Theoretical study of the role of solvent Stark effect in electron transitions (original) (raw)
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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.
Modeling Solvent Effects on Electronic Excited States
The Journal of Physical Chemistry Letters, 2011
W hile multiple absorption and emission spectroscopic experimental studies provide valuable information on the magnitude and dynamics of soluteÀsolvent coupling, calculations on electronic excited states in the condensed phase remain a major challenge to the theoretical chemistry community. The increased number of nuclear and electronic degrees of freedom relative to the gas phase makes accurate fully ab initio calculations on a condensed-phase system unfeasible long before the system can approach the bulk. One general approach to this type of problem is to separate a system into two parts, such that one (active, usually solute) part is treated by quantum mechanical (QM) techniques and the other (usually larger, solvent) part is calculated using classical (molecular) mechanics (MM). 2 The Hamiltonian of the system then consists of three termŝ
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.
Symmetry
The results obtained both in quantum chemical computation and in solvatochromic study of pyridinium di-carbethoxy methylid (PCCM) are correlated in order to estimate the electric dipole moment in the excited state of this molecule. This estimation is made by a variational method in the hypothesis that the molecular polarizability does not change in time of the absorption process. Ternary solutions of PCCM in protic binary solvents are used here, both establishing the contribution of each type of interaction to the spectral shift and to characterize the composition of the first solvation shell of PCCM. Results are compared with those obtained before for other binary solvents. The difference between the interaction energies in molecular pairs of PCCM-active solvent and PCCM-less active solvent was also estimated based on the cell statistical model of the ternary solutions.
Computer Physics Communications, 2003
ASEP/MD is a computer program designed to implement the Averaged Solvent Electrostatic Potential/Molecular Dynamics (ASEP/MD) method developed by our group. It can be used for the study of solvent effects and properties of molecules in their liquid state or in solution. It is written in the FORTRAN90 programming language, and should be easy to follow, understand, maintain and modify. Given the nature of the ASEP/MD method, external programs are needed for the quantum calculations and molecular dynamics simulations. The present version of ASEP/MD includes interface routines for the GAUSSIAN package, HONDO, and MOLDY, but adding support for other programs is straightforward. This article describes the program and its usage.
Journal of Chemical Theory and Computation, 2013
The inclusion of solvent effects in the calculation of excited states is vital to obtain reliable absorption spectra and density of states of solvated chromophores. Here we analyze the performance of three classical approaches to describe aqueous solvent in the calculation of the absorption spectra and density of states of pyridine, tropone and tropothione. Specifically, we compare the results obtained from quantum mechanics/polarizable continuum model (QM/PCM) versus quantum mechanics/molecular mechanics (QM/MM) in its electrostatic-embedding (QM/MMee) and polarizable-embedding (QM/MMpol) fashions, against full-QM computations, in which the solvent is described at the same level of theory as the chromophore. We show that QM/PCM provides very accurate results describing the excitation energies of ππ* and nπ* transitions, the last ones dominated by strong hydrogen-bonding effects, for the three chromophores. The QM/MMee approach also perform very well for both types of electronic transitions, although the description of the ππ* ones is slightly worse than that obtained from QM/PCM. The QM/MMpol approach performs as well as QM/PCM for describing the energy of ππ* states but it is not able to provide a satisfactory description of hydrogen-bonding effects on the nπ* states of pyridine and tropone. The relative intensity of the absorption bands is better accounted for by the explicit-solvent models than by the continuum-solvent approach.
The sequential QM/MM methodology is used to describe the solvent effects on the electronic absorption spectra of organic molecules in solution. The structure of the liquid is generated by Monte Carlo computer simulation. Configurations composed by the solute and several solvent molecules are selected for a posteriori quantum mechanical calculations of the spectra. Situations are considered where a large number of solvent molecules are necessary to describe the solvation problem. The examples considered here involve supermolecular systems composed of ca. 1500-2000 valence electrons, justifying the need for a semi-empirical approach. The electronic spectrum is then calculated using the INDO/CIS method. The solvatochromic shifts of pyrimidine in water and of beta-carotene in acetone and isopentane are considered. These exemplify the situations of a polar molecule
Chemical Physics Letters, 1993
A new approach is proposed to evaluate the solvent effect upon the electronic structure of a solute molecule in the liquid phase. The Hartrce-Fock and the extended reference interaction site model integral equations are solved in a self-consistent manner to simultaneously optimize the electronic structure of the solute., and the solvent distribution around it. The method is applied to a formaldehyde molecule in water. The result shows a clear indication of enhanced polarization of the solute molecule due to the solvent. The blue-shift induced by the solvent, which is observed in the absorption spectrum corresponding to the vertical 'A,+'AI transition, is reproduced.
Molecular orbital modeling of solvent effects on excited states of organic molecules
Journal of Molecular Structure-theochem, 1998
The excited states of organic molecules are considerably affected in most cases by their environment. A simple example of this phenomenon is the blue-shift effect shown by nπ* bands upon increasing the polarity of the solvent. The purpose of the current paper is to simulate the solvent effect on the excited states of two organic systems: furfural and 1-(N-methyl pyridyl)