Conductor Polarizable Continuum Model Research Articles

Assessing Implicit and Explicit Polarizable Solvation Models for Nuclear-Electronic Orbital Systems: Quantum Proton Polarization and Solvation Energetics.

Accurate simulations of many chemical processes require the inclusion of both nuclear quantum effects and a solvent environment. The nuclear-electronic orbital (NEO) approach, which treats electrons and select nuclei quantum mechanically on the same level, combined with a polarizable continuum model (PCM) for the solvent environment, addresses this challenge in a computationally practical manner. In this work, the NEO-PCM approach is extended beyond the IEF-PCM (integral equation formalism PCM) and C-PCM (conductor PCM) approaches to the SS(V)PE (surface and simulation of volume polarization for electrostatics) and ddCOSMO (domain decomposed conductor-like screening model) approaches. IEF-PCM, SS(V)PE, C-PCM, and ddCOSMO all exhibit similar solvation energies as well as comparable nuclear polarization within the NEO framework. The calculations show that the nuclear density does not leak out of the molecular cavity because it is much more localized than the electronic density. Finally, the polarization of quantized protons is analyzed in both continuum solvent and explicit solvent environments described by the polarizable MB-pol model, illustrating the impact of specific hydrogen-bonding interactions captured only by explicit solvation. These calculations highlight the relationship among solvation formalism, nuclear polarization, and energetics.

DFT/TD-DFT investigation on the photoinduced electron transfer of diruthenium and viologen complexes

Photoinduced electron transfer, chemical stability, and redox property of diruthenium−viologen complexes were investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. Target systems include a series of diruthenium and viologen complexes consisting of Ru(bpy)3-viologen-Ru(bpy)3; Ru–V–Ru, Ru(bpy)3-viologen-Ru(bpy)(dcbpy)2; Ru–V–RuCOOH, and Ru(bpy)3-viologen-viologen-Ru(bpy)3; Ru–V–V–Ru, where bpy = 2,2′-bipyridyl and dcbpy = 4,4′-dicarboxyl-2,2-bipyridyl. The B3LYP functional was used to investigate the ground state properties for the three diruthenium and viologen complexes and for two parent complexes: ruthenium-bipyridine (Ru(bpy)32+) and methyl viologen (MV2+) as well as their oxidized states. Singlet excited states were examined using the TD-DFT calculations with CAM-B3LYP functional in acetonitrile using conductor polarizable continuum model (CPCM). The TD-DFT calculations reproduced the experimentally observed variation of the absorption spectra due to oxidation states. The correlation between the calculated UV–Vis transition and molecular orbitals for the excited state clearly established that the viologen dication (V2+) changed their reductive product into the radical cation (V•+) and neutral (V0), whereas ruthenium retained its formal Ru(bpy)32+ oxidation state. The metal to ligand charge transfer state of Ru(bpy)32+ was shown to undergo electron transfer quenching by methyl viologen dication (MV2+). These findings are relevant for the development of novel optoelectronic materials owing to a combination of chemical stability, redox activity, and long-lived excited states.

PROTON TRANSFER IN PHOSPHORUS-CONTAINING ACID–N,N-DIMETHYLFORMAMIDE SYSTEM WITH GLANCE OF ENVIRONMENT

Proton transfer processes in the molecular and ion-molecular complexes of phosphorus acids (phosphoric H3PO4, phosphorous H3PO3, methylphosphonic СН3Н2РО3) with N,N-dimethylformamide (DMF) was studied. The potential energy surface (PES) for proton transfer was studied using the B3LYP/6-31++G(d,p) level of theory, and the solvent effect (here DMF) on the PES was included using the conductor polarized continuum model (CPCM). For all cases, the energy profile for proton transfer represents a double well curve, if intermolecular O…Odistance for the hydrogen bond considered has a fixed length equal to 2.7 Å. The solvent effect favors a proton transfer in the molecular complexes, but no shift of the equilibrium towards ionic pairs is observed. As a result, the energy values associated with proton transfer are significantly reduced in comparison with those found for the gas phase. The proton transfer in the complexes of H3PO4 with DMF is more favored than this process for the cases with H3PO3 and СН3Н2РО3. The probability of proton transfer in the Н3РО4–DMF and (Н3РО4)2–DMF is nearly identical. On the contrary, the barrier height for transfer in Н3РО4–(DMF)n for n=1÷3 increases with increasing number of DMF molecules. The energy barrier for proton transfer in the DMFH+–DMF and H3PO4–H2PO4– is lower than the ones for the molecular complexes.

THE INVESTIGATION OF SPECTROSCOPIC AND THEORETICAL METHODS OF BISISOXAOLINE DERIVATIVE OF NORBORNADIEN

In this study, the synthesis of bisisoxaoline derivative of norbornadien from heterocyclic compounds was performed via 1,3-dipolar cycloaddition reaction, the structural properties of derivative characterized by spectroscopic analysis such as FT-IR, 1 H-NMR, 13 C-NMR, UV-Vis and the single-crystal X-ray diffraction technique. The 3,7-bis(4-(tert-butyl)phenyl)-3a,4,4a,7a,8,8a-hexahydro-4,8-methanobenzo[1,2-d:4,5-d’]diisoxazole compound was optimized using Density Functional Theory (DFT/B3LYP) method with 6-311G(d,p) basis set in the ground state and the geometric parameters compared with single-crystal X-ray diffraction technique. The compound crystallizes in the monoclinic space group C2/c with a = 20.634(4) Å, b = 11.179(2) Å, c = 11.0690(17) Å and Z = 4 unit cell parameters. Also, the spectral results were examined with calculated vibrational frequencies, 1 H-NMR, 13 C-NMR chemical shift values and absorption wavelengths, theoretically. The energetic behaviour of the compound in different solvent media was examined with TD-DFT/B3LYP method and 6-311G(d,p) basis set using the Conductor Polarizable Continuum Model (CPCM). The frontier molecular orbitals (FMOs), molecular electrostatic potential (MEP) and electronic structure parameters (dipole moment, electronegativity, chemical hardness-softness, ionization potential, electron affinity, etc.) were examined to get information about the chemical stability of the structure.

Proton transfer in the molecular complexes of phosphorus acids with DMSO

Proton transfer processes in various H-bonded complexes of phosphoric (H3PO4), phosphorous (H3PO3) and methylphosphonic (H2MePO3) acids with dimethyl sulfoxide (DMSO), i.e., (acid)2–DMSO, acid–(DMSO) n for n = 1, 2 and H3PO4–(DMSO)3 have been studied. The potential energy surface (PES) for proton transfer was investigated using the B3LYP level of theory, and the solvent effect on the PES was included using the conductor polarized continuum model. The energy curves for proton transfer from acid to DMSO oxygen atom in all investigated complexes represent single-well potentials, if no constraints are imposed on the system. The PES obtained by optimizing the geometry of each complex at fixed O···O distances has two nonsymmetric minima with respect to the energy barrier. In these cases, the distance at which a barrier starts to rise is slightly different. The energy barrier for proton transfer in all considered complexes increases in the series of acids: H3PO4 < H3PO3 < H2MePO3. The energies associated with proton transfer in the complexes of all investigated acid with DMSO become higher with increasing number of DMSO molecules. For all complexes, the effect of DMSO environment favors a proton transfer.

Theoretical Investigation of the Effect of (8,0) Single-walled Carbon Nanotubes on Acidity of Aliphatic Alcohols

ONIOM calculation is carried out to estimate the acidity of five aliphatic alcohols before and after adsorbing on the tip of (8,0) single-walled carbon nanotube. The ONIOM method is performed using a combination of density functional theory and AM1 semiemperical method for alcohols and their corresponding conjugated bases. Deprotonation Gibbs free energies of alcohols are calculated and compared before and after adsorbing on the nanotube. Solute-solvent interactions are taken into account by employing the conductor polarized continuum model (CPCM). The results show that the acidity of alcohols change after adsorbing on the nanotubes and these alcohols have a little effect on (8,0) SWCNT.

Prediction of the pKa's of aqueous metal ion +2 complexes.

Aqueous metal ions play an important role in many areas of chemistry. The acidities of [Be(H2O)4](2+), [M(H2O)6](2+), M = Mg(2+), Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), and Hg(2+), and [M(H2O)n](2+), M = Ca(2+) and Sr(2+), n = 7 and 8, complexes have been predicted using density functional theory, second-order Møller-Plesset perturbation theory (MP2), and coupled cluster CCSD(T) theory in the gas phase. pKa's in aqueous solution were predicted by using self-consistent reaction field (SCRF) calculations with different solvation models. The most common binding motif of the majority of the metal +2 complexes is coordination number (CN) 6, with each hexaaquo cluster having reasonably high symmetry for the best arrangement of the water molecules in the first solvation shell. Be(2+) is tetracoordinated, but a second solvation shell of 8 waters is needed to predict the pKa. The Ca(2+) and Sr(2+) aquo clusters have a coordination number of 7 or 8 as found in terms of the energy of the reaction M(H2O)7(2+) + H2O → M(H2O)8(2+) and the pKa values. The calculated geometries are in reasonable agreement with experiment. The SCRF calculations with the conductor-like screening model (COSMO), and the conductor polarized continuum model (CPCM) using COSMO-RS radii, consistently agree best with experiment at the MP2/aug-cc-pVDZ and CCSD(T)/aug-cc-pVDZ levels of theory. The CCSD(T) level provides the most accurate pKa's, and the MP2 level also provides reliable predictions. Our predictions were used to elucidate the properties of metal +2 ion complexes. The pKa predictions provide confirmation of the size of the first solvation shell sizes. The calculations show that it is still difficult to predict pKa's using this cluster/implicit solvent approach to better than 1 pKa unit.

A Hybrid statistical mechanics—quantum chemical model for proton transfer in 5‐azauracil and 6‐azauracil in water solution

A hybrid statistical physics—quantum‐chemical methodology was implemented to study the water‐assisted intramolecular proton‐transfer processes in 5‐ and 6‐azauracils in aqueous solutions. The solvent effects were included in the model by explicit inclusion of two pairs of water molecules, which model the relevant part of the first hydration shell around the solute. The position of these water molecules was initially estimated by carrying out a classical Metropolis of dilute water solutions of the title compounds and subsequently analyzing solute–solvent intermolecular interactions in the Monte Carlo‐generated configurations. Sequentially to the statistical physics simulation, ab initio quantum mechanical (QM) level of theory was implemented. The effects of the water as solvent (at ab initio QM level) were introduced at two different levels—using solute–solvent clusters (four‐water molecules) and using the same clusters embedded in an external continuum. Full geometry optimizations of these complexes were carried out at MP2/6–31 + G(d, p) and conductor‐polarizable continuum model (C‐PCM)/MP2/6–31 + G(d, p). Single point calculations were performed at CCSD(T)/6–31 + G(d, p)//MP2/6–31 + G(d, p) computational level to obtain more accurate energies. According to our calculations hydrated azauracils should exist in three forms: mainly dioxo form and two hydroxy forms. The calculated proton transfer activation energies for tautomeric reactions of 5‐azauracil and 6‐azauracil show different pictures for these two compounds. According to C‐PCM/MP2/6–31 +G(d, p) data, water‐assisted proton transfer in 5‐azauracil realizes through two parallel reactions: 1,3,5‐triazine‐2,4(1H,3H)‐dione → 6‐hydroxy‐1,3,5‐triazin‐2(1H)‐one and 1,3,5‐triazine‐2,4(1H,3H)‐dione → 4‐hydroxy‐1,3,5‐triazin‐2(1H)‐one. Tautomeric equilibrium in 6‐azauracil in water could occur by two contiguous reactions: 1,2,4‐triazine‐3,5(2H,4H)‐dione → 5‐hydroxy‐1,2,4‐triazin‐3(2H)‐one and 5‐hydroxy‐1,2,4‐triazin‐3(2H)‐one → 3‐hydroxy‐1,2,4‐triazin‐5(2H)‐one. The proton transfer investigated reactions in 5‐ and 6‐azauracils involve concerted atomic movement. © 2015 Wiley Periodicals, Inc.

Solvent-induced frequency shifts of 5-hydroxymethylfurfural deduced via infrared spectroscopy and ab initio calculations.

Solvent-induced frequency shifts (SIFS) of the carbonyl stretching vibration ν(C═O) of 5-hydroxymethylfurfural were measured in protic, polar aprotic, and nonpolar solvents. The Gutmann acceptor number (AN) was found to correlate with the measured frequency shifts. The SIFS in six solvents were investigated using ab initio electronic structure calculations, treating the solvent implicitly and with an explicit solvent ligand interacting with the carbonyl. The conductor-polarizable continuum model (CPCM) of solvation predicted that ν(C═O) shifted according with the dielectric constant as (ε - 1)/(2ε + 1), in agreement with the analytical predictions of the Kirkwood-Bauer-Magat (KBM) theory for a dipole in a dielectric continuum, but in disagreement with the experimental trend. The experimental SIFS were best predicted using gas-phase complexes of HMF and explicit solvent-ligand. Natural bond orbital (NBO) analysis and Bader's atoms in molecules theory were used to investigate the electronic structure of these complexes. Strong SIFS were found to arise from stronger H-bonding interactions, as observed in delocalization of carbonyl lone-pair electrons by H-bonding solvent σ*(X-H) orbitals, and an increase in charge density and a decrease in local potential energy at the H-bond (3, -1) critical point. Consequently, by predicting the experimental SIFS and examining the electronic structure, we find the first theoretical evidence for treating Gutmann's solvent AN as a measure of solvent Lewis acidity.

Phenothiazine-azaBODIPY-fullerene supramolecules: syntheses, structural characterization, and photochemical studies.

Photoactive supramolecules composed of two entities of carbamoyl phenothiazines (PTZ) positioned at different locations of the BF2-chelated azadipyrromethene (azaBODIPY) periphery and fulleropyrrolidine (C60) have been newly designed and synthesized to probe excited state events. The X-ray structure of one of the precursor compounds, (PTZ)2-azaBODIPY, revealed spatially well separated PTZ entities without causing any steric hindrance. The supramolecules were fully characterized by spectral, computational, electrochemical and photochemical techniques. The geometry and electronic structures were arrived at by B3LYP/6-31G(dp) calculations (for H, B, N, and O) and B3LYP/6-31G(df) calculations (for S) in benzonitrile utilizing the Conductor Polarizable Continuum Model (CPCM). The different redox states were established from the differential pulse voltammetry (DPV) studies and the data were used to estimate free-energy change associated with the charge separation process. Interestingly, although phenothiazine is known to be a very good electron donor in photosynthetic model compounds and solar energy harvesting dyes, in the present system, the difficulty in oxidizing carbamoyl phenothiazine entities' contribution to the photochemistry originating from the singlet excited azaBODIPY was minimal. Consequently, femtosecond laser flash photolysis studies provided evidence for the occurrence of photoinduced electron transfer from (1)azaBODIPY* to C60 without participation of the PTZ entities. The energy level diagram constructed using spectral and electrochemical data provided a rational explanation for this observation. By monitoring the rise and decay of the fullerene radical ion peak, the measured rate of charge separation, kCS, and charge recombination, kCR, for supramolecule 1 were found to be 3.08 × 10(10) s(-1) and 7.96 × 10(9) s(-1), respectively, while these values for supramolecule 2 were found to be 4.68 × 10(11) s(-1) and 1.13 × 10(10) s(-1), respectively, revealing the occurrence of ultrafast electron transfer events. The photochemically generated (PTZ)2-azaBODIPY˙(+)-C60˙(-) radical ion pair followed a charge recombination path by populating (3)azaBODIPY* prior to returning to the ground state as confirmed by nanosecond transient absorption measurements.

Structure and properties of the precursor/successor complex and transition state of the CrCl²⁺/Cr²⁺ electron self-exchange reaction via the inner-sphere pathway.

The electron self-exchange reaction CrCl(OH2)5(2+) + Cr(OH2)6(2+) → Cr(OH2)6(2+) + CrCl(OH2)5(2+), proceeding via the inner-sphere pathway, was investigated with quantum-chemical methods. Geometry and vibrational frequencies of the precursor/successor (P/S) complex, (H2O)5Cr(III)ClCr(II)(OH2)5(4+)/(H2O)5Cr(II)ClCr(III)(OH2)5(4+), and the transition state (TS), (H2O)5CrClCr(OH2)5(4+‡), were computed with density functional theory (DFT) and conductor polarizable continuum model hydration. Consistent data were obtained solely with long-range-corrected functionals, whereby in this study, LC-BOP was used. Bent and linear structures were computed for the TS and P/S. The electronic coupling matrix element (H(ab)) and the reorganizational energy (λ) were calculated with multistate extended general multiconfiguration quasi-degenerate second-order perturbation theory. The nuclear tunneling factor (Γ(n)), the nuclear frequency factor (ν(n)), the electronic frequency factor (ν(el)), the electron transmission coefficient (κ(el)), and the first-order rate constant (k(et)) for the electron-transfer step (the conversion of the precursor complex into the successor complex) were calculated based on the imaginary frequency (ν(‡)) of the TS, the Gibbs activation energy (ΔG(‡)), H(ab), and λ. The formation of the precursor complex via water substitution at Cr(OH2)6(2+) was also investigated with DFT and found to be very fast. Thus, the electron-transfer step is rate-determining. For the substitution reaction, only a bent TS structure could be obtained. The overall rate constant (k) was estimated as the product K(A)k(et), whereby K(A) is the equilibrium constant for the formation of the ion aggregate of the reactants Cr(OH2)6(2+) and CrCl(OH2)5(2+), Cr(H2O)6·CrCl(OH2)5(4+) (IAR). k calculated for the bent and linear isomers agrees with the experimental value.

Origin of anomalous electronic circular dichroism spectrum of RuPt2(tppz)2Cl2(PF6)4 in acetonitrile.

We report a theoretical study of the structures, energetics, and electronic spectra of the Pt(II)/Ru(II) mixed-metal complex RuPt2(tppz)2Cl2(PF6)4 (tppz = 2,3,5,6-tetra(2-pyridyl)pyrazine) in acetonitrile. The hybrid B3LYP density functional theory and its TDDFT methods were used with a complete basis set (CBS) extrapolation scheme and a conductor polarizable continuum model (C-PCM) for solvation effects. Results showed that the trinuclear complex has four types of stable conformers and/or enantiomers. They are separated by high barriers owing to the repulsive H/H geometrical constraints in tppz. A strong entropy effect was found for the dissociation of RuPt2(tppz)2Cl2(PF6)n in acetonitrile. The UV-visible and emission spectra of the complex were also simulated. They are in good agreement with experiments. In this work we have largely focused on exploring the origin of anomalous electronic circular dichroism (ECD) spectra of the RuPt2(tppz)2Cl2(PF6)4 complex in acetonitrile. As a result, a new mechanism has been proposed together with a clear illustration by using a physical model.

Quantum chemical and spectroscopic (FT-IR and FT-Raman) investigations of 3-methyl-3h-imidazole-4-carbaldehyde

FT-IR and FT-Raman spectra of 3-methyl-3h-imidazole-4-carbaldehyde (3M3HI4C) were recorded in the region 4000–400cm−1 and 3500–50cm−1, respectively. Optimized geometric parameters, conformational equilibria, normal mode frequencies, and corresponding vibrational assignments of 3M3HI4C were theoretically examined by quantum chemical methods for the first time. All vibrational frequencies were assigned in detail with the help of total energy distribution (TEDs). The experimental wavenumbers were compared with the scaled vibrational frequencies determined by DFT/B3LYP method. The results showed that the B3LYP/6-311++G(d,p) method predicts vibrational frequencies and the structural parameters effectively. The most stable conformer of the title compound was determined. The total electron density and molecular electrostatic potential surfaces of the molecule were constructed by using B3LYP/6-311++G(d,p) method to display electrostatic potential (electron+nuclei) distribution. The electronic properties HOMO and LUMO energies were measured. The lower energy band was assigned to the HOMO→LUMO transition. Natural bond orbital analysis of title molecule has been performed to indicate the presence of intramolecular charge transfer. Energies, relative stabilities, and dipole moments of title molecule were also compared and analyzed in the gas phase and in solvents. Furthermore, solvent effects on the geometry and vibrational frequency of 3M3HI4C were studied theoretically at the DFT/B3LYP level in combination with the conductor polarizable continuum model (C-PCM).

Theoretical study of the solvent effects on the molecular structure and vibrational spectra of 2-hydroxy-4-methyl-3-nitropyridine

Solvent effects on 2-hydroxy-4-methyl-3-nitropyridine molecule in different solvents (benzene, toluene, chloroform, acetone and water) were studied theoretically at the DFT/B3LYP level in combination with the conductor polarizable continuum model (CPCM) for the first time. Based on these results vibrational spectra were simulated. The role of the solvent polarity on the molecule stability, the optimized geometry, atomic charges (for charge distribution), dipole moments (for molecular charge transfer) and vibrational spectra belonging to title molecule was discussed in detail. It was found that the OH and NO2 stretching vibrations shift regularly to lower frequency value with higher IR intensity and the CH stretching vibrations shift to higher frequency value. The results obtained indicate not only the presence of the hydrogen bonding and strong intra-molecular charge transfer in the compound but the molecule stability with the solvent polarity, as well. Additionally, the complexes of title molecule−water were simulated to describe the effect of intermolecular hydrogen bonding on the molecular geometry and vibrational frequencies. It was found that the OH stretching vibrations shift regularly to lower frequency value with higher IR intensity due to the intermolecular H⋯O hydrogen bonds.

Computational study of the intramolecular proton transfer between 6-hydroxypicolinic acid tautomeric forms and intermolecular hydrogen bonding in their dimers

This paper is a density functional theory (DFT) calculation of intramolecular proton transfer (IPT) in 6-hydroxypicolinic acid (6HPA, 6-hydroxypyridine-2-carboxylic acid) tautomeric forms. The transition state for the enol-to-keto transition is reported in the gas phase and in four different solvents. The planar and non-planar dimer forms of 6HPA keto and enol, respectively, were also studied in the gas phase The IPT reactions and dimerization processes were studied at the B3LYP/6-31++G(d) level of the theory. The influence of the solvent on the tautomerization reaction of 6HPA was examined using the conductor-polarizable continuum model (CPCM). The IPT reaction in the gas phase is almost the same as in solution. The calculated dimerization energies show that the stability of 6HPA tautomer dimer structures is directly affected by the distance of intermolecular hydrogen bonding and electrostatic potential (ESP) value in the tautomer dimer.

Impact of Electron Acceptor on Three-Photon Absorption Cross-Section of the Fluorene Derivatives

Small three-photon absorption (3PA) cross-section values of present nonlinear organic molecules limit their practical applications. Although electron donors and electron acceptors have a great effect on 3PA cross-section, little is known about how the strength and situation of electron acceptors influence the 3PA cross-section value of a compound. The present work reports 3PA effects of two fluorene derivatives with symmetric D-π-π(A)-π-D archetype, which are named as 2,7-bis(4-methoxyphenylacetylene)-9-fluorenone (FATT) and 2,7-bis(4-methoxyphenylacetylene)-9-thoine-fluorene (TSATL). Large 3PA cross-section and ideal 3PA-induced optical limiting effects have been found in the two fluorene derivatives. The two molecules both have a different electron acceptor on the fluorene core, by which the 3PA cross-section value for FATT is enhanced by nearly 3-fold compared with that for TSATL. The mechanism of this significant enhancement in 3PA cross-section has been investigated by density functional theory (DFT) and configuration interaction singles (CIS) method with use of 6-311+G basis set in combination with conductor polarizable continuum model (CPCM). The theoretical results show that increase of electronegative character of the electron acceptor on the core is responsible for the increase of 3PA cross-section values of the two molecules.

Electronic Spectroscopy and Computational Studies of Glutathionylco(III)balamin

We have studied glutathionylcobalamin (GS-Cbl) by optical spectroscopy and with density functional theory (DFT) and time-dependent DFT (TD-DFT) electronic structure methods of truncated geometric models. We examined the geometric structure of the models by comparison of DFT calculations with recent high-resolution experimental X-ray structure data ( Hannibal, L. et al. Inorg. Chem. 2010, 49, 9921) for GS-Cbl, and we examined the TD-DFT excitation simulations by comparison of the models with measured optical spectra. The calculations employed the B3LYP hybrid functional and the nonhybrid BP86 functional in both vacuum and water (conductor polarized continuum model (cpcm)) with the 6-311G(d,p) basis set. The optimized geometric structure calculations for six truncated models were made by varying the chemical structure, solvent model, and the two DFT functionals. All showed similar geometry. Charge decomposition analysis (CDA) and extended charge decomposition analysis (ECDA), especially with BP86 shows the similar charge transfer nature of the Co-S bond in GS-Cbl and the Co-C bond in CH(3)Cbl. Mayer and Wiberg bond orders illustrate the similar covalent nature of the two bonds. Finally, absolute optical spectral simulation calculations were compared with the experimental UV-visible extinction spectrum and the electronic circular dichroism (ECD) differential extinction spectrum. The BP86 method shows more spectral features, and the best fit was found for a GS-Cbl model with 5,6-dimethylbenzimidazole at the BP86/6-311G(d,p) level with a water cpcm solvent model. The excited state transitions were investigated with Martin's natural transition orbitals (NTOs). The BP86 calculations also showed π bonding interactions between Co and the axial S of the GS- ligand in the molecular orbitals (MOs) and NTOs.

Theoretical study on the structures and electronic properties of oligo(p-phenylenevinylene) carboxylic acid and its derivatives: effects of spacer and anchor groups

The structural parameters of oligo(p-phenylenevinylene)carboxylic acid (OPV3–COOH) and its derivatives were optimized using the density functionals B3LYP, M06, M06-HF, M06-2X and the MP2 method on 6-31G(d) basis set level. The results show that the structure from B3LYP calculation is more planar than from M06, M06-2X, M06-HF, and MP2, respectively. The structures of OPV3–COOH obtained from various methods were used to calculate the electronic properties by time-dependent density functional theory calculation with the TD-CAM-B3LYP/6-311G(d,p) including conductor polarizable continuum model solvation to compare with the experimental absorption bands of this molecule. The excitation energies from the coplanar structure using M06-2X/6-31G(d) (406 nm) are closer to the experimental absorption data (430 nm) than the data from geometries optimized by M06-HF/6-31G(d) (362 nm) and MP/6-31G(d) (382 nm). Therefore, in this study, the M06-2X/6-31G(d) method was selected to investigate the effects of spacers for the structures and the electronic properties of OPV3–COOH and some derivatives. Spacer groups such as thiophene, dithiophene and vinylenethiophene linking between chromophore and the cyanoacrylic acid (–CNCOOH) anchor group can increase the electron transfer and expand the π-conjugated system to shift the absorption band into the visible light region. The more extended electron transfer and the red-shift of the absorption band for OPV3–COOH and OPV3–CNCOOH derivatives are desirable for absorbing sunlight and good employing as photo-sensitizer in dye-sensitized solar cell. Thiophene (OPV3–Th–CNCOOH), dithiophene (OPV3–diTh–CNCOOH) and vinylenethiophene (OPV3–viTh–CNCOOH) as spacer lead to the expansion of the π-conjugated system and to bathochromically shifted absorption spectra. Therefore, the modeling of side chain, spacer and anchor group in this study suggests new sensitizer compounds that enhance the efficiency of electron transfer and absorption of the sunlight for new synthetic materials.

UV/Vis Absorption, Emission Spectra and Two-Photo Absorption Cross Sections of 4-Dihydroquinolinone Derivatives

A series of 4-dihydroquinolinone derivatives were fully optimized by density functional theory (DFT), Hartree-Fock (HF) and Configuration Interaction Singlet (CIS) approaches. Absorption spectra, emission spectra and two-photon absorption cross sections were calculated by using time-dependent density functional theory and few-state model. Calculations were performed in the presence of solvent by using Conductor polarizable continuum model (CPCM). The molecular geometries, absorption spectra, emission spectra were in good agreement well with those experiment values. The absorption and emission peak red-shifted as a result of the extension of the conjugated structures. The introduction of heteroatoms such as F, Cl and Br gave rise to intramolecular transfer and the blueshift of the absorption and the emission spectra. The introduction of O or S atoms in two sides of molecules propelled the redshift of the absorption and emission maximum.

Theoretical investigation of solvent effects on tautomeric equilibrium of 2‐diazo‐4,6‐dinitrophenol

AbstractThe density functional theory has been used to study the tautomeric equilibrium of 2‐diazo‐4,6‐dinitrophenol(DDNP) in the gas phase and in 14 solvents at the B3LYP/6‐31G* level. The solvent effects on the tautomeric equilibria were investigated by the self‐consistent reaction field theory (SCRF) based on conductor polarized continuum model (CPCM) in apolar and polar solvents and by the hybrid continuum‐discrete model in protic solvent, respectively. Solvent effects on the computed molecular properties, such as molecular geometries, dipole moments, ELUMO, EHOMO, total energies for DDNP tautomers and transition state, tautomerization energies and solvation energies have been found to be evident. The tautomeric equilibrium of DDNP is solvent‐dependent to a certain extent. The tautomer I (cyclic azoxy form) is preferred in the gas phase, while in nonpolar solvents tautomer I and II (quinold form) exist in comparable amounts, and in highly polar solvents, the tautomeric equilibrium is shifted in favor of the more polar tautomer II. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011