer occurs within the molecule. Finally calculated results were applied to simulated Infrared and Raman spectra of the title compound which show good agreement with observed spectra.     

Synthesis,molecular conformation,vibrational, electronic transition,and chemical shift assignments of 4-(thiophene-3-ylmethoxy)phthalonitrile: a combined experimental and theoretical analysis

This work presents the synthesis and characterization of a novel compound, 4-(thiophene-3-ylmethoxy)phthalonitrile (TMP). The spectroscopic properties of the compound were examined by FT-IR, FT-Raman, NMR, and UV techniques. FT-IR and FT-Raman spectra in solid state were observed in the region 4000–400 cm⁻¹ and 3500–50 cm⁻¹, respectively. The ¹H and ¹³C NMR spectra were recorded in CDCl₃ solution. The UV absorption spectrum of the compound that dissolved in THF was recorded in the range of 200–800 nm. The structural and spectroscopic data of the molecule in the ground state were calculated using density functional theory (DFT) employing B3LYP exchange correlation and the 6-311++G(d,p) basis set. The vibrational wavenumbers were calculated and scaled values were compared with experimental FT-IR and FT-Raman spectra. The complete assignments were performed on the basis of the experimental results and total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. Isotropic chemical shifts (¹³C NMR and ¹H NMR) were calculated using the gauge-invariant atomic orbital (GIAO) method. A study on the electronic properties, such as HOMO and LUMO energies, were performed by time-dependent DFT (TD-DFT) approach. The HOMO and LUMO analyses have been used to elucidate information regarding charge transfer within the molecule. Comparison of the calculated frequencies, NMR chemical shifts, absorption wavelengths with the experimental values revealed that DFT method produces good results.     

DFT study of the physicochemical characteristics and spectral behavior of new 8‐substituted 1,3,7‐trimethylxanthines

Nine biologically active theophylline derivatives were investigated using quantum chemical methods (density functional theory level). All calculations were performed at B3LYP/6‐31G** level of theory. The electrostatic potential charges, highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) gap, dipole moment, vibration frequencies, and electronic spectra were calculated. Log P was determined by Ghose‐Crippen method. All of the compounds under study are polar and negatively charged, which is necessary for their interaction with the receptors/enzymes. Majority of the compounds are lipophilic and they can easily diffuse through the cell membrane. The observed differences between the calculated and the experimental vibration frequencies in the Fourier Transform Infrared Spectroscopy (FTIR) spectra are established to be mainly in NH and OH bands, due to hydrogen bonds formation. The discrepancies between theoretical and experimental electronic spectra may be due to vibration effects and H‐bonding with the solvent molecules. The obtained results show that this type of spectrum is formed mainly by the xanthine fragment of the molecule, especially in the fingerprint region. All calculated properties could be useful for future qualitative‐structure activity relationship (QSAR) analysis. © 2012 Wiley Periodicals, Inc.     

Theoretical Studies on the Electronic Structures and Spectral Properties of 4,4′-（Ethane-1,2-diylbis-（oxy））dibenzaldehyde and Its Polymorph

The ground state geometries, frontier molecular orbital properties, and absorption properties of 4,4′-(ethane-1,2-diylbis(oxy))dibenzaldehyde (EDO-DBDHD) and its polymorph have been studied theoretically. The density functional theory (DFT) method was employed to optimize the ground state geometries, and theoretical data reveal that EDO-DBDHD features the planar molecular conformations, in contrast to V-shaped structures of its polymorph, which agrees with the experimental data. Additionally, the absorption spectra of both compounds were predicted using time-dependent density functional theory (TDDFT). The calculated results show that the lowest lying absorption bands of these compounds have the transition configurations of HOMO → LUMO, resulting in the transition character of π→π*/n→π*. The transition of HOMO → LUMO+3 mainly contributes to the highest lying absorption bands of two compounds at 225 nm with the character of π→π*/n→π*.     

Molecular structure,vibrational spectra,NBO analysis,first hyperpolarizability,and HOMO,LUMO studies of mesityl chloride by density functional methods

The FT-IR and FT-Raman vibrational spectra of mesityl chloride (2,4,6-trimethylbenzyl chloride) were recorded. The optimized geometry and wavenumbers in the ground state were calculated using density functional (B3LYP, and B3PW91) methods with standard 6-311G(d,p) basis set. The computed B3PW91/6-311G(d,p) results show the best agreement with the experimental values over the other methods. Natural bond orbital analysis of mesityl chloride is also carried out, which confirms the occurrence of strong intermolecular bonding, stability of the molecule arising from hyperconjugative interactions, and charge delocalization. The electric dipole moment (μ), polarizability (α), and first hyperpolarizability (β₀) which results also show that the mesityl chloride might have microscopic non-linear optical behavior with non-zero values. The calculated HOMO and LUMO energies show that charge transfer occur in the molecule. The results of the calculations were applied to simulated spectra of the title compound, which show excellent agreement with observed spectra.     

Molecular structure, vibrational spectroscopic, first-order hyperpolarizability and HOMO, LUMO studies of 2-aminobenzimidazole

In the present work, we reported a combined experimental and theoretical study on molecular structure, vibrational spectra and HOMO-LUMO analysis of 2-aminobenzimidazole (2-ABD). The FTIR (400-4000 cm(-1)) and FT-Raman spectra (50-3500 cm(-1)) of 2-ABD were recorded. The molecular geometry, harmonic vibrational wavenumbers and bonding features of 2-ABD in the ground-state have been calculated by using the density functional B3LYP method with 6-311++G(d,p) and 6-31G(d) as basis sets. The energy and oscillator strength were calculated by time-dependent density functional theory (TD-DFT) result complements with the experimental findings. The calculated HOMO and LUMO energies showed that charge transfer occurs within the molecule. Finally, the calculation results were applied to simulate infrared and Raman spectra of the title compound which showed good agreement with the observed spectra.     

Synthesis and Electrochemical and Photophysical Properties of Azaterrylene Derivatives

A series of terrylene derivatives, such as monoazaterrylene (MATerry), 1,6‐diazaterrylene (DiATerry) and pristine terrylene (Terry), were synthesized by changing the number of nitrogen atoms at the bay region (1 and 6 positions of the Terry core). The electrochemical measurements suggested that the first one‐electron reduction and oxidation potentials became positively shifted with increasing numbers of nitrogen atoms. This agreed with the energies of the corresponding highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) states estimated by DFT methods. In contrast, the HOMO–LUMO gaps approximately remained constant. This trend is quite similar to the spectroscopic behaviors observed by absorption and fluorescence spectra. The solvent polarity‐dependent spectroscopic trends of DiATerry suggested the intramolecular charge‐transfer (ICT) characters. The evaluation of the excited‐state dynamics in various solvents indicated the electronic configurational changes of the excited states relative to the ground state via the ICT. This was supported by the Lippert–Mataga plots. Finally, the reversible protonation and deprotonation processes were also observed.     

抗癌性吲哚喹唑啉衍生物的定量构效关系

用量子化学密度泛函理论(DFT)、分子力学(MM＋)及回归分析方法,对一系列抗癌性吲哚喹唑啉衍生物进行了定量构效关系(QSAR)的研究.通过回归分析,筛选了影响抗癌活性的主要因素,建立了定量构效关系方程.结果表明,化合物的最低未占据分子轨道(LUMO)与最高占据分子轨道(HOMO)之间的能量差(ΔεL-H)、分子的疏水性(lgP)以及环D上的总电荷(ΣQD)和环D上R1取代基的第一个原子的净电荷(QFR1)是影响化合物抗癌活性的主要因素.所得模型对化合物抗癌活性有较好的预测效果. 同时, 与ΔεL-H密切相关的LUMO轨道能量及共轭平面面积对药物的DNA-结合及其活性起着十分重要的作用,可通过选取具有较强的拉电子性质同时又能与本系列化合物的骨架形成更大共轭体系的取代基R1,设计抗癌活性较高的化合物.     

Fine-tuning the molecular energy levels by incorporating thiophene units onto the π-backbone of core-expanded naphthalene diimides

A series of core-expanded naphthalene diimides (NDI-DTYM) and thiophene-based derivatives (1a-c) were designed and synthesized to investigate the relationship between molecular structures and the highest occupied molecular orbital (HOMO) energy levels but has little impact on the lowest unoccupied molecular orbital (LUMO) energy levels. The results demonstrated that increasing the number of thiophene units can gradually elevate the HOMO energy levels but had little impact on the LUMO energy levels. The n-channel organic field-effect transistors (OFETs) based on 1b and 1c have demonstrated that these almost unchanged LUMO energy levels are proper to transport electrons.     

Synthesis,characterization of novel quinoline-2-carboxamide based chalcone derivatives and their molecular docking,photochemical studies

Abstract

Novel series of quinoline-2-carboxamide based chalcone derivatives (5a–g) have synthesized and characterized using ¹H-NMR, 13C-NMR, Mass, and elemental analysis. In-silico molecular docking studies exhibited that synthesized compounds 5a and 5g are good binding energy (?8.46?kcal and ?9.46?kcal) toward the essential requirements of targeted compounds for EGFR receptor-bearing quinazoline inhibitor (PDB ID: 1M17(Lapitinib)). UV-Vis and fluorescence spectroscopy measurements provided a significant effect on the absorption, emission cyclic voltammetry (CV), and highest occupied molecular orbital (HOMO). Lowest unoccupied molecular orbital (LUMO) values of compound 5g are also confirmed band along with intramolecular charge transfer character (D-π-A). The red shift maxima (510?nm) the emission spectra in various solvents with increasing solvent polarity.     

Vibrational spectroscopy (FT-IR and FT-Raman) investigation, and hybrid computational (HF and DFT) analysis on the structure of 2,3-naphthalenediol

The FT-IR and FT-Raman vibrational spectra of 2,3-naphthalenediol (C(10)H(8)O(2)) have been recorded using Bruker IFS 66V spectrometer in the range of 4000-100 cm(-1) in solid phase. A detailed vibrational spectral analysis has been carried out and the assignments of the observed fundamental bands have been proposed on the basis of peak positions and relative intensities. The optimized molecular geometry and vibrational frequencies in the ground state are calculated by using the ab initio Hartree-Fock (HF) and DFT (LSDA and B3LYP) methods with 6-31+G(d,p) and 6-311+G(d,p) basis sets. There are three conformers, C1, C2 and C3 for this molecule. The computational results diagnose the most stable conformer of title molecule as the C1 form. The isotropic computational analysis showed good agreement with the experimental observations. Comparison of the fundamental vibrational frequencies with calculated results by HF and DFT methods. Comparison of the simulated spectra provides important information about the capability of computational method to describe the vibrational modes. A study on the electronic properties, such as absorption wavelengths, excitation energy, dipole moment and Frontier molecular orbital energies, are performed by time dependent DFT approach. The electronic structure and the assignment of the absorption bands in the electronic spectra of steady compounds are discussed. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. On the basis of the thermodynamic properties of the title compound at different temperatures have been calculated. The statistical thermodynamic properties (standard heat capacities, standard entropies, and standard enthalpy changes) and their correlations with temperature have been obtained from the theoretical vibrations.     

Synthesis,Characterization, and Computational Studies of Selenium Derivatives of 3,5‐Dichloropyridine

A methodology that can be tailored to incorporate selenium at the C‐2 or C‐4 position of 3,5‐dichloropyridine ( 1 ) was developed. For this, the lithiation of 1 with and without prior boron trifluoride complexation was utilized. The use of 1.3 equiv of LDA in the reaction did not give the desired product; however, the use of 2.3 equiv of LDA successfully inserted selenium into the C─Li bond. The observed regioselectivity in these reactions has been explained in light of relative stability of the lithiated species formed in dimethyl ether solution. Quantum chemical analysis was used to calculate the deprotonation energy and pK _a values and correlated with the observed regioselectivity. Theoretical analysis (B3LYP/6‐311++G(d,p)) of the synthesized compounds was performed to predict the effect of structural variations on the molecular properties of pyridylselenium derivatives. Various thermodynamic parameters and HOMO‐LUMO energies in the gas and solvent phases were calculated. When compared with 1 , the insertion of selenium into a pyridine moiety drastically reduces the HOMO‐LUMO energy gap, which clearly explains photochemical liability of selenium‐containing pyridine derivatives. The ¹H‐ and ¹³C‐NMR chemical shifts were also calculated by using gauge‐including atomic orbital method, and the results were validated with the experimental data.     

New materials based on thiazolothiazole and thiophene candidates for optoelectronic device applications: theoretical investigations

We report theoretical analysis on the geometries and electronic properties of new conjugated compounds based on thiazolothiazole synthesized by Ando et al. (Synth. Met., 156:327 [13]). The theoretical ground-state geometry and electronic structure of the studied molecules were investigated by the density functional theory (DFT) method at Becke’s three-parameter functional and Lee–Yang–Parr functional (B3LYP) level with 6-31G(d,p) basis set. The effects of the ring structure and the substituents on the geometries and electronic properties of these materials are discussed to investigate the relationship between molecular structure and optoelectronic properties. This investigation was used to drive further syntheses towards compounds more useful as active optoelectronic materials. Theoretical knowledge of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the components is basic in studying organic solar cells, so the HOMO, LUMO, and gap energy V _oc (open-circuit voltage) of the studied compounds are calculated and discussed. These properties suggest these materials as good candidates for use in organic dye-sensitized solar cells.     

Theoretical and experimental investigations of complexation with BF3.Et2O effects on electronic structures,energies and photophysical properties of Anil and tetraphenyl (hydroxyl) imidazol

The novel compounds (E)‐2‐(((4‐hydroxyphenyl)imino)methyl)phenol, Tetraphenyl (hydroxyl) imidazole and their corresponding Boron difluoride complexes were synthesized and characterized by spectroscopic techniques. Density functional theory calculations at B3LYP‐D3/6–311++G (d, p) level of theory were performed for the geometric parameters. The MEP surface studies were used to understand the behavior of molecules in terms of charge transfer and to determine how these molecules interact. We used the GIAO and the B3LYP‐D3 with a 6–311++ G (d, p) basis set to simulate the (¹H‐NMR and ¹⁹F‐NMR) and the IR spectra, respectively. The corresponding calculated results are in good agreement with the experimental data. The stability of the molecule arising from hyperconjugation interaction and charge delocalization were analyzed using NBO analysis. FMOs revealed the occurrence of charge transfer within the molecule. The complexation using BF₃.Et₂O was also found to have remarkable effects on the electrochemical properties of the studied molecules, where (b) and (d) present lower chemical stability, higher reactivity and higher polarizability than (a) and (c), respectively. Moreover, the energy gap of (a) and (c) decreased after complexation using BF₃.Et₂O, indicating the reliability of the electrochemical evaluation of LUMO and HOMO energy levels. These values are the factors explaining the possible charge transfer interaction within the molecule. The absorption and emission spectra of the model compound were also simulated and compared to experimental observations in the DMF solvent. The results of DFT calculations supported the structural and spectroscopic data and confirmed the structure modification of frontier molecular orbitals for BF₂ complexes as well as tunable potentials and energy levels.     

(Dibenzoylmethanato)boron Difluoride Derivatives Containing Triphenylamine Moieties: A New Type of Electron‐Donor/π‐Acceptor System for Dye‐Sensitized Solar Cells

(Dibenzoylmethanato)boron difluoride derivatives containing triphenylamine moieties were synthesized as a new type of electron‐donor/π‐acceptor system. These new compounds exhibited long‐wavelength absorptions in the UV/Vis spectra, and reversible oxidation and reduction waves in cyclic voltammetry experiments. Their amphoteric redox properties are based on their resonance hybrid forms, in which a positive charge is delocalized on the triphenylamine moieties and a negative charge is localized on the boron atoms. Molecular orbital (MO) calculations indicate that their HOMO and LUMO energies vary with the number of phenylene rings connected to the difluoroboron‐chelating ring. This is useful for optimizing the HOMO and LUMO levels to an iodine redox (I^?/I₃^?) potential and a titanium dioxide conduction band, respectively. Dye‐sensitized solar cells fabricated by using these compounds as dye sensitizers exhibited solar‐to‐electric power conversion efficiencies of 2.7–4.4 % under AM 1.5 solar light.     

Synthesis,Crystal Structure and Spectroscopic Properties of 1,2-Benzothiazine Derivatives:An Experimental and DFT Study

1,2-Benzothiazine derivatives methyl 3-methoxy-4-oxo-3,4-dihydro-2H-benzo[e] [1,2]thiazine-3-carboxylate 1,1-dioxide(1) and methyl 2-ethyl-3-hydroxy-4-oxo-3,4-dihydro-2Hbenzo[e][1,2]thiazine-3-carboxylate 1,1-dioxide(2) were synthesized, and characterized by spectroscopic techniques; 1H-NMR and infrared(IR) spectroscopy. Crystals of 1 and 2 were grown by slow evaporation of methanol and ethyl acetate, respectively and their crystal structures were investigated by single-crystal X-ray diffraction analysis. Geometric properties were calculated by the B3 LYP method of density functional theory(DFT) at the 6-31G+(d) basis set to compare with the experimental data. Simulated properties were found in strong agreement with the experimental ones. Intermolecular forces have also been modeled in order to investigate the strength of packing and strong hydrogen bonding was observed in both compounds 1 and 2. Electronic properties such as Ionization Potential(IP), Electron Affinities(EA) and coefficients of the highest occupied molecular orbital(HOMO) and the lowest unoccupied molecular orbital(LUMO) of com- pounds 1 and 2 were simulated for the first time.     

Modulation of molecular conductance induced by electrode atomic species and interface geometry

We present a systematic theoretical investigation of the interaction of an organic molecule with gold and palladium electrodes. We show that the chemical nature of the electrode elicits significant geometrical changes in the molecule. These changes, which are characteristic of the electrode atomic species and the interface geometry, are shown to occur at distances as great as 10 Angstrom from the interface, leading to a significant modification of the inherent electronic properties of the molecule. In certain interface geometries, the highest occupied molecular orbital (HOMO) of the palladium-contacted molecule exhibits enhanced charge delocalization at the center of the molecule, compared to gold. Also, the energy gap between the conductance peak of the lowest unoccupied molecular orbital (LUMO) and the Fermi level is smaller for the case of the palladium electrode, thereby giving rise to a higher current level at a given bias than the gold-contacted molecule. These results indicate that an optimal choice of the atomic species and contact geometry could lead to significantly enhanced conductance of molecular devices and could serve as a viable alternative to molecular derivatization.     

Theoretical Study on Electronic,Optical, and Charge Transfer Properties of Starburst Triphenylamine as Sensibilizer @TiO_2 Cluster for Dye-sensitized Solar Cells

Here, a series of starburst triphenylamine(WD8) derivatives for dye-sensitized solar cells(DSSCs) applications have been designed. The frontier molecular orbitals(FMOs) property, absorption spectra, and charge transfer rate property of WD8 and its derivatives were simulated. We also evaluated the FMOs energies and absorption spectra of WD8 and its derivatives with the TiO2 cluster. The simulation results show that the phenothiazine-triphenylamine and 2-cyanoacetic acid groups in the ortho-position will increase the HOMO energy, decrease the LUMO energy, and narrow the HOMO-LUMO gap of WD8. The charge injection from WD8 and its derivatives to TiO2 should be more favorable. The phenothiazine-triphenylamine and 2-cyanoacetic acid groups in the ortho-position will decrease the electron and hole injection barriers of WD8. The phenothiazinetriphenylamine and 2-cyanoacetic acid groups in the ortho-position will improve the absorption spectra properties of WD8. The absorption spectra of WD8 and its derivatives with the TiO2 cluster would have a red shift. The phenothiazine-triphenylamine and 2-cyanoacetic acid groups in the ortho-position will increase the charge transfer property of WD8.