Standard 6-31G Research Articles

Theoretical studies and temperature-dependent Raman spectroscopy of Schiff's bases 5O.12 liquid crystalline compound

Comparative Raman spectra and different physical properties of 5O.12 liquid crystal compound using density functional theory is studied in this article. The molecular structure of 5O.12 liquid crystal has been optimized by using density functional theory (DFT). The Raman spectroscopy examination is critical for observing the properties and behavior of liquid crystals. 5O.12 is a Schiff-based with several liquid crystalline phases, including Nematic, Smectic A, and Smectic B. The phases of the liquid crystal vary as the temperature changes, providing essential information about the liquid crystal's molecular arrangement. The density functional theory with standard basis set 6–31 G (d, p) paired with B3LYP functional is used to study the theoretical Raman spectra and various physical properties. Theoretical details of Raman spectra give excellent agreement with experimental results. Experimental Raman spectra were examined with temperature in all of the observed phases in this article. Comparative Raman studies at different temperatures help in understanding thermodynamic and structural behavior of molecular systems. Peak positions and line width are investigated further as temperature varies, yielding precise and significant information about the molecule's ordering and behaviour. DFT is used to do research on different physical properties like HOMO LUMO, relative energy gaps and various thermochemical properties such as entropy, heat capacity, thermal energy. These characteristics give an understanding of the stability of molecules, as well as the optical properties and structure of liquid crystalline compounds.

Band Gap Energy of Periodic Anatase TiO2 System Evaluated with the B2PLYP Double Hybrid Functional

The electronic properties of anatase titanium dioxide (TiO2) materials are of paramount importance for photocatalytic application. Ab initio calculation is performed on anatase TiO2 with various cluster sizes and shape, using Gaussian 09 program employing the standard 6-311G(d) and 3-21G basis set. Hartree-Fock (HF) theory, exchange-functional of density functional theory including hybrid (B3LYP, B3PW91, PBE1PBE and PBEh1PBE) and double-hybrid (B2PLYP), together with 2nd order Møller-Plesset perturbation theory are used to predict the band gap energy of anatase TiO2. With the inclusion of long-range HF exchange, double hybrid B2PLYP functional is able to predict band gap energy value (3.06 eV) which as compared to the experimental value (3.20 eV). Besides, this double hybrid exchange-correlation functional shows good compromise by obtaining an accurate description for cohesive energy of anatase TiO2. Thus, double-hybrid B2PLYP functional is suggested to be a practical choice for predicting the electronic properties for anatase TiO2.

Predictive study, using density functional theory and time dependent functional theory, on the structure-property quantification of methylene blue and methyl red dyes for the application in organic solar cells

In this work, two organic materials as dyes, namely, methylene blue (MB) and methyl red (MR), have been proposed to play the role of the electron donor in organic photovoltaic (OPV) cells. We use the PCBM as a well-known electron acceptor. The density functional theory (DFT) method has been used to determine the electrostatic potential and the frontier molecular orbitals (FMO), of the methylene blue (MB) and the methyl red (MR) compounds. Nonlinear optical (NLO) descriptors have been determined for the two compounds. The potential energy surface analysis has been performed by the DFT method using the exchange and correlation of Becke, Lee, Yang, and Parr Gradient Corrected Functional (B3LYP) with the standard 6-31G(d) base. We have performed another theoretical study using quantum time-dependent density functional theory (TD-DFT) on both MB and MR as organic dyes to determine their UV-Vis spectra. The results of the energy gap, chemical hardness, dipole moment, and hyperpolarizability show that MB may be chemically more reactive Than MR. The present work has proposed a bilayer organic photovoltaic (OPV) cell to contribute to the valorization of the two dyes as solar materials. The developed photovoltaic cell project has used electrical and energetic parameters that can describe the OPV cell based on ([MB or MR]: PCBM). Open-circuit voltage (Voc), excitation energy, and oscillator strength have been theoretically determined. The results of the present work showed a remarkably high open circuit voltage, especially in the case of methyl red (1.55 V) more than in the case of the methylene blue (0.84 V) so that both of the two dyes can be a good candidate for organic solar cells.

Hantzsch Ester-Mediated Visible-Light-Induced Radical Ethoxycarbonyldifluoromethylation of Aryl Alkynes: Kinetic-Controlled Stereoselective Synthesis of Z-gem-Difluoroallyl Esters.

A kinetic-controlled photocatalyst-free visible-light-induced stereoselective synthesis of α,α-gem-difluoro-Z-allyl esters was succeeded at room temperature in moderate to excellent yields with up to Z-isomer-only stereoselectivities through a reductive radical ethoxycarbonyldifluoromethylation of terminal aryl alkynes with blue LED (465 nm)-excited Hantzsch ester. The geometry optimizations obtained by the DFT/B3LYP calculation with a standard 6-31G(d,p) basis set were also employed for the mechanism study on the formation of a key α,α-difluoroallyl ester radical intermediate, which was generated from the addition of the ethoxycarbonyldifluoromethyl radical to aryl alkyne substrates and the stabilization effect of the neighboring group. Subsequent steric hindrance-determined hydrogen generated from the Hantzsch ester radical cation led to the formation of final aryl-substituted Z-difluoroallyl esters. This methodology provided convenient access to the synthetically important Z-configured gem-difluoroallylic building blocks.

Combined experimental and theoretical investigations on 9-[3,4-dihydroxy-5-(hydroxymethyl)oxolan-2-yl]-1,9-dihydro-6H-purin-6-one 4-nitrophenol (IPNP) molecule

Inosine and p-nitrophenol were taken in equimolar ratio to synthesize 9-[3,4-dihydroxy-5-(hydroxyme-thyl)oxolan-2-yl]-1,9-dihydro-6H-purin-6-one 4-nitrophenol via solvent vaporization technique. The synthesized material was subjected to single-crystal X-ray diffraction analysis, which confirms that it is crystallized in a monoclinic crystal system with space group P21. Hirshfeld analysis showed that molecule had close contacts of O···H/H···O, amounting to 45.7%, observed over dnorm surface with red spots owing to intermolecular hydrogen bonding. 1H NMR and 13C NMR analysis confirmed the structure of the IPNP molecule. The signal at δ 162.82 ppm confirmed the presence of hydroxyl group attached carbon in p-nitrophenol. FTIR spectroscopy confirmed the presence of all functional groups in the molecule. The broad band at 3334 cm−1 is due to OH stretching and the strong peak at 1694 cm−1 is owing to NO stretching. Density functional theory calculations performed by Becke-3-Lee-Yang-Par (B3LYP) level and M06-2X, combined with the standard 6-31G (d,p) basis set on IPNP molecule correlated well the with experimental data. UV-Vis spectrum showed absorption at 244 and 318 nm, which are due to n→π* and π→π* transition in the molecule. The HOMO-LUMO energy gap was 4.561 eV. A fluorescence peak was observed at 385 nm with an energy gap of 3.21 eV via photoluminescence spectroscopy. The antibacterial activity tests indicated that IPNP inhibited both Vibrio alginolyticus and Staphylococcus aureus bacteria.

Effect of hydrogen bonds and CF3 group on the regioselectivity and mechanism of [3 + 2] cycloaddition reactions between nitrile oxide and 2,4-disubstitutedcyclopentenes. A MEDT study.

The mechanism and the regioselectivity of the non-polar [3 + 2] cycloaddition reactions between nitrile oxide and two cyclopentenes were theoretically investigated within the molecular electron density theory (MEDT) using DFT methods, namely the B3LYP, MPWB1K and ωB97XD functionals together with the standard 6-31G(d) basis set. The activation energies of these 32CA reactions are relatively high, due to the low nucleophilic power of both cycloalkenes and the relatively moderate electrophilic nature of the nitrile oxide. The B3LYP and MPWB1K functionals reproduced high relative energies values, while the ωB97XD one yields better values in the kinetic and thermodynamic energies. The completely 4-regioselectivity that observed experimentally has been explained by the analysis of the relative energies, in which the formation of 4-regioismeric cycloadducts is always the more kinetically favored one. The electron localization function (ELF) topological analysis showed that the studied 32CA reactions proceed through two-stage one-step nonconcerted mechanism. The effects of the hydrogen bonds on the regioselectivity determination have been investigated by mean both noncovalent interactions (NCI) and quantum theory of atoms in molecule (QTAIM) analyses, which confirm the presence of high strength N - H···O hydrogen bond and a supplementary weak stabilized H…F hydrogen bonds.

Crystallography and DFT Studies of Synthesized Tetraketones.

Two tetraketone derivatives, one previously reported and one novel, were synthesized, whose structures have been confirmed by elemental analyses, NMR, HPLC-MS, and IR spectroscopy. The crystal structures of synthesized tetraketones were determined using X-ray single-crystal diffraction. To analyze the molecular geometry and compare with experimentally obtained X-ray crystal data of synthesized compounds 1 (2,2'-((4-nitrophenyl)methylene)bis(5,5-dimethylcyclohexane-1,3-dione)) and 2 (2,2'-((4-hydroxy-3-methoxy-5-nitrophenyl)methylene)bis(5,5-dimethylcyclohexane-1,3-dione)), DFT calculations were performed with the standard 6-31G*(d), 6-31G**, and 6-31+G* basis sets. The calculated HOMO-LUMO energy gap for compound 1 was 4.60 eV and this value indicated that compound 1 is chemically more stable compared to compound 2 whose energy gap was 3.73 eV. Both compounds' calculated bond lengths and bond angles were in very good accordance to experimental values determined by X-ray single-crystal diffraction.

Molecular Structure, Vibrational Spectral Studies, NLO Properties and frontier molecular investigations of 2-Chloro-6-Fluoro Benzaldehyde by DFT

Benzaldehyde and its derivatives are the simplest in aromatic aldehydes and have wide range of use in different industries. Due to this reason, there exist a vast field of study of substituted benzaldehydes. Quantum mechanical calculations of geometries, energies, vibrational wave numbers and thermodynamic constants have been performed with Gaussian 09 program package using the beece-3-Lee-Yang-Parr- (B3LYP) functional supplemented with the standard 6-31G (DP). The optimized geometrical parameters obtained by computational methods. The thermodynamic properties as heat capacity, entropy and enthalpy of the titled compounds are derived also dipole moment, Polarizability and hyperpolarizability are calculated along with brief study of HOMO-LUMO is done.

Structure of Biologically Active Benzoxazoles: Crystallography and DFT Studies

Using X-ray single crystal diffraction, the crystal structures of biologically active benzoxazole derivatives were determined. DFT calculation was performed with standard 6-31G*(d), 6-31G** and 6-31+G* basis set to analyze the molecular geometry and compare with experimentally obtained X-ray crystal data of compounds. The calculated HOMO-LUMO energy gap in compound 2 (2-(2-hydroxynaphtalen-1-yl)-4-methyl-7-isopropyl-1,3-benzoxazol-5-ol) is 3.80 eV and this small gap value indicates that compound 2 is chemically more reactive compared to compounds 1 (4-methyl-2-phenyl-7-isopropyl-1,3-benzoxazol-5-ol) and 3 (2-(4-chlorophenyl)-4-methyl-7-isopropyl-1,3-benzoxazol-5-ol). The crystal structures are stabilized by both intra- and intermolecular hydrogen bonds in which an intermolecular O-H⋅⋅⋅N hydrogen bond generates N3 and O7 chain motif in compounds 1, 2, and 3, respectively. The calculated bond lengths and bond angles of all three compounds are remarkably close to the experimental values obtained by X-ray single crystal diffraction.

Effects of Substituent and Temperature on the Electronic Properties and Thermodynamics Parameters of 1-(Benzothiazolylamino) Methyl-2-Naphthol: A Computational Study

The effects of substituent and temperature on the 1- (benzothiazolylamino) methyl - 2- naphthol molecules were studied at CAM-B3LYP/6-311G (d,p) level of theory. Selected substitutions were NH2, OH, Me, F, Cl, CHO, COOH, CN and NO2. Substituent effect on the frontier orbitals energies, HOMO-LUMO gap, chemical potential, and electrophilicity were explored. Dependencies of energy changes, reactivity properties and thermodynamics parameters (G, H and S) on the Hammett's constants (p) were provided. Thermodynamics parameters values of the formation reaction were studied reaction at 100-1000 K range. Computational investigation of the substituents and temperature influences on the formation reaction of the 1-(benzothiazolylamino) methyl-2-naphthol showed the negative E values in the studied reactions. Calculated dipole moment values reveal the presence of the EWGs induced a larger dipole moment compared with the EDGs. Higher negative values were found in the presence of EWGs compared to EDGs. Frontier orbitals were stabilized in the presence of EWGs. However, frontier orbitals were destabilized in the presence of EDGs. Thermodynamic analysis revealed that these reactions were non-spontaneous and exothermic. The G and negative H values were increased with increasing the temperature. Optimization and vibrational analysis were done with Gaussian 09 software package. The standard 6-311G(d,p) basis set was considered for the elements, respectively. CAM-B3LYP functional was used for the optimization of the geometries of the compound . This functional is Handy and coworkers’ long range corrected version of B3LYP using the Coulomb-attenuating method The identities of the optimized structures as an energy minimum were confirmed by vibrational analysis

Understanding the regioselectivity of the copper(I)- and ruthenium(II)- catalyzed [3 + 2] cycloadditions of azido derivative of ribose with terminal alkyne: a theoretical study

In the present work, the uncatalyzed, the copper(I)-catalyzed and the ruthenium(II)-catalyzed [3 + 2] cycloadditions (32CA) of azido derivative of ribose with terminal alkyne leading to 1,4- and/or 1,5- 1,2,3-triazole regioisomers have been studied at the B3LYP level of theory in combination with the LanL2DZ basis set for Cu, Ru and Cl atoms and the standard 6-31G(d) basis set for other atoms. The obtained results reveal that the uncatalyzed reaction requires high and similar activation energies, namely 18.29 and 18.80 kcal/mol for the 1,4 and 1,5 regioisomeric pathways, respectively, indicating a very limited regioselectivity in agreement with the experimental outcomes. Interestingly, for the copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC), investigated using the Fokin stepwise mechanism involving two copper atoms, the 1,4 regioisomeric reaction path found to be kinetically more favored than the 1,5 regioisomeric reaction path by 9.13 kcal/mol. By contrast, for the ruthenium(II)-catalyzed azide–alkyne cycloaddition (RuAAC), investigated using the Fokin mechanism using the pentamethylcyclopentadienyl ruthenium chloride [Cp * RuCl] complex, the 1,5 regioisomeric reaction path is more favored than the 1,4 regioisomeric reaction path by 3.48 kcal/mol. The present work puts in evidence the determinant role of Cu/Ru catalysts in the regioselectivity of this click reaction.

DFT calculations on molecular structure, MEP and HOMO-LUMO study of 3-phenyl-1-(methyl-sulfonyl)-1H-pyrazolo[3,4-d]pyrimidine-4-amine

Electronic structure calculation explores the molecular structure and geometric conformations of the molecules from only the knowledge of its constituent atoms. In the present work, quantum mechanical calculations of a 3-phenyl-1-(methyl-sulfonyl)-1H-pyrazolo[3,4-d]pyrimidine-4-amine molecule have been performed by Density Functional Theory using the standard 6-31G** basis set with the GAUSSIAN09. The electronic structure, dipole moment, frontier orbitals energy, thermal parameters (entropy, enthalpy, internal energy, and Gibb’s potential), Infrared (IR) spectral lines of the title molecule are elaborated. To study the chemical reactivity; molecular electrostatic potential (MEP) surface, HOMO-LUMO surface, and some other properties of the molecule were also investigated.

Ab Initio Study of TEPA Adsorption on Pristine, Al and Si Doped Carbon and Boron Nitride Nanotubes

The present first principles study entails the adsorption behavior of N, Nʹ, Nʺ-triethylenephosphoramide (TEPA) drug over the pristine, Si- and Al-doped (5, 5) armchair single-wall carbon and boron-nitride nanotubes (SWCNTs and SWBNNTs). Density functional theory (DFT) calculations were done via the B3LYP and M06-2X methods with the standard 6-31G** basis set. The results show that the adsorption of TEPA drug molecule occurred physically on pristine CNT and BNNT and chemically on Al- and Si-doped CNTs and BNNTs. Although Si- and Al-doped CNTs and Al-doped BNNT provide stronger adsorption, the change in the energy gap of the Si-doped BNNT was more pronounced. The lipophilicity calculations indicated that the pure, Si- and Al-doped BNNTs are better candidates for increasing the efficiency of TEPA drug. It has been predicted that the Si-doped BNNT may be a promising drug delivery agent.

DFT STUDY OF [2+2] CYCLOADDITION REACTIONS BETWEEN KETENE AND THIOKETONE DERIVATIVES

In this work, we study the cycloaddition reactions [2+2] between ketenes 1a-c ; 1a’-c’ and thioketones 2a-c ; 2a’-c’. using DFT (density functional theory) calculation method with B3LYP functional and the standard basis set 6-31G*. We discuss from thermodynamic and frontier orbitals point of view, the possibility and the regioselectivity of these reactions.

Comparative Analysis of Molecular Structure, Vibrational Spectral Studies and Nlo Properties of 3-Hydroxy-4methoxy-Benzaldehyde and 4-Hydroxy-3-Methoxy-Benzaldehyde by DFT

Benzaldehyde is best known as being artificial essential oil of almond and it has many other uses such as; the manufacturing of dyes, perfumes, flavourings, cinnamic and mandelic acids, and it is also used as a solvent. Some more recent developments in the use of benzaldehyde are for the health and agriculture industries. Due to these basic reasons there exist a vast field of study of substituted benzaldehydes. In the present study a comparative analysis is done between 3-hydroxy-4-methoxy-benzaldehyde and 4-hydroxy-3-methoxy-benzaldehyde. The spectral studies were performed for FTIR, IR (KBr and Nuzol) and Raman. Quantum mechanical calculations of geometries, energies, vibrational wave numbers and thermodynamic constants have been performed with Gaussian 09W program package using the Becke-3Lee-Yang-Parr (B3LYP) functional supplemented with the standard 6-31G (DP). The optimised geometrical parameters obtained by computational method used shows good agreement with the experimental data. The thermodynamic properties as heat capacity, entropy, enthalpy and Gibb’s free energy of the titled compounds at different temperatures were also calculated along with dipole moment, polarisability and hyperpolarisability.

First-principles study on vibrationally resolved fluorescence of fused 5,15-(diphenyl)-10,20-(dibromo)porphyrin molecule.

The vibrationally resolved fluorescence spectrum of a narrow-line single-molecule transducer, fused 5,15-(diphenyl)-10,20-(dibromo)porphyrin (fused-H2P) molecule, has been calculated by time-dependent density functional theory with the inclusion of both Franck-Condon and Herzberg-Teller contributions. Analytical transition dipole derivatives are used for the calculations of Herzberg-Teller terms to eliminate the possible errors caused by numerical differentials. The performance of different exchange-correlation functionals including B3LYP, ωB97X-D, and M06-2X has been examined. The comparison with the high-resolution experimental emission spectrum indicates that all three functionals can satisfactorily describe the fluorescence spectral profile, while ωB97X-D and M06-2X give slightly better excitation energy than B3LYP. Detailed analysis shows that the fluorescence spectrum is dominated by the Franck-Condon contribution, while the Herzberg-Teller term contributes mostly to its low energy tail. It is found that the size of the basis set has limited influence on the fluorescence spectrum, and a standard 6-31G(d, p) basis set is adequate for the purpose. The substitution of terthiophene side chains is found to have minor effects on the fluorescence spectrum. Our study provides unambitious assignments for all the vibronic structures in the experimental spectrum.

Spectral and quantum mechanical study of some azo-derivatives

Three azo-derivatives: 2, 2′-Dihydroxyazobenzene (DHAB), Sudan Orange G (SOG) and 4-(Phenylazo) diphenylamine (PDA) were studied in this paper from quantum-mechanical and spectral point of view. The nature and the contribution of the intermolecular interactions to the spectral shifts in the solutions of the studied azo-derivatives were established based on the existent theories. Some electro-optical parameters of the studied molecules were calculated with Spartan 14 software using Density Functional Theory (DFT) employing the B3LYP model and the standard 6-31G* basis set. The polarizability and dipole moment in the excited states were estimated considering the variation of the angle between dipole moments in electronic states giving the visible absorption band.

Density functional efficiency in the calculations of vibrational frequencies and molecular structures of β-diketones

Density functional theory (DFT) levels are employed to calculate the vibrational frequencies and geometrical data of β-diketones. We evaluate the relative performance of the different levels by comparing theoretical results to experimental values. The applied DFT levels in this work are B3LYP, BLYP, B3P86, B3PW91, BPW91, G96LYP, BP86, and G96PW91 with the standard 6-31G, 6-31G*, 6-31G**, 6-31+G**, 6-31++G**, 6-311G**, 6-311++G** basis sets. The best results are obtained at the B3LYP, B3PW91, and B3P86 levels.

Theoretical study on the polarizability properties of liquid crystal in the THz range

Terahertz (THz) technology developed rapidly in recent years. Liquid crystals (LCs) are one of the most promising base materials to construct switchable devices in THz range because of their high optical anisotropies. However, the practical applications of the devices are hampered by the relationships between birefringence, thickness and LCs switching time. Due to the long wavelength, THz device requires a larger birefringence LC than the device operated at optical frequencies. Yet, in order to design an efficient switchable LC-THz device, it is crucial to find or synthetize LC material which will still display a useful birefringence at THz frequencies. The birefringence properties of LC are determined by the molecular polarizability of the relevant material. Knowledge of the LC molecular polarizability and its dependence on the molecular structure is important for designing LC molecules with desired THz properties. The prediction of the photoelectric characteristics could save a considerable quantity of the man-power and materials needed for the design or synthesis of new LC compounds. A priori screening of materials and the prediction of the optoelectronic properties would make a vast opportunity for expanding the LC material application scope. Hence, the main purpose of the present work is to provide a theoretical method of calculating and analyzing the THz polarizability properties of LC single compounds for LC-THz device applications. In this work, the frequency dependent molecule polarizability values of liquid crystal PCH5, 5CB and 5OCB in THz range are calculated by the density functional theory method. The geometries of the studied LCs are optimized at B3 LYP levels with the standard 6-311G(d) basis set. From the optimized geometries the molecule THz polarizabilities of LCs are calculated by the M06-2x functional with 6-311++G(2d, p) basis set, and they are found to be in good agreement with experimental data. By plotting the polarizability density analysis (PDA), the spatial contributions of electrons to the longitudinal polarizability are presented. The influences of alkyl chain and core structure on the microscopic polarizability of the LC molecule are investigated and explained by using the finite field approach and PDA. The results show that the unsaturated group, such as benzene ring or cyanobenzyl, makes great contribution to the polarizability of LC. In the design process, the new type of LC molecule must be extended the length of up electron conjugated system, to reduce the energy gap between HOMO and LUMO, and hence improving LC molecule polarizabilty. We hope that the present work could give a useful guide in screening or designing LC molecules for THz applications, and offer an effective way to understand fundamental optoelectronic characteristic of LC materials in the THz frequency range.

Restoring rotational invariance of Löwdin populations

A decade ago it has been realized that Lowdin populations (atomic populations calculated in a Lowdin-orthogonalized basis) are not rotationally invariant if one uses Cartesian d- (f-) basis orbitals, as is the case for the standard 6-31G* or 6-31G** basis sets. It was shown that the reason for this behavior is that invariance is conserved only if the rotation induces a unitary transformation of the basis orbitals on each atom. Davidson pre-orthogonalizes the basis on every atom separately; then the rotational invariance is restored, but the numbers change wildly. Here the “best compromise” is proposed, in which one pre-orthogonalizes only those basis orbitals that transform between each other during the rotation. In this manner, the rotational invariance is restored and the numbers remain close to the range obtained by the conventional Lowdin-orthogonalization. It is also demonstrated that the situation with Wiberg indices (bond orders in the Lowdin-orthogonalized basis) is the same as for the populations: the condition of the invariance is the unitary character of the transformations induced by the rotations. In their case, the partial pre-orthogonalization proposed here is adequate, too.