Solvent effect on the absorption spectra of coumarin 120 in water: A combined quantum mechanical and molecular mechanical study (original) (raw)
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Luminescence : the journal of biological and chemical luminescence, 2017
The UV/Vis absorption and fluorescence characteristics of 3-cyano-7-hydroxycoumarin [CHC] and 7-amino-4-methyl-3-coumarinylacetic acid [AMCA-H] were studied at room temperature in several neat solvents and binary solvent mixtures of 1,4-dioxane/acetonitrile. The effects of solvent on the spectral properties are analyzed using single and multi-parameter solvent polarity scales. Both general solute/solvent interactions and hydrogen bond interactions are operative in these systems. The solvation of CHC and AMCA-H dyes in 1,4-dioxane/acetonitrile solvent mixtures has been studied. The solutes CHC and AMCA-H are preferentially solvated by acetonitrile and a synergistic effect is observed for both molecules in dioxane/acetonitrile solvent mixtures. In addition, using the solvatochromic method the ground- and the excited-state dipole moments of both the dyes were calculated. The ground- and excited-state dipole moments, absorption and emission maxima and HOMO-LUMO gap were also estimated t...
The Journal of Physical Chemistry A, 2005
The absorption spectra of aminocoumarin C151 in water and n-hexane solution are investigated by an explicit quantum chemical solvent model. We improved the efficiency of the frozen-density embedding scheme, as used in a former study on solvatochromism (J. Chem. Phys. 2005, 122, 094115) to describe very large solvent shells. The computer time used in this new implementation scales approximately linearly (with a low prefactor) with the number of solvent molecules. We test the ability of the frozen-density embedding to describe specific solvent effects due to hydrogen bonding for a small example system, as well as the convergence of the excitation energy with the number of solvent molecules considered in the solvation shell. Calculations with up to 500 water molecules (1500 atoms) in the solvent system are carried out. The absorption spectra are studied for C151 in aqueous or n-hexane solution for direct comparison with experimental data. To obtain snapshots of the dye molecule in solution, for which subsequent excitation energies are calculated, we use a classical molecular dynamics (MD) simulation with a force field adapted to first-principles calculations. In the calculation of solvatochromic shifts between solvents of different polarity, the vertical excitation energy obtained at the equilibrium structure of the isolated chromophore is sometimes taken as a guess for the excitation energy in a nonpolar solvent. Our results show that this is, in general, not an appropriate assumption. This is mainly due to the fact that the solute dynamics is neglected. The experimental shift between n-hexane and water as solvents is qualitatively reproduced, even by the simplest embedding approximation, and the results can be improved by a partial polarization of the frozen density. It is shown that the shift is mainly due to the electronic effect of the water molecules, and the structural effects are similar in n-hexane and water. By including water molecules, which might be directly involved in the excitation, in the embedded region, an agreement with experimental values within 0.05 eV is achieved.
Journal of the Physical Society of Japan, 2012
The solvent effect on the steady-state and time-resolved fluorescence spectra of coumarin 120 in water was studied utilizing a molecular dynamics simulation with combined quantum mechanical/molecular mechanical method. The constructed steady-state fluorescence spectra reproduced the Stokes shift of the experimental data. The solvent effects on the spectra were examined by constructing three different spectra: spectra using the entire system, spectra including water molecules only in the first solvent shell, and spectra excluding all water molecules. We found that the variation in C-C bond length makes the largest contribution to the solvent shift in the fluorescence spectrum, which indicates the importance of the electronic structure variation.
Spectrochimica Acta Part A-molecular and Biomolecular Spectroscopy, 2008
The effect of solvents on the absorption and emission spectra of ergone has been studied in various solvents at 298 K. The bathochromic shift was observed in absorption and fluorescence spectra with the increase of solvents polarity, which implied that transition involved was → *. And the normalized transition energy value E N T showed some scattering when plotted versus . The ground state and excited state dipole moments were calculated by quantum-mechanical second-order perturbation method as a function of the dielectric constant (ε) and refractive index (n). The result was found to be 1.435 D and 2.520 D in ground state and excited state respectively. And also, the density functional calculations were used to obtain the ground state and excited state dipole moments for it has proven to be suitable for calculating electronic excitation energy. And the result is consistent with the experimental.
Solvent effects on electronic spectra studied by multiconfigurational perturbation theory
International Journal of Quantum Chemistry, 1997
The complete active space CAS self-consistent field SCF method Ž. combined with multiconfigurational second-order perturbation theory CASPT2 and a Ž. self-consistent reaction field SCRF model is used to study the effect of solvation on excited states of different molecules such as acetone, pyrimidine, some aminobenzene derivatives, indole, and imidazole. The present SCRF model, in which the solute molecule is placed into a spherical cavity surrounded by a dielectric continuum, also includes a repulsive potential representing the solute᎐solvent exchange repulsion and considers the time dependence of the absorption process. In general, we find that our calculations do reproduce the trends observed in experiment but underestimate the solvatochromic shifts.
The Journal of Physical Chemistry A, 2002
In a time-resolved infrared spectroscopic study, the a 1 ∆ g f b 1 Σ g + absorption spectrum of molecular oxygen at ∼5200 cm -1 was recorded in 19 solvents using a step-scan Fourier transform infrared spectrometer. Solventdependent changes in the full width at half-maximum of this absorption band covered a range of ∼30 cm -1 and solvent-dependent changes in the position of the band maximum covered a range of ∼55 cm -1 . When considered along with solvent-dependent O 2 (a 1 ∆ g ) f O 2 (X 3 Σ g -) emission data, the current results identify features that must be incorporated in computational models of the interaction between oxygen and the surrounding solvent. In particular, data presented herein clearly demonstrate the importance of considering the influence of equilibrium and nonequilibrium solvation when interpreting the effect of solvent on transitions between the X 3 Σ g -, a 1 ∆ g , and b 1 Σ g + states of oxygen. The data indicate that the bandwidths of the O 2 (a 1 ∆ g ) f O 2 (b 1 Σ g + ) and O 2 (a 1 ∆ g ) f O 2 (X 3 Σ g -) transitions principally reflect the effects of equilibrium solvation, whereas the associated solvent-dependent spectral shifts reflect the effects of both equilibrium and nonequilibrium solvation. These general conclusions make it possible to resolve some long-standing problems associated with early attempts to interpret the effect of solvent on electronic transitions in oxygen
Conformation effects on the absorption spectra of macromolecules
Macromolecules, 1993
Applications of scattering theory to the estimation of absorption coefficientaof macromolecules yield values that are different from those obtained from the direct application of the Beer-Lambert law. These differences in absorption coefficients can be explained in terms of the size and optical properties of the macromolecules. Thia paper reports on the effects of the molecular conformation on the interpretation of the scattering-corrected absorption spectra of macromolecules. Using Monte Carlo simulations, the conformation of polymer chains modeled ae eelf-avoiding walke on a tetrahedral lattice has been investigated. It is demonstrated that the number of chromophores in the trajectory of the incident light varies ae a function ofthemolecularweight, ThroughanextensionoftheBeer-Lambertlaw,theeffectofelignmentofchromophoric groups is explored and the resulta are compared with experimentally measured spectra. It is concluded that information on the conformation of macromolecules is contained in the Wyie spectra and that this information may be quantitatively extracted.
Solvent Perturbation of the Electronic Intensity of Solvated Absorbing Molecules
Physical Chemistry, 2012
In this paper, we present a general expression originating from quantum-mechanical perturbation treatment of electronic intensities and Hamiltonian operators for the system (H A and H B) of an absorber and a perturber respectively. The expression is related to the Longuet-Higgins' definition of solute-solvent interaction and fitted into linear regression mode for the determination of transition polarizabilities of 9H-xanthene, 9H-xathone and 9H-xanthione. The result conforms to those earlier obtained when all possible interaction modes are considered.
Theory of solvent effects on electronic spectra
Journal of Molecular Structure: THEOCHEM, 1991
We describe theory and review theoretical investigations of solvent effects on electronic spectra. We review briefly five main models for such investigations, namely the thermochemical, supermolecular, dielectric, reaction field and the statistical models. The last two models are particularly emphasized and are reviewed in more detail. The reaction field theory is described with respect to solvent response and solvent energy. The cavity model is outlined as well as the self-consistent reaction field method (SCRF') and its multi-configurational formulation (MCSCRF') . Examples of the application of these models are given by studies of solvent effects on photoelectron and Auger spectra of ionic and molecular solutions. We also review solvent theory and calculations for excitation spectra and solvatochromatic shifts, illustrated with the radiative deactivation of singlet molecular oxygen as a specific example.
The Journal of Physical Chemistry A, 1999
A comparison of the solvation/spectral-response functions obtained by two independent techniques, the singlewavelength and spectral-reconstruction methods, is reported. Determination of the best wavelengths for application of the linear-single-wavelength approximation for the solute coumarin 153 (C153) is achieved using radiative rate data and steady-state emission spectra in a series of 36 different solvents at room temperature. The optimal linear wavelength is found to be 555 nm. (This wavelength, which is on the red side of the spectrum, yields superior results when compared to the more traditional choice of 470-480 nm, on the blue side.) Response functions determined using both 560-and 470-nm observation wavelengths are compared to previously reported spectral-reconstruction results in 24 solvents. A comparison of the characteristic times indicates that the linear-single-wavelength method can be used to predict solvation times with an accuracy of roughly (30-40% (1 standard deviation) using suitably scaled data collected at ∼560 nm. Application of a nonlinear version of the single-wavelength method does not provide increased accuracy.