Integral Equation Formalism Polarizable Continuum Research Articles

Exploring the impact of heterocyclic bridges for tuning the amplitudes of Nonlinear optical properties under Gas, IEFPCM and COSMO solvent models

Nonlinear optical (NLO) materials are a distinctive class of materials due to their NLO response and wide range of applications. We present a systematic quantum chemical study for designing triphenylamine based derivatives (1Ph to 3PhDTDZ) by modifying central bridge with various size and types of heterocyclic rings. Density functional theory (DFT) method is used to calculate the NLO properties including linear and third-order NLO polarizabilities (α and γ) by using M06-2X functional coupled with the 6-311G** basis set. The calculation results predict that among the designed compounds, 1PhDTDZ has the highest third-order NLO polarizability of 2347.7 x 10−36 esu and lowest transition energy of 1.828 eV. On the other hand, 3PhDTDZ has a greater amplitude (108.5 x 10−24 esu) of static linear polarizability (αiso). We also computed frequency-dependent third-order NLO polarizability values at various laser wavelengths (1500 nm to 1970 nm). This provides valuable information about the complex interaction between light and matter. Dynamic second hyperpolarizability of electro-optic Pockels effect (EOPE effect, (γ (−ω; ω,0,0)) is calculated at 1500 nm laser wavelength with a larger γ-amplitude of 36708.4 x 10−36 esu. The effect of solvent on α and γ has also been the primary focus of this research. An extensive solvation impact has been studied using integral equation formalism Polarizable Continuum Model (IEFPCM) and Conductor-like Screening Model (COSMO). Magnitudes of αiso and 〈γ〉 have shown variation from gas to solvent methods. While among solvents, amplitudes are seen 3.87 % to 11.29 % greater under the effect of COSMO-methanol than PCM-methanol. The Frontier molecular orbital (FMO) studies found a significant decrease in energy band gaps from 5.75 eV to 2.98 eV. Since our systems exhibit remarkable photovoltaic properties, they can be used as dye-sensitized solar cells (DSSCs). Their open circuit voltage (VOC) ranging from 1 eV to 4 eV. Thus, our designed triphenylamine based derivatives with distinct central heterocyclic bridges showcase remarkable efficiency as NLO materials, with additional benefits of exhibiting good photovoltaic properties.

Theoretical studies for the detailed electronic structure of organotin(IV) derivatives of 4-fluoroanthranilic acid, X-ray structure of n-dibutyltin bis(4-fluoroanthranilate)

The present study describes the detailed DFT-based electronic structure calculations without any symmetry constraints being performed on di- and triorganotin derivatives of 4-fluoroanthranilic acid (AFA), viz. Me2SnL2 (1), n-Bu2SnL2 (2), Me3SnL (3), and Ph3SnL (4) (where L= monoanion of AFA). The structural and atomic charge analysis have confirmed the previously reported our experimental results, i.e. bicapped tetrahedral and distorted tetrahedral geometry for di- and triorganotin derivatives, respectively, and all the complexes 1–4 contain a positively charged central tin atom surrounded by a negatively charged system. The single crystal X-ray structure of complex 2 (n-Bu2SnL2) also suggests that AFA acts as a monoanion and bidentate ligand resulting a bicapped tetrahedral environment around tin. Various population analysis such as Mulliken (MPA), Hirshfeld (HPA), and natural population analysis (NPA) have been employed to calculate the charges at all the atoms. A finite difference approximation method has been used to explain the charge distribution within the studied complexes 1–4 based on the conceptual global and local reactivity DFT-based descriptions, frontier molecular-orbital analysis (FMOA), and molecular electrostatic potential maps (MEP). Further, the conceptual DFT-based global reactivity descriptors and frontier molecular orbital analysis show that the interactions between CT-DNA and complexes 1–4 may be groove binding or electrostatic. The integral equation formalism-polarizable continuum model (IEF-PCM) has been employed to calculate the UV–visible spectra of 1–4 in the solvent field, whereas the same in the gas phase has been obtained with the help of time-dependent DFT (TD-DFT) at the same level of theory. The intramolecular charge distribution in 1–4 has been investigated with the help of natural bond orbital (NBO) analysis. The topological and energetic parameters at the selected bond critical points in the coordination sphere of complexes 1–4 have been calculated using atoms-in-molecules (AIM) theory. The analysis of different kinds of non-covalent interactions (NCI) in complexes 1–4 has also been investigated.

Chemical reactivity and regioselectivity investigation for the formation of 3,5-disubstituted isoxazole via cycloaddition [2 + 3] and antitrypanosomal activity prediction

The antitrypanosomal activity of 3,5-disubstituted isoxazole has been investigated through molecular docking, revealing its binding to Plasmodium falciparum through seven hydrogen interactions demonstrating high affinity, supported by Molecular Dynamics Simulations. Followed by the Quantum Theory of Atoms in Molecules (AIM) studies, confirming the strength of hydrogen bonds and an acceptable ADMET profile has been found. The chemical reactivity of the cycloaddition [3 + 2] has been explored using Density Functional Theory (DFT). Results revealed a reverse electron demand, which was confirmed by global reactivity indices. Electron displacement was investigated based on Fukui functions, Methyl Cation Affinity (MCA), Methyl Anion Affinity (MAA), and Molecular Electrostatic Potential (MEP). The regioselectivity of the reaction was explored in the gas phase first and in dichloromethane secondarily to assess their impact on the reaction using the Integral Equation Formalism Polarizable Continuum (IEFPCM) model. Finally, additional bioactive compounds with 3,5-disubstituted isoxazole properties have been found using screening methods.

Molecular structure, electronic properties, spectroscopic, quantum computational studies of 1-(4-hydroxy-3-methoxyphenyl)ethanone-effective anticancer medicine

The molecular structure of 1-(4-hydroxy-3-methoxyphenyl) ethenone has been optimized, and its various parameters were ascertained, using Density Functional Theory. The molecule’s Fourier Transform-Infra Red and Raman spectra are recorded and examined. By comparing the computational and experimental results, molecular structure, bond length, and vibrational band intensity were all interpreted. The Integral Equation Formalism polarizable continuum model’s depictions of electronic and Frontier Molecular Orbital solvent interaction investigations are sported to perceive the charge transfer among the atoms of the molecule in eco-green solvents such as water, acetone, and ethanol. The reactivity sites can be studied by locating and charting the electron density on the surface. The compound’s hardness, softness, electrophilicity, and ionization potential were all analyzed. The pharmacological effects and intra-molecular hyper conjugative interactions are liable for its molecular stability, as shown by Natural Bond Orbital research. Topological studies, including Electron Localized Function, Localized Orbital Locator, and Reduced density gradient analysis, were performed to locate the compound’s bonding area and Vander Waals interactions. Urea was used as a reference compound to examine the substance’s non-linear optical characteristics. Total Density of States has investigated the role of molecular orbitals. Drug-likeness, a Ramachandran plot, and molecular docking were also performed to further analyze 1-(4-hydroxy-3-methoxyphenyl) ethanone’s biological activity. The docking results lend credence to the idea that the title compound could function as a powerful cancer treatment.

Effect of solvent role in electronic properties, band gap, electron injection barrier, charge transport nature, topology studies (ELF, LOL, RDG), and optical properties of azoles for multifunctional applications

The ground state geometries of oxazole compounds, i.e., 3,5-Bis-(4-chloro-phenyl)-7a-methyl-dihydro-oxazolo[3,4-c]oxazole (Compound1) and 3,5-Bis-(4-methoxy-phenyl)-7a-methyl-dihydro-oxazolo[3,4-c]oxazole (Compound2) were optimized using Density functional theory employing B3LYP/6-31G++ level for comparing the geometric parameters (torsion angles, bond angles & bond lengths) with the X-ray crystallographic information. We explored the charge transport nature, wave functional properties, optical and electronic properties of both the oxazoles. The computed geometric parameters are rational to the experimental data. The time-domain TD - B3LYP/6-31G++ & the B3LYP/6-31G++ levels were used to reveal the electronic characteristics and absorption wavelength. Intra-molecular charge transfer was perceived in studied compounds. The IEFPCM (Integral Equation Formalism Polarizable Continuum Model) model was used to calculate the solvation UV spectrum. The effect of various solvents (acetone, acetonitrile, DMF(Dimethylformamide), DMSO (Dimethyl sulfoxide) and methanol) was examined on the excitation energies but solvent polarity has no discernible impact on the wavelengths of absorption. From HOMO-LUMO (Highest Occupied Molecular Orbital – Lowest Unoccupied Molecular Orbital) orbitals with various solvent molecules, band gap energies with the solvation effect are determined. Additionally, through the use of topological analytics like RDG (Reduced Density Gradient), ELF (Electron Localisation Function) & LOL (Localised Orbital Locator), the energy concentration of electrons was elucidated. Furthermore, the outcome of electron-donating cluster (–OCH3) and electron-withdrawing cluster (–Cl) was studied on open-circuit voltage, bandgap alignment, electron coupling constants, excitons dissociation values, ΔGinject – electron injection, LHE-Light Harvesting Efficiency and electron coupling constants (|VRP|).

Tailoring the band-gap, optical and fluorescent properties of 3,5-diaminobenzoic acid via functionalization with chemical groups: A DFT study

3,5-diaminobenzoic acid (3,5-DABA) with chemical formula C7H8N2O2 was functionalized with CH3-, OH-, NH2- and NO2- to obtain: CH3-3,5 DABA, OH-3,5 DABA, NH2-3,5DABA and NO2-3,5DABA. These molecules were built with Gauss view 6.0 and their structural, spectroscopic, optoelectronic and molecular properties were investigated using density functional theory (DFT). B3LYP (Becke's 3-parameter exchange functional with Lee-Yang-Parr correlation energy) functional and 6–311+ G (d, p) basis set were used to understand their reactivity, stability and optical activity. Integral equation formalism polarizable continuum model (IEF - PCM) was used to calculate the absorption wavelength, energy required to excite the molecules and oscillator strength. Our results reveal that the functionalization of 3,5 DABA with the groups caused a decrease of the energy gap from 0.1563 eV, to 0.1461 eV, 0.13818 eV and 0.13811 eV in NO2-3,5DABA, OH-3,5DABA and NH2-3,5DABA respectively. The lowest energy gap of 0.13811 eV for NH2-3,5DABA is in good agreement with its highest reactivity value (global softness of 7.240). The most observed significant donor - acceptor NBO interactions where found to occur between *ΠC16-O17 → *ΠC1-C2, *ΠC3-C4→ *ΠC1-C2, *ΠC1-C2 → *ΠC5-C6, *ΠC3-C4 → *ΠC5-C6, *ΠC2-C3 →*ΠC4-C5 natural bond orbitals having second- order stabilization energies of 101.95 kcal/mol, 368.41 kcal/mol, 174.51 kcal/mol, 255.63 kcal/mol and 235.92 kcal/mol in 3,5-DABA, CH3-3,5-DABA, OH-3,5-DABA, NH2-3,5-DABA and NO2-3,5-DABA respectively. The highest perturbation energy was observed in CH3-3,5DABA while the lowest perturbation energy was observed in 3,5DABA. The absorption band of the compounds were observed in the order: NH2-3,5DABA (404 nm) > N02-3,5DABA (393 nm) > OH-3,5DABA (386 nm) > 3,5DABA (349 nm) > CH3-3,5DABA (347 nm).

Solvent effect on the self-association of the 1,2,4-triazole: A DFT study

The self-association of 1,2,4-triazole was studied by the DFT method at the B3LYP/6-311++G(d,p) level in the gas phase, and the most stable dimer and trimer were presented. Based on the integral equation formalism polarizable continuum model (IEFPCM), the effect of solvents such as water and dimethyl sulfoxide (DMSO) on the geometric parameters of molecular complexes (dimer and trimer), atomic charge distribution, molecular electrostatic potential (MEP) surface, and frontier molecular orbitals (FMO) was analyzed. Intermolecular interactions in cyclic and linear complexes were studied using topological analyses (QTAIM, NCI, RDG, ELF, and LOL). IR spectra of 1,2,4-triazole monomer, dimer, and trimer were simulated and compared with experimental results. In self-association, intermolecular hydrogen bonding causes a red shift of the N–H stretching vibrational frequency of 1,2,4-triazole. The solvent effect on the vibrational bands of monomer, dimer, and trimer was analysed.

Probing the water hydrogen-bonding effects on the ground and low-lying excited states of phenanthroline isomers

In this work, the ground and low-lying excited states of a series of phenanthroline isomers (1,10-phenanthroline, 1,7-phenanthroline, and 4,7-phenanthroline) were investigated. Density functional theory (DFT) was used for determining the structural and energetic properties connected to the ground state (such as bond lengths and angles, hydrogen-bond interactions, vibrational frequencies, and relative energies) of each molecule while time-dependent DFT was employed for probing the excited state parameters (excitation energies, oscillator strengths, and structures); both approaches were used in combination with the CAM-B3LYP exchange–correlation functional and the cc-pVTZ basis set. The computations were performed in the gas-phase and water. The effects originating from the interactions with the solvent environment were examined by means of the integral equation formalism polarizable continuum model (IEF-PCM), as well as using a composite solvation model (CSM) through the incorporation of explicit water molecules in combination with IEF-PCM. In terms of relative stability, 1,10-phenanthroline became the most stable isomer when the combined implicit-explicit solvation was taken into account, an interesting behavior that may be assigned to the existence of a chain of hydrogen-bond interactions involving the two explicitly added water molecules and both nitrogen atoms from 1,10-phenanthroline. This feature provided better stabilization to the system when compared to the 1,7-phenanthroline and 4,7-phenanthroline. Taking the 1,10-phenanthroline isomer as an example, all its low-lying singlet excited states were determined to have non-zero oscillator strengths when the CSM was used and, more importantly, one among these states was found as being highly accessible (with oscillator strength = 0.9545). From the comparison with the results obtained using solely the implicit solvation (IEF-PCM results), it is possible to assign the presence of the hydrogen-bond interactions as being an important factor for making such excited state likely to be accessed.

An Experimental and Computational Investigations on the Linear and Nonlinear Optical Characteristics of Novel Chalcone (E)-1-(4-(1H-imidazol-1-yl)phenyl)-3-(1, 5a1-dihydro pyren-1-yl)prop-2-en-1-one

A novel chalcone based pyrene (E)-1-(4-(1H-imidazol-1-yl)phenyl)-3-(1,5a1-dihydropyren-1-yl)prop-2-en-1-one (EIPDP) has been successfully synthesized by Claisen-Schmidt condensation reaction. The molecular structure was optimized using density functional theory (DFT) at B3LYP/ 6-311++G(d,p) basis set. In addition, molecular electrostatic potential (MEP) was obtained to study the intramolecular charge transfer (ICT) by introducing electrophilic and nucleophilic sites on the compound surfaces. Absorption UV-Vis spectra were performed experimentally and theoretically to study the electron transitions of the EIPDP. Further, the excitation states were characterized using the hybrid exchange-correlation functional of Coulomb Attenuated Method-Becke, 3-parameter, Lee-Yang-Parr (CAM-B3LYP) with the Integral Equation Formalism Polarizable Continuum Model (IEFPCM) in Dimethyl sulfoxide (DMSO) solvent at the same basis set. The nonlinear optical (NLO) properties were investigated using Z-scan techniques with continuous wave (CW) laser at 630nm. The NLO findings disclosed that the third-order nonlinear optical parameter (χ 3) for the title compound is in the order of 10−6 esu.

Exploring the water hydrogen-bonding effects on the ground and low-lying excited states of serotonin

In this work, we examined the ground and low-lying excited states of the serotonin (SERO) molecule and of four of its water hydrogen-bonded complexes (SERO-(H2O)n, with n = 1 and 2). Density functional theory (DFT) and its time-dependent variant (TD-DFT) were used for determining, respectively, ground state properties (such as equilibrium structures and relative energetics, when applicable) and excited state parameters (vertical excitation energies, generalized oscillator strengths (GOS), and structures). The CAM-B3LYP exchange–correlation functional with the def2-TZVP basis set was used and all the computations were performed in the gas-phase and in water (through the use of the integral equation formalism polarizable continuum model, IEF-PCM). In terms of ground-state, the existence of the H⋯O–H⋯N interaction in one of the SERO-H2O conformations contributed to the stabilization of the system when compared to its corresponding counterpart, with solvation decreasing (from 3.43 kcal/mol in the gas-phase to 1.75 kcal/mol in water) the differences regarding their relative energies. While no major differences regarding the excitation energies associated to an accessible state are suggested from the comparison between the results obtained for a given system through the consideration of solvation and those corresponding determined in the gas-phase, the hydrogen-bond interactions (originating from the explicit water molecules) combined with the implicit (water) solvation may be responsible for providing synergic effects in terms of increasing both the GOS related to a given open state as well as the number of excited states accessible, suggesting an enhancement in the photoabsorption. Taking one of the SERO-(H2O)2 conformations as instance, all the five lowest-lying excited singlets of the system were determined as being accessible (having GOS from 0.1036 to 0.5664) in water while only a single excited state (with GOS = 0.1150) is expected to be open in the gas-phase environment.

Using Solvation Free Energy as an Additional Parameter for Corrosion Inhibition Inspection of Organic Compounds in Acid Media: An Evaluation Study

The energies of frontiers molecular orbitals and derived electronic parameters are widely used to explain experimentally obtained inhibition effectiveness of several organic inhibitors against metallic corrosion. In this context, the present study aims to reevaluate the use of solvation free energy ( Δ G Solv ) as an additional parameter for the corrosion inhibition inspection. Three organic molecules set previously reported as corrosion inhibitors in acidic solutions were selected to conduct this in silico study. The solvation free energy in the aqueous phase of chosen inhibitors was determined using DFT-based calculations in combination with integral equation formalism-polarizable continuum solvation model. The acquired data show that Δ G Solv can be used together with other known parameters to inspect the inhibition performance of organic inhibitors in acidic media.

DFT-GIAO 1H and 13C-NMR Chemical Shifts Calculation of Uncaria longiflora Alkaloids

Recently, the structure elucidation of three new chiral alkaloids, namely isoformosaninol (1), formosaninol (2), and longiflorine (3), isolated from the leaves of U. longiflora var. pteropoda (Miq.) Ridsdale has been reported. Their molecular structures were initially determined by using experimental NMR data, following a systematic method for establishing the absolute configuration of pentacyclic oxindole alkaloids (POAs), and the chemical correlation method based on the known chirality of their precursor, secologanin. Indeed, the integration of the information from experimental and theoretical data can be of fundamental importance for the successful elucidation of the configurational and stereostructural assignments of organic compounds, including natural products. Thus, the present work was conducted to further support the success of this integration by focusing on the NMR data, which is the most critical spectroscopic analysis in the structural elucidation of natural products. The 1H and 13C-NMR chemical shift values for the three alkaloids were calculated using density functional theory-gauge including atomic orbitals (DFT-GIAO) approximation at the B3LYP/6-311+G(d,p) level of theory in integral equation formalism polarizable continuum model (IEF-PCM) concerning to tetramethylsilane (TMS). Statistical error analysis between the experimental and calculated supported an excellent correlation with linearity of higher than 93% and 99% for 1H and 13C-NMR chemical shifts, respectively, for the three alkaloids. The correct correspondences between experimental and calculated data sets were further supported by the mean absolute error (MAE) parameter. The present findings provide insights on the usefulness of integrating experimental and calculated NMR data to ascertain structural elucidation in easing ambiguity. 

Estimation of Dipole Moments of New Coumarin Dye by Experimental and Theoretical Methods

AbstractThe absorption and fluorescence emission spectra of coumarin dye, 4‐((4‐methoxyphenoxy) methyl)‐6‐methoxy‐2H‐chromen‐2‐one (4‐MPMMC) in different polarity solvents are recorded. The effects of solvent polarity on the spectral properties are discussed. It is found that, spectrum peak shifts toward higher wavelength, as the solvent polarity changes. The ground (µg) and excited state (µe) dipole moments are estimated using Lippert's, Bakshiev's, and Kawski‐Chamma‐Viallet's equations. The µe values are found to be higher than µg values for all solvents. This suggests that the dye is more polar in excited state than in ground state. Computational studies are done using Time Dependent Density Functional Theory (TD‐DFT), DFT, and Zindo methods with the help of Gaussian16W; Integral Equation Formalism Polarizable Continuum Model (IEFPCM). Further, the excited state dipole moments are estimated in different solvents and are compared with the experimental results. The reactive centers like electrophilic and nucleophilic sites are identified along with contour action using electrostatic potential (ESP) 3D map using DFT analysis.

Quantum chemical studies on structural, spectroscopic, nonlinear optical, and thermodynamic properties of the 1,2,4-triazole compound

AbstractIn this study, the structure of 4-[4-(diethylamino)-benzylideneamino]-5-benzyl-2H-1,2,4-triazol-3(4H)-one (DBT) was examined through spectroscopic and theoretical analyses. In this respect, the geometrical, vibrational frequency,1H and13C-nuclear magnetic resonance (NMR) chemical shifts, thermodynamic, hyperpolarizability, and electronic properties including the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) energies of DBT as a potential non-linear optical (NLO) material were investigated using density functional theory at the B3LYP level with the 6-311G basis set.1H and13C-NMR chemical shifts of DBT with the gauge-invariant atomic orbital and continuous set of gauge transformation methods (in the solvents) were estimated, and the computed chemical shift values displayed excellent alignment with observed ones. Time-dependent density-functional theory (TD-DFT) calculations with the integral equation formalism polarizable continuum model within various solvents and gas phases in the ground state were used to evaluate UV-vis absorption and fluorescence emission wavelengths. Thermodynamic parameters including enthalpy, heat capacity, and entropy for DBT were also calculated at various temperatures. Moreover, calculations of the NLO were carried out to obtain the title compound’s electric dipole moment and polarizability properties. To illustrate the effect of the theoretical method on the spectroscopic and structural properties of DBT, experimental data of structural and spectroscopic parameters were used. The correlational analysis results were observed to indicate a strong relationship between the experimental and theoretical results.

Theoretical Studies on the Oligomerization of Silicate Species in Basic Solution.

The possible reaction pathways of silicate species to linear- and ring-structure oligomers up to silicate hexamers in the basic medium have been studied using the density functional theory. The calculations were performed at the ωB97XD/6-31+G(d,p) level, and the integral equation formalism polarizable continuum model was employed to simulate the solvent effects, and it was found that they are appropriate in exploring the reaction mechanism of silicate species condensation. There are two steps in the anionic silicate condensation reactions: the SiO-Si bond formation step and the dehydration step. Moreover, the latter is the rate-limiting step for most of the reaction pathways except for the cyclization reaction of the linear pentamer to the 5-ring. The short linear oligomers would be likely formed from the reaction between monomers and oligomers, while the longer ones are easily formed through the reactions between short oligomers. The 4-ring and branched 5-ring oligomers are found to be formed very favorable both in kinetic and thermodynamic and could have great influences on the initial stage of zeolite synthesis. The intramolecular and intermolecular hydrogen bond effect of silicate species is an important factor affecting the reaction mechanism.

Quantum chemical analysis of hydrogen bonding in pyrrolidone dimers and pyrrolidone–water complexes

The structure of pyrrolidone dimers and hydrogen-bonded complexes of pyrrolidone with water molecules (1–3 molecules in complex) was studied by quantum chemical method on the basis of density functional theory (DFT) using three-parameter hybrid Becky-Lee-Yang-Parr functional and gradient-corrected correlation functional of Perdew, Burke and Ernzerhof (PBE) with D3 version of Grimme dispersion correction, Austin-Frisch-Petersson functional with dispersion correction (APFD) and augmented correlation-consistent polarized valence-only triple-zeta (aug-CC-pVTZ) basis set. The geometrical parameters of hydrogen bonds, binding energies, atomic charges based on Atomic Polar Tensors (APT) and vibrational frequencies were calculated and Natural Bond Orbital (NBO) and quantum theory of atoms in molecules (QTAIM) methods were used. The analysis was carried out for classic H-bonds and C-H…O. The calculations also were made taking into consideration the water medium with the integral equation formalism polarizable continuum model (IEFPCM).

Water hydrogen-bonding effects on the ground and low-lying excited states of dipyridyl isomers

In this work, we examined the ground and low-lying excited states of six dipyridyl isomers (2,2′-dipyridyl, 2,3′-dipyridyl, 2,4′-dipyridyl, 3,3′-dipyridyl, 3,4′-dipyridyl, and 4,4′-dipyridyl), emphasizing the effects that solvation (water) molecules have on properties such as ground state equilibrium structures, relative energies in terms of conformations and transition states (regarding possible cis–trans interconversions), vertical excitation energies (VEs), generalized oscillator strengths (GOS), and excited state structures. Density functional theory (DFT) and its time-dependent formalism (TD-DFT) were used for determining all the ground state and excited state properties, respectively, both being employed with the CAM-B3LYP exchange–correlation functional and the cc-pVTZ basis set. In addition, effects caused by interactions with the solvent environment were probed by means of using two different approaches: i) the integral equation formalism polarizable continuum model (IEF-PCM) and ii) a composite solvation model (CSM) through the incorporation of explicit water molecules in combination with the IEF-PCM. In general, a decrease in the relative energies regarding a given cis/trans counterpart is noticed when solvation is considered independently from the model used; all the dipyridyl cis/trans isomers became (practically) isoenergetical due to dipyridyl-H2O hydrogen-bonding interactions. Moreover, the interconversion barriers were also found to be lowered due to solvation effects. For instance, the energy barrier in terms of interconversion of the trans 2,2′-dipyridyl to the cis 2,2′-dipyridyl was determined as (approximately) 67 % of the corresponding value obtained in the gas-phase. Although no major differences regarding the values of the VEs associated to a bright state are suggested from the comparison between the results obtained for a given isomer through the consideration of solvation and those corresponding determined in the gas-phase, the GOS are all increased when solvation is considered, suggesting an enhancement in the photoabsorption of all the isomers when in presence of solvent. In addition and in contrast to what was seen previously in the case of the gas-phase, 4,4′-dipyridyl presented a bright state among the five lowest-lying excited singlets (accessible at the UVC energy region), which is located at 5.49 eV (with GOS = 0.4465) at the TD-DFT/CAM-B3LYP/cc-pVTZ level of theory in water (IEF-PCM) and at 5.47 eV (with GOS = 0.5331) at the same level of theory with the CSM. Given that no significant change was noticed in the optimized structures for the excited states, it is possible to infer that all the compounds will decompose through photo decomposition (chemical reaction occurring in the excited state) rather than direct photolysis when in solution.

Molecular interaction studies of hydrogen-bonded N-Methyl-2-Pyrrolidone /Ethanol binary mixtures by dielectric relaxation spectroscopy and their temperature dependence

Complex permittivity of the binary mixtures of N-Methyl-2-Pyrrolidone (NMP) with Ethanol (ETH) has been studied in the microwave frequency range at various temperatures. The binary liquid system NMP-ETH is selected to interpret the effect of carbonyl (-CO) group of NMP and hydroxyl group (-OH) of ETH on the volumetric, thermal and dielectric properties. The dipole moment (μ) and relaxation time (τ) is evaluated from Higasi's method and Havriliak-Negami equation. The excess molar volume (VmE), excess permittivity (εE), excess refractive index (nDE), excess inverse relaxation time (1/τ)E are fitted with the Redlich-Kister equation. The results obtained from Polarizable Continuum Model (PCM) and Integral Equation Formalism Polarizable Continuum Model (IEFPCM) solvation theories using DFT methods are correlated with the experimentally determined parameters. The molecular association and chemical stability of the system is interpreted in terms of single-point energy, HOMO-LUMO calculations. The existence of a hydrogen bond within the NMP-ETH system is confirmed from the FT-IR, UV–Vis's spectra.

Spectroscopic characterization and binding interaction of heavy metal onto the surface receptor of the azobenzene: DFT and experimental approach

The azobenzene 1-arylazo-2-naphthol has been synthesized and characterized by elemental analysis, 1H NMR, IR and UV–Vis spectroscopies using both experimental and theoretical methods. The MEP, NPA and FMOs have also been performed at the DFT/B3LYP-D3 level with different solvents in order to investigate the solvent's effect. The energetic behavior of the compound has been examined in the gas phase and in solvent media using the integral equation formalism polarizable continuum model (IEF-PCM). Solvents had sligth significant effect on NPA values whereas both molecules hardness and stability decrease along with increasing of the solvent's polarity. Vibrational and absorption analysis showed no significant azo±hydrazone tautomerism. Theorically, the title molecule calculated in Acetonitrile solvent is the most reactive. The observed red shifts are explained by the large extension of the π conjugated system and the blue shifts confirm the appearance of several tautomeric forms of the studied azo-benzene which lead to a marked improvement in photochemical stability. The cation binding properties of azo benzene as absorption sensor for Cu2+, Mg2+, Ni2+ and Zn2+ cations were reported. The highest adsorption energy in both gas and liquid phase corresponds to the complexes Azoic/Ni2+ then in Azoic/Cu2+ and somewhat in Azoic/Zn2+complex. The lowest adsorption energy is given to Azoic/Mg2+ complex. After cations chemisorption on azoic molecule a bathochromic shift is observed in the optical spectra, particularly for Azoic/Ni2+ complex, which is the proof of interaction between azoic compound and mentioned cations. The electronic proprieties and the vibrational spectra can therefore be used to detect the presence of different cations and the azobenzene shows appropriate properties to constitute good cations (Ni2+ and Cu2+) sensors.

Quantum chemical calculation of intrinsic reaction coordinates from trans to cis structure of fluvoxamine

Fluvoxamine is a selective serotonin reuptake inhibitor. Its trans-isomer [(E)-isomer] is pharmacologically active, whereas its cis-isomer [(Z)-isomer] loses its activity. It is a pharmaceutical interest whether the structural change from the (E)-isomer to the (Z)-isomer spontaneously occurs in aqueous solutions without ultraviolet (UV) irradiation. In the present study, the transition state of fluvoxamine was determined by quantum chemical calculation using density functional theory (DFT), and the intrinsic reaction coordinates (IRCs) from the (E)-isomer to the (Z)-isomer were calculated using UB3LYP/6-311++G(d,p) with the integral equation formalism-polarizable continuum model (IEF-PCM). The activation energy of isomerization from the (E)-isomer to the (Z)-isomer was estimated to be 55 kcal/mol. Further, the absorption spectra, the nuclear magnetic resonance chemical shift values, the Raman spectra and the infrared spectra were calculated for the (E) and (Z)-isomers obtained from the reaction coordinate calculation, and these results were in good agreement with the experimental values. The geometrical structures of the (E) and (Z)-isomers proposed in the present study can be used as theoretical models of fluvoxamine for molecular dynamics calculations in future.