Onsager Reaction Field Model Research Articles

Size-Specific ZnO Quantum Dots as Onsager Cavity in Ooshika–Mataga–Lippert Equation

The influence of the surrounding solvent medium to a solute molecule in solution can be treated within the framework of Onsager reaction field model which is based on the assumption that the solute is reduced to a point dipole at the center of a spherical cavity inside the solvent that can be described as the homogeneous, polarizable medium of specific dielectric constant. When the solute molecules are excited in solution of the polar solvent, the changes in the photophysical properties of the solute are manifested through shifts in the maxima of absorption and fluorescence spectra and the observation can be interpreted in terms of the Ooshika–Mataga–Lippert equation. Over several decades, a wide variety of organic molecules as fluoroprobes have been explored to reveal the polarity of their immediate solvent environment. However, while these molecular probes, with diameters less than 10 A, have been employed so far in the literature as Onsager cavities, the limiting value of their radii has not been restr...

Ultrasonic, DFT and FT-IR studies on hydrogen bonding interactions in aqueous solutions of diethylene glycol

The density, viscosity and ultrasonic velocity measurements were carried out in aqueous diethylene glycol (DEG) solutions at different concentrations and temperatures to illustrate the hydrogen bonding interactions of DEG with water. The main acoustic parameters such as isentropic compressibility (βs), acoustic impedance (Z), hydration number (Hn), intermolecular free length (Lf), classical sound absorption (α/f2)class and shear relaxation time (τ) were calculated based on the experimentally measured values. These parameters have been utilized to study the solute–solvent interactions in aqueous DEG solutions. Further, these results suggest that the clusters of likely complex DEG molecule form hydrogen bonding with five water molecules in aqueous solution. The quantum chemical calculations were also performed to study the hydrogen bonding interactions between DEG in g−g+t–tg−t conformation and five water molecules. Computations have been done by DFT method at B3LYP/6-311+g(d,p) level of theory to study the equilibrium structure of DEG monomer in gas phase, DEG–(water)5 interacting complex in gas and solvation phases and the vibrational frequency shift due to formation of intermolecular hydrogen bonding. The solvation phase study was carried out using Onsager's reaction field model in water solvent. The computed and scaled vibrational frequencies are in good agreement with the main features of the experimental spectrum when five water molecules are considered explicitly with DEG in g−g+t–tg−t conformation. The parameters such as optimization energy (Etotal), hydrogen bond length and dipole moment (μm) of the interacting complex are also presented and discussed within the light of solute–solvent interactions.

MOLECULAR STRUCTURE, VIBRATIONAL ASSIGNMENTS, CONFORMATIONAL STABILITY, GROUND AND EXCITED STATE HYDROGEN-BONDING ANALYSIS OF 2-NITROSO VINYL AMINE

In the present work, a detailed conformational study is performed using several computational methods, including density functional theory (DFT) (B3LYP), MP2 and G2MP2 on 2-Nitroso vinyl amine (NVA) in order to determine the stability order of conformers and the various possibilities of intramolecular hydrogen bonding (HB) formation. Four conformers exhibit HB . This feature, although not being the dominant factor in energetic terms, appears to be of foremost importance to define the geometry of the molecule. According to our theoretical results, oximimine conformers are more stable than the corresponding nitrosoamine and nitrosoimine analogues. Theoretical calculations show the following order for intramolecular HB strength in the conformers of title compound: [Formula: see text]The nature of intramolecular HB has been investigated by means of the Bader theory of atoms in molecules (AIM) and natural bond orbital (NBO) analysis. Also, Harmonic Oscillator Model of Aromaticity (HOMA) index as a geometrical indicator of a local aromaticity are investigated. The influence of the solvent on the stability order of conformers and the strength of intramolecular HB is considered using the Onsager reaction field model. The calculated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies confirm that charge transfer occur within the molecule. Further verification of the obtained transition state structures were implemented via intrinsic reaction coordinate (IRC) analysis. Calculations of the1H NMR chemical shift at GIAO/B3LYP/6–311++G** levels of theory are also presented. The excited-state properties of intramolecular HB in H -bonded systems have been investigated theoretically using the time-dependent density functional theory (TD-DFT) method. The complete vibrational assignment for three H -bonded conformers has been made on the basis of the calculated potential energy distribution (PED).

Evaluation of Acidity Constants and Evolution of Electronic Features of Phenol Derivatives in Different Compositions of Methanol/Water Mixture

This work was devoted to evaluation of acidity constants of 28 phenol derivatives in 11 different compositions of methanol/water solvent mixtures. The Onsager reaction field model was applied to any molecule of phenol derivatives dissolved in binary mixture of methanol/water, and the quantum chemical descriptors of the solute were calculated. Multiple linear regression was used to perform the reliable QSPR models in order to predict the acidity constants of the solutes. It was explored that the solvation of phenol derivatives in solvent of binary mixture of methanol/water shows a different behavior as the composition of methanol varies. Four different mechanisms proposed for solvation in 0–100 volume percent of methanol solvent. It was seen that the dipole‐dipole interactions increase as the amount of methanol increases in solvent mixture, which implies the contribution of highly negative oxygens of methanol on hydrogen bondings between solute and solvent cavity. The orbital energies are a major electronic descriptor on solvation processes. This proposes that the charge exchange between frontier orbital energies of anions and the solvent molecules is the major event occurring in solution in order to stabilize the produced anions.

Theoretical and experimental studies on solubility and reactivity behavior of lysergol, elymoclavine, and dihydrolysergol

Lysergol, elymoclavine (Δ9,10 and Δ8,9 regioisomers), and dihydrolysergol are important members of ergolines. The present work reports their comparative study in gas and solvent phase (water) that has been performed both experimentally and theoretically. Theortical calculations have been carried within the density functional theory formalism to analyze the structural and electronic properties of these molecules with B3LYP hybrid exchange–correlational fuctional in conjunction with 6-311++G (d,p) basis set. Hessian calculations are performed at B3LYP/6-31G (d,p) level of theory in gas phase as well as other solvent phases. Solvent phase calculations are performed using Onsager reaction field model as implemented in Gaussian 03. A good agreement has been found between experimental and theoretical infrared and nuclear magnetic resonance (NMR) spectra. The calculated NMR data has been analyzed statistically. Stability of these regioisomers has been analyzed in terms of the energy gap between highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO–LUMO gap). Calculations for lysergol and elymoclavine in water as solvent were carried to examine the effect of solvent on the HOMO–LUMO levels and energy of these molecules. © 2012 Wiley Periodicals, Inc.

Effective Solvent Cavity for 1-Hydroxy-9,10-anthraquinone Derivatives in Methanol/Water, Using a Local QSAR Study Method

The Onsager reaction field model was applied to 1-hydroxy-9,10-anthraquinone derivatives dissolved in binary solvent mixtures of methanol/water. Each solution was placed in a cavity surrounded by a continuous dielectric constant medium, and then the quantum chemical descriptors of the solute were calculated. Multiple linear regression was used to perform the QSPR model calculations in order to predict the acidity constants of the solutes. The resultant hexa-parametric model was able to predict the acidity constants within absolute average deviations less than 1.82 %. The proposed model suggests that the acidic property of the solute is controlled by solvation processes through coulombic interactions as well as orbital energies. It was found that the solvent lowered the excited orbital energy states of all 1-hydroxy-9,10-anthraquinone derivatives. The model proposes that an effective solvation cavity needs more methanol molecules than water in order to increase the solvation energy in the solution.

Negative solvatochromism of a series of pyridinium phenolate betaine dyes with increasing steric hindrance

The negative solvatochromism of a series of pyridinium phenolates betaine dyes is investigated using three approaches: (a) empirical, based on the empirical solvent polarity parameter ET(30); (b) semi-empirical, based on the π∗, α, β set of parameters used in Kamlet–Taft’s Solvatochromic Comparison Method (SCM); and (c) physical, by means of the Onsager reaction-field model of solvents. Comparison of the obtained correlations underscored the roles of both the two tert-butyl groups ortho to the oxygen atom and the interplanar angle between the phenyl rings on the very blue shifts observed as the polarity increases.

Evaluation of Acidity Constants of Anthraquinone Derivatives in Methanol/Water Mixtures Using Real Quantum Descriptors

This work presents an evaluation of the acidity constants of 1-hydroxy-9,10-anthraquinone derivatives using electronic descriptors in four methanol/water mixtures with different volume percents and in isolation. An Onsager reaction field model was applied for charges, orbital energies, and dipole descriptors of solutes in the four different solvent mixtures with different volume percents. Each solute was placed in a cavity surrounded by a continuous dielectric constant medium, and the quantum chemical descriptors of the solute were calculated. Electrostatic potential energy descriptors of the isolated solutes were obtained using density functional theory. Relevant descriptors affecting the acidities of the anthraquinones were selected using a genetic algorithm (GA) method. Contributions of the selected variables to the prediction of the experimental acidity constant values were determined by applying a multi-layer perceptron-based feedforward artificial neural network (ANN). A proper model, reproducing experimental acidity constants within average absolute errors of less than 1.10% was achieved. The model proposed relatively higher contributions of dipoles (insolvent) and electrostatic potentials (in isolation) than the orbital energies, revealing the role of strong dipole–dipole interactions such as hydrogen bonds as well as halogen bonds in the proton dissociation process. The gaps between the HOMO and LUMO energies were found to contribute to the stabilization of anions leading to higher dissociation constants.

DFT/TDDFT study on the electronic structure and spectral properties in annulated analogue of phenyl heteroazulene derivative

Paper reports the DFT/TDDFT study on the electronic structure and spectral properties of the seven-membered annulated heteroazulene derivative 6-phenyl-6H-5,6,7-triazadibenzo[f,h]naphtho[3,2,1-cd]azulene (PTNA) by means of polarizable continuum model (PCM) and Lippert–Mataga–Onsager reaction field (LM-ORF) model at the B3LYP/6-31+G(d,p) level of theory. The results of calculations are compared with the measured optical absorption and fluorescence spectra as well as with the cyclic voltammetry data. The DFT/TDDFT methods exhibit rather good quantitative agreement regarding the spectral position of the first absorption band; the discrepancy between the experiment and theory is less than 0.1eV. As for the fluorescence emission the TDDFT calculations underestimate the transition energy of about 0.45eV. The discrepancy should be attributed to insufficient accuracy of the TDDFT optimization in the excited state. In the polar solvent environment, all the TDDFT/PCM approaches give the bathochromic (red) shift for the fluorescence emission and the hypsochromic (blue) shift for the optical absorption in accordance with the experimental observation. As for the fluorescence emission fairly good agreement with the experiment provides the hybrid approach being the combination of the TDDFT/PCM optimization with the semiempirical electronic structure calculations by PM3 method and solvation LM-ORF model predicting the emission energy in different solvents with the accuracy better than 0.06eV.

Computational Study of Promising Organic Dyes for High-Performance Sensitized Solar Cells

The energy transition from the ground state to the first excited singlet of four organic dye candidates to be used as sensitizers in solar cells, D5, D7, D9, and D11, has been computationally explored and compared to experimental results with TDDFT (B3LYP, ωB97, and ωB97X functionals) and the CIS(D) and SOS-CIS(D) wave function based methods. The second-order perturbation correction to CI singles’ excitation energies are superior to any TDDFT functional employed here. The performance of SOS-CIS(D) is especially interesting, being in good agreement with absorption spectra and having important computational savings. The best TDDFT results are obtained by the ωB97X functional. Solvation effects on the excitation energies have been studied with three different models, i.e., the Onsager reaction field model, SS(V)PE, and SM8.

Study of vibrational relaxation and molecular reorientation in liquids: a Raman spectroscopic study

AbstractThe vibrational relaxation and molecular reorientational processes in liquids have been studied in some carbonyl‐containing molecules using the acetonitrile (ACN) solvent. The vibrational and reorientational processes have been studied in correspondence with correlation times. The screening effect due to dielectric has been studied and the Onsager reaction field model has been tested. The study shows that repulsive types of intermolecular forces play an important role in complex systems. Copyright © 2010 John Wiley & Sons, Ltd.

Ultrasonic and DFT study of intermolecular association through hydrogen bonding in aqueous solutions of d(−)-arabinose

The experimental measurements of density, viscosity and ultrasonic velocity of aqueous d-arabinose solutions were carried out as functions of concentration (0.1 ≤ m [mol kg − 1 ] ≤ 1.0) and temperature (303.15 ≤ T [K] ≤ 323.15). The isentropic compressibility ( β s), acoustic impedance ( Z), hydration number ( H n), intermolecular free length ( L f), classical sound absorption ( α/ f 2) class and shear relaxation time ( τ) were calculated by using the measured data. These parameters have been interpreted in terms of solute–solvent interactions. The quantum chemical calculations were performed to study the hydrogen bonding in interacting complex formed between α-D-arabinopyranose in 1C 4 conformation and water molecules. Computations have been done by using Density Functional Theory (DFT) method at B3LYP/6-31+g(d) level of theory to study the equilibrium structure of α- d-arabinose, α-D-arabinopyranose–water interacting complex and vibrational frequencies. The solution phase study was carried out using Onsager's reaction field model in water solvent. The computed and scaled vibrational frequencies are in good agreement with the main features of the experimental spectrum when seven water molecules are considered explicitly with α-D-arabinopyranose in 1C 4 conformation. The interaction energy ( E total), hydrogen bond lengths and dipole moment ( μ m) of the interacting complex are also presented and discussed with in the light of solute–solvent interactions.

Conformation and vibrational spectra and assignment of 2-thenoyltrifluoroacetone

The conformational stabilities of different tautomers of 2-thenoyltrifluoroacetone (4,4,4-trifluoro-1-(2-thienyl)butane-1,3-dione, TTFA) in several solutions have been investigated at the B3LYP level using 6-311++G** basis set. The self-consistent Onsager reaction field model was used to study the solvent effects. It was determined that the energy differences of the most stable conformers (stabilized by the hydrogen bridge), which are negligible in the gas phase, increase in the solvent media. The harmonic vibrational frequencies were calculated at the B3LYP level using 6-31G** and 6-311G** basis sets. A complete vibrational assignment has been clearly provided for the experimental IR and Raman spectra of TTFA and its deuterated analogue, which shows coexisting of four conformations in the sample. This vibrational spectroscopy analyses confirms more content of the “A” forms in the solution than the “B” forms, although the reverse is true in the solid state, in agreement with the theoretical DFT calculations and the experimental X-ray results.

Theoretical modeling and experimental studies on N-n-Decyl-2-oxo-5-nitro-1-benzylidene-methylamine

The Schiff base compound, N-n-Decyl-2-oxo-5-nitro-1-benzylidene-methylamine, has been -synthesized and characterized by IR, electronic spectroscopy, and X-ray single-crystal determination. Molecular geometry from X-ray experiment of the title compound in the ground state have been compared using the Hartree-Fock (HF) and density functional method (B3LYP) with 6-31G(d) basis set. Calculated results show that density functional theory (DFT) at B3LYP/6-31G(d) level can well reproduce the structure of the title compound. To investigate the solvent effect for the atomic charge distributions of the title compound, self-consistent reaction field theory with Onsager reaction field model was used. In addition, DFT calculations of the title compound, molecular electrostatic potential and thermodynamic properties were performed at B3LYP/6-31G(d) level of theory.

1H NMR spectrum and computational study of firefly luciferin in dimethyl sulfoxide

Experimental and theoretical 1H NMR chemical shift values ( δs) of firefly luciferin (Ln) in dimethyl sulfoxide (DMSO) were studied for the estimation of the detailed structure of Ln and the characteristics of the interaction between Ln and DMSO. The 1H chemical shifts were recorded in DMSO- d 6. The temperature dependence of δ obs.s of Ln of the 1H NMR chemical shifts was also measured. The theoretical NMR chemical shifts ( δ calc.s) were calculated based on the GIAO DFT approach, using the 6-311+G(2d,p) basis set (a total of 544 contracted basis functions), implemented in the Gaussian software package. The solvent effect was obtained by means of the Onsager reaction field model or an Ln···DMSO hydrogen-bonded complex model. The calculated results of the Ln···DMSO complex model are in good agreement with the observed chemical shifts, but all observed 1H peaks could not be reproduced for the optimized structure of Ln using the Onsager reaction field model. The considerably large δ obs.s of –H and –OOH protons of Ln in the observed 1H NMR spectra are probably explained in terms of hydrogen-bonded complex model between protons in Ln and oxygen atoms in DMSO molecules, rather than in the Onsager reaction field model.

Ultrasonic and DFT study of intermolecular association through hydrogen bonding in aqueous solutions of glycerol

The experimental measurements of density, viscosity and ultrasonic velocity of aqueous glycerol solutions were carried out as functions of concentration (0.1 ≤ m [mol kg − 1 ] ≤ 1.0) and temperature (303.15 ≤ T [K] ≤323.15). The isentropic compressibility ( β s ), acoustic impedance ( Z), hydration number ( H n), intermolecular free length ( L f), classical sound absorption ( α/ f 2) class and shear relaxation time ( τ) were calculated by using the measured data. These parameters have been interpreted in terms of solute–solvent interactions. The quantum chemical calculations were performed to study the hydrogen bonding in interacting complex formed between glycerol and water molecules. Computations have been done by using Density Functional Theory (DFT) method at B3LYP/6–31 + g(d) level of theory to study the equilibrium structure of glycerol, glycerol–water interacting complex and vibrational frequencies. The solution phase study was carried out using Onsager's reaction field model in water solvent. The computed vibrational frequencies are in good agreement with the main features of the experimental spectrum when four water molecules are considered explicitly with glycerol. The interaction energy ( E total), hydrogen bond lengths and dipole moment ( µ m) of the interacting complex are also presented and discussed with in the light of solute–solvent interactions.

Solvent effects on structure and optical properties of a D-π-A azobenzene dye

Time-dependent hybrid density functional theory in combination with Onsager reaction field model and super-molecular model has been applied to study solvent effects on the geometrical and electronic structures, as well as one/two-photon absorption properties, of 4-(N-(2-hydroxyethyl)-N-methyl)-amino-4'-nitroazobenzene. It is found that the short-range interaction has a large effect on the electronic structure of the solute molecule, namely, large red-shift of the maximum one-photon absorption is induced by hydrogen bonding. The solute molecule has a large two-photon absorption cross section, which is enhanced by the solvent effect. The computational results are in good agreement with measurements.

STRUCTURE AND VIBRATIONAL FREQUENCIES OF Ph3PCl2 WITH DISCRETE SOLVENT MOLECULES AND IN GAS PHASE

Triphenyldichlorophosphorane ( Ph 3 PCl 2) in solution was studied with cluster model of discrete water molecules and the Onsager reaction field model. The geometry of Ph 3 PCl 2– H 2 O cluster is optimized with DFT-PW91 and DZVP basis sets. A weak hydrogen bond is formed between Cl and H atom of the water molecule. The geometry data of Ph 3 PCl 2 molecule is altered due to the presence of water molecule. The bond length of P – Cl 2 increases from 2.501 Å to 2.832 Å, and the P – Cl 1 bond length decreases from 2.113 Å to 2.064 Å. Three C – P bonds have slightly changed. The geometrical parameters of the three benzene rings do not change much upon clustering. To compare with solution structure, gas structure of Ph 3 PCl 2 also was investigated. Four stationary structures were found. The trigonal bipyramidal structure C is a penta-coordinated structure and the most stable one. This is in agreement with the previous research. The trigonal bipyramidal structure C and the ionic structure A has no imaginary frequency. The structure B and structure D have an imaginary frequency of -41.9 cm-1 and -7.4 cm-1, respectively.

Excited State Intramolecular Proton Transfer in 2-(2‘-Arylsulfonamidophenyl)benzimidazole Derivatives: Insights into the Origin of Donor Substituent-Induced Emission Energy Shifts

Donor-substituted 2-(2'-arylsulfonamidophenyl)benzimidazoles undergo efficient excited-state intramolecular proton transfer (ESIPT) upon photoexcitation. The tautomer emission energy depends strongly on the substituent attachment position on the fluorophore pi-system. While substitution with a donor group in the para-position relative to the sulfonamide moiety yields an emission energy that is red-shifted relative to the unsubstituted fluorophore, fluorescence of the meta-substituted derivative appears blue-shifted. To elucidate the origin of the surprisingly divergent emission shifts, we performed detailed photophysical and quantum chemical studies with a series of methoxy- and pyrrole-substituted derivatives. The nature and contribution of solvent-solute interactions on the emission properties were analyzed on the basis of solvatochromic shift data using Onsager's reaction field model, Reichardt's empirical solvent polarity scale ET(30), as well as Kamlet-Abboud-Taft's empirical solvent index. The studies revealed that all ESIPT tautomers emit from a moderately polarized excited-state whose dipole moment is not strongly influenced by the donor-attachment position. Furthermore, the negative solvatochromic shift behavior was most pronounced in protic solvents presumably due to specific hydrogen-bonding interactions. The extrapolated gas-phase emission energies correlated qualitatively well with the trends in Stokes shifts, suggesting that solute-solvent interactions do not play a significant role in explaining the divergent emission energy shifts. Detailed quantum chemical calculations not only confirmed the moderately polarized nature of the ESIPT tautomers but also provided a rational for the observed emission shifts based on the differential change in the HOMO and LUMO energies. The results gained from this study should provide guidelines for tuning the emission properties of this class of ESIPT fluorophores with potential applications in analytical chemistry, biochemistry, or materials science.

Ultrasonic and computational study of intermolecular association through hydrogen bonding in aqueous solutions of d-mannitol

The estimation of density, viscosity and ultrasonic velocity of aqueous d-mannitol solutions was carried out as functions of concentration (0.1 ≤ m [mol kg − 1 ] ≤ 1.0) and temperature (303.15 ≤ T [K] ≤ 323.15). The adiabatic compressibility ( β ad), hydration number ( H n), internal pressure ( π i), classical sound absorption ( α/ f 2) class and shear relaxation time ( τ) were calculated through ultrasonic experimental method. These parameters have been interpreted in terms of solute–solvent interactions. The quantum chemical calculations were performed to study the hydrogen bonding in interacting complex formed between mannitol and water molecules. Computations have been done by using Density Functional Theory (DFT) method at B3LYP/6–31 + g( d) level of theory to study the equilibrium structure of mannitol, mannitol–water interacting complex and vibrational frequencies. The solution phase study was carried out using Onsager's reaction field model in water solvent. The computed vibrational frequencies are in good agreement with the main features of the experimental spectrum when eight water molecules are considered explicitly with the d-mannitol. The interaction energy ( E total), hydrogen bond lengths and dipole moment ( μ m) of the interacting complex were also presented and discussed within the light of solute–solvent interactions.