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The present study aims at investigating, for the first time, the formation of tetrahedral intermediates during the equilibrium mechanism of D-glucaric acid in water. In this work, carried out at B3LYP/6-31+G(d,p) computational level in vacuum and using the polarizable continuum model, two systems are proposed and simulated: the first describes an intramolecular proton transfer, and the second requires the intervention of solvent molecules for the proton transfer. The second system, simulated in vacuum, indicates greater ease in establishing this equilibrium due to a significant reduction in angular tensions. Also, the idea of a tetrahedral intermediate carrying two geminal diol groups constitutes a favorable hypothesis due to the low energy barriers calculated as well as a better structural flexibility generated following the equilibrium of the tetrahedral intermediates between them. Experimental confirmation of the presence of such a powerful tetrahedral intermediate would be a considerable advance in resolving the equilibrium mechanisms of D-glucaric acid. [ABSTRACT FROM AUTHOR]

Optical absorption spectra of para-aminothiophenol in n-hexane and methanol solutions have been obtained. The calculation has been carried out using the TDDFT B3LYP/6-311+G(d,p) method taking into account the polarizable continuum model of the electronic spectra of the p-aminothiophenol molecule in n-hexane and its hydrogen-bonded complex with two methanol molecules in a methanol solution. Based on these calculations, the main absorption bands are interpreted and it is shown that the second excited singlet state is formed by a π → σ* electronic transition, which makes a significant contribution to the first absorption band of p-aminothiophenol in these solutions. [ABSTRACT FROM AUTHOR]

Polarizable continuum solvation models are popular in both, quantum chemistry and in biophysics, though typically with different requirements for the numerical methods. However, the recent trend of multiscale modeling can be expected to blur field‐specific differences. In this regard, numerical methods based on domain decomposition (dd) have been demonstrated to be sufficiently flexible to be applied all across these levels of theory while remaining systematically accurate and efficient. In this contribution, we present ddX, an open‐source implementation of dd‐methods for various solvation models, which features a uniform interface with classical as well as quantum descriptions of the solute, or any hybrid versions thereof. We explain the key concepts of the library design and its application program interface, and demonstrate the use of ddX for integrating into standard chemistry packages. Numerical tests illustrate the performance of ddX and its interfaces. This article is categorized under:Software > Quantum ChemistrySoftware > Simulation Methods [ABSTRACT FROM AUTHOR]

A possible mechanism is considered for the formation of nanoscale oxides based on titanium and aluminum isopropoxides in a medium of supercritical CO2 fluid. It is shown that because of intermolecular interactions and high pressure in the system, the supercritical fluid acquires the properties of a condensed medium, the main role of which is to restrain processes of hydrolysis. At the first stage of the hydrolysis of titanium isopropoxide, the water molecule is coordinated in the outer sphere of the central atom due to the formation of intermolecular hydrogen bonds. It is then coordinated into the inner sphere with the formation of a five-coordinate transition state and its destruction, creating a product substituted for the hydroxo group. The next steps proceed in a similar way. The described mechanism agrees with experimental findings and produces nanosized X-ray amorphous titanium oxide. (With aluminum isopropoxide, only the hydrolyzed hydroxo form can be produced.) Results suggest the production of nanosized oxides from isopropoxides in a medium of supercritical CO2 fluid is possible for transitional d-elements. [ABSTRACT FROM AUTHOR]

For the ground-state properties of gas-phase nanomolecules with multi-reference character, thermally assisted occupation (TAO) density functional theory (DFT) has recently been found to outperform the widely used Kohn–Sham DFT when traditional exchange-correlation energy functionals are employed. Aiming to explore solvation effects on the ground-state properties of nanomolecules with multi-reference character at a minimal computational cost, we combined TAO-DFT with the PCM (polarizable continuum model). In order to show its usefulness, TAO-DFT-based PCM (TAO-PCM) was used to predict the electronic properties of linear acenes in three different solvents (toluene, chlorobenzene, and water). According to TAO-PCM, in the presence of these solvents, the smaller acenes should have nonradical character, and the larger ones should have increasing polyradical character, revealing striking similarities to the past findings in the gas phase. [ABSTRACT FROM AUTHOR]

In this work, 242 NMR spin–spin coupling constants (SSCC) in 20 molecules are calculated, either with correlated wave function methods, SOPPA and HRPA(D), or with density functional theory based on the B3LYP, BHandH, or PBE0 functionals. The calculations were carried out with and without treatment of solvation via a polarizable continuum model in both the geometry optimization step and/or the SSCC calculation, and thereby, four series of calculations were considered (the full-vacuum calculation, the full-solvent calculation, and the two cross combinations). The results were compared with experimental results measured in a solvent. With the goal of reproducing experimental values, we find that the performance of the PBE0 and BHandH SSCCs improves upon including solvation effects. On the other hand, the quality of the B3LYP SSCCs worsens with the inclusion of solvation. Solvation had almost no effect on the performance of the SOPPA and HRPA(D) calculations. We find that the PBE0-based calculations of the spin–spin coupling constants have the best agreement with the experimental data. [ABSTRACT FROM AUTHOR]

Purely organic fluorescence emitters with ultrahigh exciton utilization, such as thermally‐activated delayed fluorescence (TADF) materials, are pursued as the cornerstone of the new‐generation organic light‐emitting diodes (OLEDs). However, most TADF emitters suffer from the dilemma of the aggregation‐caused fluorescence quenching effects, severely limiting their applications. Excitingly, the recently proposed aggregation‐induced delayed fluorescence (AIDF) strategy holds the potential to tackle this problem thoroughly. Here, the recently reported AIDF emitters CP‐BP‐PXZ and its halogenated counterparts, 3‐CCP‐BP‐PXZ and 3‐BCP‐BP‐PXZ, are investigated with a united theoretical and experimental insight. Based on first‐principles calculations combined with the polarizable continuum model (PCM) and the quantum mechanics/molecular mechanics (QM/MM) model, the photophysical mechanisms of these novel materials are proposed. It is found that both reverse intersystem crossing (RISC) and the subsequent radiative transition of CP‐BP‐PXZ are promoted via aggregation, owing to the increased effective RISC channels and boosted oscillator strength. Meanwhile, the unfavorable internal conversion rate is greatly slumped, ascribed to the suppressed Duschinsky rotation effect (DRE). The unique heavy‐atom effect is disclosed in 3‐CCP‐BP‐PXZ and 3‐BCP‐BP‐PXZ that the halogens act as steric blockers in crystal, rather than spin–orbit coupling enhancers. It is hoped that this work can shed new light on the designation of high‐efficient solid‐state fluorescence emitters. [ABSTRACT FROM AUTHOR]

The growing interest in tin-halide semiconductors for photovoltaic applications demands in-depth knowledge of the fundamental properties of their constituents, starting from the smallest monomers entering the initial stages of formation. In this first-principles work based on time-dependent density-functional theory, we investigate the structural, electronic, and optical properties of tin-halide molecules SnX n 2-n , with n = 1 , 2 , 3 , 4 ${n = 1,2,3,4}$ and X=Cl, Br, I, simulating these compounds in vacuo as well as in an implicit solvent. We find that structural properties are very sensitive to the halogen species while the charge distribution is also affected by stoichiometry. The ionicity of the Sn-X bond is confirmed by the Bader charge analysis albeit charge displacement plots point to more complex metal-halide coordination. Particular focus is posed on the neutral molecules SnX 2 , for which electronic and optical properties are discussed in detail. Band gaps and absorption onset decrease with increasing size of the halogen species, and despite general common features, each molecule displays peculiar optical signatures. Our results are elaborated in the context of experimental and theoretical literature, including the more widely studied lead-halide analogs, aiming to contribute with microscopic insight to a better understanding of tin-halide perovskites., (© 2024 The Authors. ChemPhysChem published by Wiley-VCH GmbH.)

For the ground-state properties of gas-phase nanomolecules with multi-reference character, thermally assisted occupation (TAO) density functional theory (DFT) has recently been found to outperform the widely used Kohn–Sham DFT when traditional exchange-correlation energy functionals are employed. Aiming to explore solvation effects on the ground-state properties of nanomolecules with multi-reference character at a minimal computational cost, we combined TAO-DFT with the PCM (polarizable continuum model). In order to show its usefulness, TAO-DFT-based PCM (TAO-PCM) was used to predict the electronic properties of linear acenes in three different solvents (toluene, chlorobenzene, and water). According to TAO-PCM, in the presence of these solvents, the smaller acenes should have nonradical character, and the larger ones should have increasing polyradical character, revealing striking similarities to the past findings in the gas phase.

In this work, 242 NMR spin–spin coupling constants (SSCC) in 20 molecules are calculated, either with correlated wave function methods, SOPPA and HRPA(D), or with density functional theory based on the B3LYP, BHandH, or PBE0 functionals. The calculations were carried out with and without treatment of solvation via a polarizable continuum model in both the geometry optimization step and/or the SSCC calculation, and thereby, four series of calculations were considered (the full-vacuum calculation, the full-solvent calculation, and the two cross combinations). The results were compared with experimental results measured in a solvent. With the goal of reproducing experimental values, we find that the performance of the PBE0 and BHandH SSCCs improves upon including solvation effects. On the other hand, the quality of the B3LYP SSCCs worsens with the inclusion of solvation. Solvation had almost no effect on the performance of the SOPPA and HRPA(D) calculations. We find that the PBE0-based calculations of the spin–spin coupling constants have the best agreement with the experimental data.

Aim. To perform a combined experimental and computational study on the luminescent properties of practically important class of organic dyes – 4-aminophthalimides. Results and discussion. The absorption and fluorescence spectra of 4-aminophthalimide derivatives in polar protic and aprotic solvents were computed and matched vs. the experimental data. The changes in emission spectra are mainly related to the NH2-group derivatization. The methyl substitution of amide hydrogen causes a batochromic shift of about 7 nm in the absorption peak and a negligible hypsochromic shift in the fluorescence peak, while introducing alkyl substituents to the amine moiety causes bathochromic shifts in absorption and emission peaks of 30 – 40 nm and 10 – 60 nm, respectively. Experimental part. Absorption and emission wavelengths were computed by the standard algorithm based on the ground state geometry optimization (equilibrium solvation), vertical excitation with nonequilibrium solvation, and the TD-DFT geometry optimization of the excited state structures. A reliable hybrid B3LYP functional was used in combination with DZ and TZ-quality basis sets. Conclusions. The computed absorption wavelengths are in excellent agreement with the experimental data and are only slightly solvent-dependent. At the same time, the discrepancy with the experiment for Stokes shifts reaches about 20 % at IEF-PCM-TD-B3LYP/6-31G(d). However, the general tendency for both absorption and fluorescence wavelengths is identical for all solvents within one molecule.

The following review article attempts to compare the antioxidant activity of the compounds. For this purpose, density functional theory/Becke three-parameter Lee–Yang–Parr (DFT/B3LYP) methodology was carried out instead of using pharmacological methodologies because of economic benefits and high accuracy. This methodology filtrates the compounds with the lowest antioxidant activity. At first, the Koopmans' theorem was carried out to calculate some descriptors to compare antioxidants. The energy of the highest occupied molecular orbitals (HOMO) was accepted as the best indicator, and then some studies confirmed that the highest occupied molecular orbital/lowest unoccupied molecular orbital (HOMO–LUMO) energy gap is the more precise descriptor. Although it would be better to compare spin density distribution (SDD) on the oxygen of the corresponding radical in the polarizable continuum model (PCM) to evaluate their capability to chain reaction inhibition. Next, it was mentioned that in the multi-target directed ligands (MTDLs), the antioxidant is connected to other moieties in para positions to create better antioxidants or novel hybrid compounds. Indeed, SDD was introduced as a descriptor for MTDL antioxidant effectiveness. Then, the relation between antioxidants and aromaticity was investigated. The more the aromaticity of an antioxidant, the more stable the corresponding radical is. Subsequently, in preferred antioxidant activity, it was defined that the hydrogen atom transfer (HAT) mechanism is more favored in metabolism phase I. It has been seen that the solvent model can change the antioxidant mechanism. Therefore, the solvent model is more important than the chemical structure of antioxidants, and an ideal antioxidant should be evaluated in PCM for pharmacological evaluations. [ABSTRACT FROM AUTHOR]

Natural bond orbital analysis, salvation, and substituent effects of electron-releasing (–CH3, –OH) and electron-withdrawing (–Cl, –NO2, –CF3) groups at para positions on the molecular structure of synthesized 3-phenylbenzo[ d ]thiazole-2(3 H)-imine and its derivatives in selected solvents (acetone, toluene, and ethanol) and in the gas phase by employing the polarizable continuum method model are studied using the M06-2x method and 6-311++G(d,p) basis set. The relative stability of the studied compounds is influenced by the possibility of intramolecular interactions between substituents and the electron donor–acceptor centers of the thiazole ring. Furthermore, atomic charges, electron density, chemical thermodynamics, energetic properties, dipole moments, and nucleus-independent chemical shifts of the studied compounds and their relative stability are considered. The dipole moment values and the highest occupied molecular orbital–lowest unoccupied molecular orbital energy gaps reveal different charge-transfer possibilities within the considered molecules. Finally, natural bond orbital analysis is carried out to picture the charge transfer between the localized bonds and lone pairs. [ABSTRACT FROM AUTHOR]

Modeling the electronic and optical properties of organic semiconductors remains a challenge for theory, despite the remarkable progress achieved in the last three decades. The complexity of these systems, including structural (dis)order and the still debated doping mechanisms, has been engaging theorists with different background. Regardless of the common interest across the various communities active in this field, these efforts have not led so far to a truly interdisciplinary research. In the attempt to move further in this direction, we present our perspective as solid-state theorists for the study of molecular materials in different states of matter, ranging from gas-phase compounds to crystalline samples. Considering exemplary systems belonging to the well-known families of oligo-acenes and -thiophenes, we provide a quantitative description of electronic properties and optical excitations obtained with state-of-the-art first-principles methods such as density-functional theory and many-body perturbation theory. Simulating the systems as gas-phase molecules, clusters, and periodic lattices, we are able to identify short- and long-range effects in their electronic structure. While the latter are usually dominant in organic crystals, the former play an important role, too, especially in the case of donor/accepetor complexes. To mitigate the numerical complexity of fully atomistic calculations on organic crystals, we demonstrate the viability of implicit schemes to evaluate band gaps of molecules embedded in isotropic and even anisotropic environments, in quantitative agreement with experiments. In the context of doped organic semiconductors, we show how the crystalline packing enhances the favorable characteristics of these systems for opto-electronic applications. The counter-intuitive behavior predicted for their electronic and optical properties is deciphered with the aid of a tight-binding model, which represents a connection to the most common approaches to evaluate transport properties in these materials.

Building on recent developments, we compare performance of two distinct protocols, namely SMDmPW1PW91/ 6-311+G(2d,p) and CPCM-OLYP/pcSseg-2, for the computation of 15N chemical shifts of nitrogenated aromatic compounds. The latter shows best overall performance (MAD 5.3 ppm) albeit results in chloroform favors the former. [ABSTRACT FROM AUTHOR]

Due to the rigid structure of 1,3,5-triaza-7-phosphaadamantane (PTA), its 31P chemical shift solely depends on non-covalent interactions in which the molecule is involved. The maximum range of change caused by the most common of these, hydrogen bonding, is only 6 ppm, because the active site is one of the PTA nitrogen atoms. In contrast, when the PTA phosphorus atom is coordinated to a metal, the range of change exceeds 100 ppm. This feature can be used to support or reject specific structural models of organometallic transition metal complexes in solution by comparing the experimental and Density Functional Theory (DFT) calculated values of this 31P chemical shift. This approach has been tested on a variety of the metals of groups 8–12 and molecular structures. General recommendations for appropriate basis sets are reported.

A new charge transfer (CT) complex is formed between the n- and π -donor 1-Benzoylpiperazine (1-BNZP) with π - acceptor p -chloranil (CHL). The CT-interaction is characterized in the defined polar solvent (acetonitile: ACN) at different temperatures. The 1:1 composition of the CT complex is proved. Benesi-Hildebrand method is used to find the stability constant (K CT) and molar extinction coefficient (ε). The more stability of CT complex is suggested from observed results. The thermodynamic parameters (ΔH° and ΔS°) were calculated by using Van't Hoff plot. From these values, CT complex formation process is found to be endothermic and spontaneous. FT-IR study gives information about stretching frequencies of mono substituted product of CT complex. TGA-DTA study is used for thermal stability of product. Morphology study is used to estimate the size and structure of the product. EDX spectrum is used for elemental analysis in the stoichiometric ratio. Theoretical investigation of the CT complex using DFT and TD-DFT also supports the experimental work. The C=O bond length of CHL increases on complexation with 1-BNZP along with significant amount of charge transfer from donor to acceptor. The HOMO-LUMO computation for protonated form of complex suggests a mono substituted product is formed via inner sigma (σ) complex. Image 1 • The CT-complex obtained in purple color between the donor and the acceptor in acetonitrile solvent. • The spectral investigation has been planned in order to achieve various physical parameters of CT-complex. • DFT study has been performed on the donor, acceptor as well as on the CT complex (Gas phase/PCM) at B3LYP level. • Inner sigma (σ) complex of CT-complex has been confirmed by theoretical protonated DFT (PCM) study. [ABSTRACT FROM AUTHOR]

The methods for the experimental determination of electric dipole moment of molecules in solution from measurements of dielectric permittivity and refractive index are traditionally based on the classical Onsager model. In this model the molecular solute is approximated as a simple polarizable point dipole inside a spherical or ellipsoidal cavity of a dielectric medium representing the solvent. However, the inadequacies of the model resulting from the assumption of a simple shape of the cavity, for the evaluation of the cavity field effect, and from the uncertainty of the polarizability of the molecular solute influences the results and hampers the comparison with the electric dipole moments computed from quantum chemical solvation models. In this article we propose a new method for the experimental determination of the electric dipole moment in solution in which information from the Polarizable Continuum Model calculations are used in place of the Onsager model. The new method overcomes the limitations of this latter model regarding both the cavity field effect and the polarizability of the molecular solutes, and thus allows a coherent comparison between experimental and computed dipole moments of solvated molecules. © 2019 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

An implicit account of the solvent effect can be carried out using traditional static quantum chemistry calculations by applying an external electric field to the studied molecular system. This approach allows one to distinguish between the effects of the macroscopic reaction field of the solvent and specific solute–solvent interactions. In this study, we report on the dependence of the simulation results on the use of the polarizable continuum approximation and on the importance of the solvent effect in nonpolar solvents. The latter was demonstrated using experimental data on tautomeric equilibria between the pyridone and hydroxypyridine forms of 2,6-di-tert-butyl-4-hydroxy-pyridine in cyclohexane and chloroform.

The location of a mobile proton in acid-base complexes in aprotic solvents can be predicted using a simplified Adduct under Field (AuF) approach, where solute−solvent effects on the geometry of hydrogen bond are simulated using a fictitious external electric field. The parameters of the field have been estimated using experimental data on acid-base complexes in CDF3/CDClF2. With some limitations, they can be applied to the chemically similar CHCl3 and CH2Cl2. The obtained data indicate that the solute−solvent effects are critically important regardless of the type of complexes. The temperature dependences of the strength and fluctuation rate of the field explain the behavior of experimentally measured parameters.

In this paper, an efficient solver for the polarizable continuum model in quantum chemistry is developed which takes the solvent excluded surface (the smooth molecular surface) as the solute–solvent boundary. This model requires to solve a generalized Poisson (GP) equation defined in ℝ3 with a space-dependent dielectric permittivity function. First, the original GP-equation is transformed into a system of two coupled equations defined in a bounded domain. Then, this domain is decomposed into overlapping balls and the Schwarz domain decomposition method is used. This method involves a direct Laplace solver and an efficient GP-solver to solve the local sub-equations in balls. For each solver, the spherical harmonics are used as basis functions in the angular direction of the spherical coordinate system. A series of numerical experiments are presented to test the performance of this method. [ABSTRACT FROM AUTHOR]

Density functional and MP2 calculations have been carried out on 3,6-anhydro-α- d -galactose, one of the monosaccharides constituting carrageenans. In order to determine the impact of the orientations of the hydroxyl groups on the energy landscape, we generated three isoenergetic maps using B3LYP/6-31G(d) first in the gas phase and then in aqueous medium using two models to simulate the solvent effect; the Onsager and the polarized continuum models. In order to test the effect of the influence of the diffuse function, we decided to produce two others isoenergetic maps using B3LYP/6-31+G(d) level, first in the gas phase and the second in the implicit solvent using the PCM model. The obtained lower energy conformers were then fully optimized using B3LYP, B3PW91 and MP2 with different basis sets. The results are then compared with those reported in previous works using molecular mechanics or dynamics calculations. [ABSTRACT FROM AUTHOR]