Polarizable Continuum Model Model Research Articles

Infrared bands of formaldehyde dissolved in liquid krypton at cryogenic temperatures and the vibrational modes ν1, ν2, and ν5 of H2CO in comets and interstellar clouds

The infrared spectra of formaldehyde (H2CO) dissolved in liquid krypton between 125 K and 137 K have been obtained using a Fourier transform infrared spectrophotometer and a low temperature cryostat. Backing pressures higher than 1.5 atm were necessary to liquefy Kr above 120 K. Monomeric formaldehyde in gas phase was prepared by thermal decomposition of para-formaldehyde. Peak positions (ν), wavenumber shifts between the gas and liquid solution spectra (Δν), and full widths at half maximum (fwhm) are reported. The H2CO vibrational frequencies in liquid Kr are slightly lower than the gas phase frequencies at room temperature because of the inertness of the solvent. The Gaussian 16 software package is used to determine the geometry and lowest energy of H2CO at room temperature and at the temperature of the experiment. Fundamental harmonic and anharmonic vibrational frequencies and relative intensities are calculated. The influence of the solvent on fundamental vibrational frequencies is studied using the polarizable continuum model (PCM). When used in conjunction with calculated anharmonic frequencies, the PCM model shows qualitative agreement with experimental frequency shifts and relative intensities in liquid Kr. The presence of H2CO in space is discussed in reference to the ν1 and ν5 absorption bands observed in comets, the ν1 and ν2 absorptions in interstellar clouds, and the lack of detection of the ν4 and ν6 bands of H2CO in the atmosphere of Titan. The carbonyl stretching mode ν2 is suggested as a possible candidate for confirmation and identification of H2CO in space due to its larger strength in comparison to the other modes that have been studied at low temperatures and its characteristic frequency that is completely removed from CO2, CO, H2O and CH3OH vibrational modes.

Multireference Perturbation Theory Combined with PCM and RISM Solvation Models: A Benchmark Study for Chemical Energetics.

The polarizable continuum model (PCM) has been one of the most widely used approaches to take into account the solvation effect in quantum chemical calculations. In this paper, we performed a series of benchmark calculations to assess the accuracy of the PCM scheme combined with the second-order complete-active-space perturbation theory (CASPT2) for molecular systems in polar solvents. For solute molecules with extensive conjugated π orbitals, exemplified by elongated conjugated arylcarbenes, we have incorporated the ab initio density matrix renormalization group algorithm into the PCM-CASPT2 method. In the previous work, we presented a combination of the DMRG-CASPT2 method with the reference interaction site model (RISM) theory for describing the solvation effect using the radial distribution function and compared its performance to the widely used density-functional approaches (PCM-TD-DFT). The work here allows us to further show a more thorough assessment of the RISM model compared to the PCM with an equal level of the wave function treatment, the (DMRG-)CASPT2 theory, toward a high-accuracy electronic structure calculations for solvated chemical systems. With the exception that the PCM models are not capable of properly describing the hydrogen bondings, accuracy of the PCM-CASPT2 model is in most cases quite comparable to the RISM counterpart.

Vibratile Dihydrophenazines with Controllable Luminescence Enabled by Precise Regulation of π-Conjugated Wings

Vibratile Dihydrophenazines with Controllable Luminescence Enabled by Precise Regulation of π-Conjugated Wings

Exploring the electrochemical windows of Triazolium-based [PhMTZ][X1–7] ionic liquids (ILs) at MP2/Aug-cc-pVDZ level of theory by using thermochemical cycle in IL media

Abstract In the present study, potentials of oxidation (E°OX) and reduction (E°red), and electrochemical windows (ECWs) of the 1-methyl-4-phenyl 1,2,4 triazolium-based [PhMTZ][X1–7] (X1–7 = CF3COO−, NO3−, CH3SO3−, TfO−, NTf2−, BF4− and PF6−) ILs with respect to a Li+/Li reference electrode were explored. To predict the accurate values of the thermodynamic properties of ILs, at first, dielectric constants and electronic polarizability of ILs were calculated at the MP2/Aug-cc-pVDZ level of theory. The calculated dielectric constants were used in PCM model for computing thermodynamic properties of ILs. The electrochemical properties were obtained by applying the polarizable continuum model (PCM) at the MP2/Aug-cc-pVDZ level of theory by using the thermochemical cycle (TCC). It is found that [PhMTZ]+ cation is less stable than the anions against the reduction and BF4− and PF6− anions are more stable than other anions versus oxidation. The TCC and HOMO/LUMO based ECW values of the [PhMTZ][X1–7] ILs are in the order of [PhMTZ][X1]

Vibrational fundamental and overtone spectra of C2H4 in cryogenic liquid solutions.

Vibrational Fundamental and overtone transitions of C2H4 around the Δυ=1-3 in liquid Ar, Kr, Xe and N2 solutions have been obtained using a low temperature cryostat and a Fourier transform infrared spectrophotometer for wavenumbers between 800 and 10,000cm-1. The visible CH spectra for Δυ=6 of ethylene in cryogenic solutions of the same solvents and liquid ethane have been measured with a low temperature cell and the thermal lens technique. Spectra in solutions show great simplification of the bands with respect to gas phase absorption bands. Assignments have been made based on gas phase transitions. Peak positions (ν), wavenumber shifts (Δν), and full widths at half maximum (Δω1/2) are reported. Changes of C2H4 frequencies in liquid Ar, Kr, and Xe seem to correlate with an increase in molar volume, dielectric constant, temperature, and polarizability of the solvents. Influence of the solvent on some fundamental vibrational frequencies are explored using the Onsager model and the polarizable continuum model (PCM). When used in conjunction with calculated anharmonic frequencies, the PCM model shows qualitative agreement with frequency shifts.

Synthesis, Spectroscopic Properties, Quantum Chemical Calculations, and Biological Activities of 2-{[5-(2-Fluorophenyl)-4-(4-methylphenyl)-4H-1,2,4-triazol-3-yl]sulfanyl}-1-[3-methyl-3-(2,4,6-trimethylphenyl)-cyclobutyl]ethan-1-one

2-{[5-(2-Fluorophenyl)-4-(4-methylphenyl)-4H-1,2,4-triazol-3-yl]sulfanyl}-1-[3-methyl-3-(2,4,6-trimethylphenyl)cyclobutyl]ethanone was synthesized and characterized by spectral techniques and quantum chemical calculations. The molecular geometry, vibrational frequencies, and gauge-including atomic orbital (GIAO) 1H and 13C NMR chemical shifts of the title compound in the ground state were calculated using the density functional method (B3LYP) with the 6–311G(d, p) basis set, and its electronic absorption spectra were calculated by the TD-DFT method based on the B3LYP/6-311G(d, p) level optimized structure in ethanol by using the PCM model. The calculated results showed that the optimized geometry well reproduces the theoretical vibrational frequencies, and the calculated chemical shifts were in a good agreement with the experimental values. The energetic behavior of the title compound was examined using the B3LYP method with the 6-311G(d, p) basis set in the framework of the Onsager and polarizable continuum model (PCM). In addition, DFT calculations of frontier molecular orbitals were carried out at the B3LYP/6-311G(d, p) level of theory. The title compound showed antibacterial and antioxidant activities at different levels.

Effect of a Hydrogen Bond on Molecular Probing Properties in the Solvent.

Hydrogen bond (HB) is of an important factor on theory. In this work, the effect of a solvent on the performance of a newly synthesized fluorescent probe for detecting endogenous ONOO- is studied by using four different solvent models, noted as polarizable continuum model (PCM), ONIOM, HB, and HB + PCM models, respectively, where HB contribution is thus given special attention. The theoretical results show that the absorption and emission properties of the probe are obviously influenced by the HB; for example, the HB + PCM model including both short- and long-range interactions between the solute and solvent molecules gives the exact description on the solvent effect. In particular, the responsive mechanism of the probe for sensing ONOO- is explored by analyzing the charge variations between the excited states and ground states of the free molecules and their reaction products. It is demonstrated that the mechanism is attributed to an intramolecular charge transfer, where the HB has an important contribution. Moreover, the influence of HB on a two-photon absorption cross section has been considered. Our investigation reveals that the HB has an important influence on the optical properties and responsive mechanism of the fluorescent probe, and it must be considered for theoretical calculations.

The amidine formed by tacrine and saccharin revisited: An ab initio Investigation of Structural, Electronic and Spectroscopic Properties

Computational study of tacrine and saccharin and their amidine complex (TacSac) was peformed by ab initio calculations including electron correlation. Structure, UV-Vis spectra and charge distribution of the amidine (TacSac) were investigated using ground state geometries optimized at MP2/6-311++G(d,p) level. The effects of solvent was investigated using polarizable continuum model (PCM) in conjunction with the solvation model based on density (SMD) approach. TacSac geometry remained same in gas phase and in H2O both with PCM and SMD models in contrast to former DFT results. The amidine is calculated to be stable indicating that former DFT calculations underestimated the stability of the investigated amidine. UV-Vis spectra and electronic transitions were calculated at CIS/6-311++G(d,p), B3LYP/6-311++G(d,p) and CAM-B3LYP/6-311++G(d,p) levels of theory and B3LYP gave the best results. TacSac has a peak at a higher wavelength enabling S0→S1 transition with a lower energy. S0→S1 transition corresponds to full charge transfer between HOMO and LUMO orbitals of TacSac in H2O. The ab initio results indicate that the TacSac system can be synthesized with an easy condensation reaction, and that the amidine product is a potential candidate for photochemical charge-transfer systems.

Comparison of Polarizable Continuum & Quantum Mechanics/Molecular Mechanics Models with Series of Tripeptides (AXA)

In biomolecule simulations solvation is a key factor in representing experimental conditions. Recent studies use models like Quantum Mechanics and Molecular Mechanics (QM/MM) and Polarizable Continuum Model (PCM) to attempt to simulate solvent effects on spectra. For proteins and peptides vibrational analyses primarily focuses on amide I (due to its isolation and strong dipole moment) to determine information about the secondary structure (α-helix, β-sheet, PPII). In this study we compare the QM/MM and PCM models with a focus on amide I at ∼1650 cm−1 (mainly amide C=O stretch) and also extended to lower energy amide II (∼ 1550 cm−1) in order to gain insight into the effectiveness of either method. We modeled a series of tripeptides (AXA: where X=A, E, S, W) and capped at N- and C- termini to yield Ac-Ala-Xxx-Ala-NH2. For QM/MM studies, we first sampled the conformations with an explicit solvent using Charmm 36 force field. The simulations were executed for 20 ns using periodic boundary conditions, with constant pressure and temperature (NPT ensemble) at 300 K and 1 atm. We then obtained the most preferable conformation (which is PPII-like) and extracted the geometry for both PCM and QM/MM level calculation to generate IR and VCD spectra. Furthermore, PCM Model was computed with an ideal PPII-like conformation (−78,149,180) to compare with preferable conformation obtained from MD simulation. The geometry was constrained (in terms of φ, ψ torsional angles) and prepared for optimization. With PCM model we use an implicit solvent while in QM/MM we use an explicit solvation shell of 10A. All calculations were fully optimized across all coordinates except (φ, ψ, ω, which were fixed) at the DFT BPW91/6-31G∗∗ level of theory. By observing amide I and amide II, accurate inferences about the different types of theory were made.

Crystal structure, spectroscopic investigations and quantum chemical computational study of 5-(diethylamino)-2-((3-nitrophenylimino)methyl)phenol

The Schiff base compound, 5-(diethylamino)-2-((3-nitrophenylimino)methyl)phenol, C17H19O3N3, was synthesized and characterized by IR, UV–Vis and single-crystal X-ray diffraction (XRD) technique. The title compound prefers enol tautomeric form in solid state as to X-ray, IR and UV–Vis spectra results. Also, using the TD-DFT method, the electronic absorption spectra of the title compound was computed in both the gas phase and ethanol solvent. The calculated results support that the enol form is more stable than keto form. The molecular geometry from the X-ray single-crystal determination of the title compound in the ground state was compared at the B3LYP and B3PW91 levels of the density functional method (DFT) with the 6-311 + G(d,p) basis set. The harmonic vibrational frequencies of the title compound were calculated using the B3LYP and B3PW91 methods with the 6-311G+(d,p) basis set. The calculated results were compared with the experimental determination results of the compound. The potential energy surface scans about important torsion angels were performed by B3LYP/6-311 + G(d,p) level of theory for the title compound. The energetic behaviors of the title compound in the solvent media were also examined using the B3LYP and B3PW91 methods with the 6-311 + G(d,p) basis set applying the Onsager and the polarizable continuum model (PCM). Besides, the molecular electrostatic potential map (MEP), frontier molecular orbitals (FMO) analysis and thermodynamic properties for the title compound were obtained with the same levels of theory. The nonlinear optical properties (NLO) of the title compound were performed in the solvent media using the B3LYP and B3PW91 methods with the 6-311 + G(d,p) level using the PCM model.

Combined theoretical and experimental approaches for development of squaraine dyes with small energy barrier for electron injection

A series of far-red sensitizing squaraine dyes has been systematically designed and synthesized in order to correlate the theoretically calculated values with their corresponding experimental parameters. Efforts have been directed towards determining the minimum thermodynamic energy barrier for the electron injection in the nanoporous TiO2 by logical molecular design. Theoretical calculations using Gaussian program package were performed for ground and excited states in both of the isolated gaseous state as well as in solution including the solvent effect using a self-consistent reaction field polarizable continuum model (PCM). Implementation of the PCM model or use of LSDA functional under TD-DFT calculations gives much better results for energetics as well as absorption maximum for all of the sensitizers used in this work. Newly designed symmetrical squaraine dye SQ-5 exhibits a minimum energy barrier of 0.16eV for electron injection and shows photon harvesting behavior in far-red region with external photoconversion efficiency of 2.02% under simulated solar irradiation.

Three-dimensional reference interaction site model solvent combined with a quantum mechanical treatment of the solute

We implemented and applied a hybrid approach for modeling the solvation of molecules where we combined a three-dimensional reference interaction site model (3D RISM) with quantum mechanical (QM) calculations of the solute. The electrostatic potential induced by the solute is derived directly from its electron density. For neutral solutes, we analyzed the accuracy of calculated solvation free energies which is mainly determined by the cavity formation energy. In an aqueous medium the solute electronic structure relaxation also has a noticeable influence on the results of SCF-RISM calculations. We apply a known partial molar volume correction for which we give an alternative interpretation. The results of this hybrid model agree well with experiment and results of a polarizable continuum model (PCM). As a model with an atomic solvent representation, RISM accounts for the effect of discrete hydrogen bonds which in PCM models are included on average only.

Dual fluorescence of 4-(dimethylamino)-pyridine: a comparative linear response TDDFT versus state-specific CASSCF study including solvent with the PCM model

Two different theoretical approaches have been used for the description of the experimentally observed dual luminescence of 4-(dimethylamino)pyridine (DMAP), introducing solvent effects with the polarizable continuum model (PCM), which seems needed to represent the dual fluorescence in polar media. These approaches are the linear response time-dependent density functional theory (TDDFT) and the state-specific complete active space self-consistent field. Both levels of theory represent the expected planar high-energy and the twisted intramolecular charge transfer (ICT) low-energy excited-state structures in the presence of solvent (toluene and acetonitrile). The comparison between both approaches shows that the main distortion of the ICT state is similar for both cases, i.e. twisting to almost 90o of the pyridine ring and the dimethylamino planes, but that other secondary distortions are slightly different. In the case of the TDDFT approach, the geometry optimizations of DMAP in the ground and excited states have been carried out using the conventional linear response approach (LR-PCM) for the solvent inclusion. The LR-PCM and the specific state (SS-PCM) approaches have been used for the prediction of the excitation and emission energies of DMAP in toluene and acetonitrile. The prediction of the emission energies at TDDFT/LR-PCM and CASPT2/PCM (complete active space perturbation theory) levels agrees with the experimental ones.

Medium Effect on Solvation Free Energy, Dipole Moment and Molecular Reactivity of Naproxen

In this paper, a computational study of medium effect on solvation free energy, dipole moment and different molecular properties like global reactivity descriptors (chemical hardness, softness, chemical potential, electronegativity, electrophilicity index) of naproxen have been reported. Hartee–Fock (HF) and Becke, 3-parameter, Lee-Yang-Parr (B3LYP) level of theory with 6-31G(d) and 6-31G(d,p) basis sets were applied for gas phase and solution. The solvation free energy, dipole moment and molecular properties were calculated by employing two solvation models namely polarizable continuum model (PCM) and Solvation Model on Density (SMD). For all levels of theory, the solvation free energies were gradually increased in going from lower to higher dielectric constant for PCM, but opposite result was observed in case of SMD model. However, with SMD, the solvation free energies were higher than that of PCM in all the solvent systems. The dipole moment of naproxen was found to be increased when going from non-polar to polar solvents for both PCM and SMD model. The dipole moment of naproxen was higher in different solvents than that of the gas phase. Moreover, Ongoing from non-polar to polar solvent the chemical potential, electronegativity and electrophilicity index were increased regardless of the solvation models, basis sets and level of theories used. On the other hand, no noticeable medium effect was observed on chemical hardness and softness. The results obtained in this study may lead to understand the stability and reactivity of naproxen and the results will be of assistance to use the title molecule in reaction intermediates and pharmaceuticals.

Solvent Effects on Excited-State Structures: A Quantum Monte Carlo and Density Functional Study

We present the first application of quantum Monte Carlo (QMC) in its variational flavor combined with the polarizable continuum model (PCM) to perform excited-state geometry optimization in solution. Our implementation of the PCM model is based on a reaction field that includes both volume and surface polarization charges and is determined self-consistently with the molecular wave function during the QMC optimization of the solute geometry. For acrolein, acetone, methylenecyclopropene, and the propenoic acid anion, we compute the optimal exited-state geometries in water and compare our results with the structures obtained with second-order perturbation theory (CASPT2) and other correlated methods, and with time-dependent density functional theory (TDDFT). We find that QMC predicts a structural response to solvation in good agreement with CASPT2 with the only exception of the π → π* state of acrolein where the robustness of the QMC geometry must be contrasted to the sensitivity of the perturbation result to the details of the calculation. As regards TDDFT, we show that all investigated functionals systematically overestimate the geometrical changes from the gas phase to solution, sometimes giving bond variations opposite in trend to QMC.

Mechanistic Study of the Deamidation Reaction of Glutamine: A Computational Approach

Glutamine--a popular nutritional supplement, non-toxic amino acid, and an essential interorgan and intercellular ammonia transporter--can destroy the neurons' mitochondria. When glutamine enters (like a Trojan horse) into the mitochondria, in the presence of glutaminase, it reacts with water and yields glutamate and excess ammonia which opens gates in the membrane of the mitochondria and thereby destroys it. The mechanistic details underlying the molecular basis of the catabolic production of excess ammonia remain unclear. In the present paper, both 5-oxoproline-mediated and direct pathways for glutamine deamidation are studied using wave function and density functional theories. The mechanisms are studied both in the gas phase and in aqueous solution using the polarizable continuum model (PCM) and solvent model on density (SMD) solvation models. Among three glutamine deamidation pathways, a two-step pathway, GDB, shows the lowest gas phase barrier height of 189 kJ/mol with the G3MP2B3 level of theory. Incorporation of solvent through PCM and SMD models reduces the barrier height to 183 and 174 kJ/mol, respectively. For the hydrolysis of 5-oxoproline, a two-step mechanism, pathway PH-B, provides a lower gas phase energy barrier (187 kJ/mol) compared to one-step (201 kJ/mol) and three-step (227 kJ/mol) pathways at G3MP2B3. Although direct hydrolysis with OH(-), pathway DHE, has the lowest gas phase barrier of 135 kJ/mol, the solvent has little effect on the barrier. For the direct hydrolysis with OH(-)/H2O, pathway DHF, the overall barrier is 143 kJ/mol, in the gas phase at G3MP2B3. In aqueous solution, the overall barrier decreases to 76 and 75 kJ/mol with PCM and SMD, respectively, at B3LYP/6-31+G(d,p), making this the most plausible mechanism. Compared to PCM, SMD predicts lower barriers for nearly all pathways investigated.

Theoretical investigation of the thermodynamic structures and kinetic water-exchange reactions of aqueous Al(III)–salicylate complexes

Density functional theory (DFT) calculations were performed on the structures and water-exchange reactions of aqueous Al(III)–salicylate complexes. Based on the four models (gas phase (GP); polarizable continuum model (PCM), which estimates the bulk solvent effect; supermolecule model (SM), which considers the explicit solvent effect, and supermolecule–polarizable continuum model (SM–PCM), which accounts for both types of solvent effects), we systematically conducted this study by examining three different properties of the complexes. (1) The microscopic properties of the aqueous Al(III)–salicylate complexes were studied by optimizing their various structures (including the possible 1:1 mono- and bidentate complexes, cis and trans isomers of the 1:2 bidentate complexes and 1:3 bidentate complexes) at the B3LYP/6-311+G(d, p) level. (2) The 27Al and 13C NMR chemical shifts were calculated using the GIAO method at the HF/6-311+G(d, p) level. The calculation results show that the values obtained with the SM–PCM models are in good agreement with the experimental data available in the literature, indicating that the models we employed are appropriate for Al(III)–salicylate complexes. (3) The water-exchange reactions of 1:1 mono- and bidentate Al(III)–salicylate complexes were simulated using supermolecule models at the B3LYP/6-311+G(d, p) level. The logarithm of the water-exchange rate constant (logkex) of the 1:1 bidentate complex predicted using the “logkex–dAl–OH2” correlation is 4.0, which is in good agreement with the experimental value of 3.7, whereas the calculated range of logkex of the 1:1 monodentate complexes is 1.3–1.9. By effectively combining the results for the thermodynamic static structures with the simulations of the kinetic water-exchange reactions, this work promotes further understanding of the configurations and formation mechanism of Al(III)–salicylate complexes.

TD-DFT and DFT/MRCI study of electronic excitations in Violaxanthin and Zeaxanthin

We report vibrationally broadened Franck–Condon (FC) spectra of Violaxanthin (Vx) and Zeaxanthin (Zx) for the lowest-energy 1Ag→1Bu band that arises from the bright HOMO→LUMO single-electron excitation. Geometries were optimized using standard (1Ag) and time-dependent (1Bu) density functional theory (DFT) at the (TD-)CAM-B3LYP/6-31G(d) level, both in the gas phase and in acetone using a polarizable continuum model (PCM). DFT/MRCI multireference calculations were performed at the optimized (TD)-CAM-B3LYP structures to evaluate the energies of doubly excited states that are not accessible to linear response TD-DFT theory. The FC spectra were calculated using the time-independent (TI) scheme. The calculated spectra of Vx and Zx are very similar, with a red shift of about 0.1eV for Zx relative to Vx, which is in agreement with the experimental data. The predicted spectral peaks of Vx and Zx deviate from experiment by less than 0.1eV when performing the calculations in the gas phase. In the presence of acetone (PCM model), there are larger deviations so that a state specific correction scheme needs to be applied, which accounts for non-equilibrium solvent relaxation. The 1Ag→1Bu vertical absorption energies and the corresponding vertical fluorescence energies from TD-CAM-B3LYP and DFT/MRCI agree reasonably well. The DFT/MRCI absorption and fluorescence energies for the doubly excited 2Ag and 2Bu states are found to be rather sensitive to the underlying geometry, in particular to the bond length alternation in the polyene chain. In acetone (PCM), Vx and Zx show little bond alternation, and thus the doubly excited Bu state becomes the lowest excited Bu state. (TD)-CAM-B3LYP appears to be suitable for generating realistic geometries for higher-level calculations in such molecules.

Conformational Preference of Fused Carbohydrate-Templated Proline Analogues—A Computational Study

The structure of fused C-glucosylproline hybrid (GlcProH) has been studied in detail computationally. A systematic molecular mechanics/Monte Carlo search has been performed in order to cover the entire conformational space of GlcProH. This has been followed by density-functional (DFT B3LYP) calculations in the gas phase and in aqueous solution, using the polarizable continuum model (PCM). In the gas phase, a large excess of the cis conformation with respect to the prolyl amide bond is found. This is reversed in aqueous solution where the calculations show 80% trans conformers, which is in accordance with experimental data. Thus, the PCM model is capable of accurately predicting cis-trans ratios. The free energy of solvation is not correlated with the dipole moment. Hence, a model (such as PCM) is required that takes into account the complete charge distribution. The reversal of the cis-trans ratio between gas phase and solution also emphasizes the effects of different free energies of solvation for the distinct conformers. Nevertheless, the energy difference between the cis and trans conformers is very small in solution (0.18 kcal/mol). Intramolecular hydrogen bonding is found to stabilize the cis conformers exclusively, which is a result of the rigid geometry of the fused rings. This can be contrasted to related more flexible molecules that show hydrogen bonding for both cis and trans isomers. The hydrogen bonding is at least partially responsible for the preferential stabilization of the cis conformers in the gas phase and a very small cis-trans energy difference in solution.

Mechanisms for Solvatochromic Shifts of Free-Base Porphine Studied with Polarizable Continuum Models and Explicit Solute-Solvent Interactions.

Solvatochromic shifts of free-base porphine in the Q-band and B-band were studied using the polarizable continuum model (PCM) and explicit solvent molecules employing time-dependent density functional theory (TDDFT) and the symmetry-adapted cluster-configuration interaction (SAC-CI) method. The state-specific (SS) and linear-response (LR) methods were examined in the PCM calculations. These models involve different types of solute-solvent interactions. The LR PCM and explicit solvation models reproduced the experimentally observed trends of the solvatochromic shifts, while the SS PCM failed to reproduce the experimental findings. The origin of the solvatochromic shifts of free-base porphine was dispersive interactions between the solute and solvent. Specific solute-solvent interactions would be important for a decrease of the splitting width between Q-bands. Based on the Casimir-Polder formula and a decomposition analysis, it was found that the dominant part of the solute-solvent interactions can be considered using independent particle approximations.