Modeling solvent effects on chiroptical properties.

In this article, the most advanced extensions of solvation models to chiroptical properties of solvated systems will be reviewed. The main aspects determining the complex phenomenon of solvation will be first discussed in terms of the physical interactions beyond them and successively translated in a computational language introducing the specific models. A particular attention will be devoted to the family of solvation models which couple a quantum-mechanical description of the molecular solute and a continuum description of the solvent.

Structure versus solvent effects on nonlinear optical properties of push-pull systems: a quantum-mechanical study based on a polarizable continuum model.

A quantum mechanical investigation on the effects of the solvent and the structure on nonlinear optical activity of a class of merocyanine compounds has been conducted. The interplay of the two effects on the first hyperpolarizability, computed at density functional theory and second-order Møller-Plesset level, has been analyzed in combination with ground state properties and geometries and excited state energies and dipoles. A critical analysis of the simplified two-level model has also been presented.

Structures and properties of electronically excited chromophores in solution from the polarizable continuum model coupled to the time-dependent density functional theory.

This paper provides an overview of recent research activities concerning the quantum-mechanical description of structures and properties of electronically excited chromophores in solution. The focus of the paper is on a specific approach to include solvent effects, namely the polarizable continuum model (PCM). Such a method represents an efficient strategy if coupled to proper quantum-mechanical descriptions such as the time-dependent density functional theory (TDDFT).

On the performance of continuum solvation methods. A comment on "Universal approaches to solvation modeling".

In a recent Account, Cramer and Truhlar presented a comparison between the SM8 method and standard versions of other continuum solvation models implemented in widely available quantum mechanical programs. In that Account, the SM8 model was found to lead to "considerably smaller errors for aqueous and nonaqueous free energies of solvation for neutrals, cations, and anions, with particularly good performance for nonaqueous data". Here, we demonstrate that competing solvation methods are indeed as accurate as the SM8 method, if they are applied with the same rigor.

Response of Scalar Fields and Hydrogen Bonding to Excited-State Molecular Solvation of Carbonyl Compounds.

An attempt has been made to understand the mechanism of excited-state molecular solvation and its effect on hydrogen bonding in carbonyl compounds in aqueous solution. The correlation between solvation and electronic transitions has been investigated by comparing results obtained either with a supermolecular description in terms of hydrogen-bonded clusters or with a combined method embedding such clusters with a polarizable continuum dielectric mimicking the bulk water. Popular scalar fields such as molecular electrostatic potential and molecular electron density have been used as useful tools to probe the changes in the hydrogen bonding passing from ground to excited states in the gas as well as solvent phase.

How the environment controls absorption and fluorescence spectra of PRODAN: a quantum-mechanical study in homogeneous and heterogeneous media.

The spectroscopic behavior of 6-propionyl-2-(N,N-dimethyl)aminonaphthalene (PRODAN) is investigated in different environments, ranging from homogeneous solutions of different polarities to diffuse interfaces mimicking membranes. The variety of experimental data as well as computational results present in the literature still do not clarify the nature of the emission process; in particular, it is not well-established whether fluorescence in such a molecule occurs from a planar or from a twisted intramolecular charge transfer state. The first part of the work is thus devoted to better understand how the electronic transition processes occur in homogeneous solvents.

How solvent controls electronic energy transfer and light harvesting.

The way that solvent (or host medium) modifies the rate of electronic energy transfer (EET) has eluded researchers for decades. By applying quantum chemical methods that account for the way solvent (in general any host medium including liquid, solid, or protein, etc.) responds to the interaction between transition densities, we quantify the solvent screening.

Dispersion and repulsion contributions to the solvation free energy: comparison of quantum mechanical and classical approaches in the polarizable continuum model.

We report a systematic comparison of the dispersion and repulsion contributions to the free energy of solvation determined using quantum mechanical self-consistent reaction field (QM-SCRF) and classical methods. In particular, QM-SCRF computations have been performed using the dispersion and repulsion expressions developed in the framework of the integral equation formalism of the polarizable continuum model, whereas classical methods involve both empirical pairwise potential and surface-dependent approaches. Calculations have been performed for a series of aliphatic and aromatic compounds containing prototypical functional groups in four solvents: water, octanol, chloroform, and carbon tetrachloride.

Solvation dynamics in acetonitrile: a study incorporating solute electronic response and nuclear relaxation.

The solvent reorganization process after electronic excitation of a polar solute in a polar solvent such as acetonitrile is related mainly to the time evolution of the solute-solvent electrostatic interaction. Modern laser-based techniques have sufficient time resolution to follow this decay in real time, providing information to be confirmed and interpreted by theories and models. We present here a study aimed at the investigation of the different steps involved in the process taking place after a vertical S(0) --> S(1) excitation of a large size chromophore, coumarin 153 (C153), in acetonitrile, from both the solute and the solvent points of view.

Formation and relaxation of excited states in solution: a new time dependent polarizable continuum model based on time dependent density functional theory.

In this paper a novel approach to study the formation and relaxation of excited states in solution is presented within the integral equation formalism version of the polarizable continuum model. Such an approach uses the excited state relaxed density matrix to correct the time dependent density functional theory excitation energies and it introduces a state-specific solvent response, which can be further generalized within a time dependent formalism. This generalization is based on the use of a complex dielectric permittivity as a function of the frequency, epsilonomega.

Geometries and properties of excited states in the gas phase and in solution: theory and application of a time-dependent density functional theory polarizable continuum model.

In this paper we present the theory and implementation of analytic derivatives of time-dependent density functional theory (TDDFT) excited states energies, both in vacuo and including solvent effects by means of the polarizable continuum model. The method is applied to two case studies: p-nitroaniline and 4-(dimethyl)aminobenzonitrile. For both molecules PCM-TDDFT is shown to be successful in supporting the analysis of experimental data with useful insights for a better understanding of photophysical and photochemical pathways in solution.

A time-dependent polarizable continuum model: theory and application.

This work presents an extention of the polarizable continuum model to explicitly describe the time-dependent response of the solvent to a change in the solute charge distribution. Starting from an initial situation in which solute and solvent are in equilibrium, we are interested in modeling the time-dependent evolution of the solvent response, and consequently of the solute-solvent interaction, after a perturbation in this equilibrium situation has been switched on. The model introduces an explicit time-dependent treatment of the polarization by means of the linear-response theory.

Radiative and nonradiative decay rates of a molecule close to a metal particle of complex shape.

We present a model to evaluate the radiative and nonradiative lifetimes of electronic excited states of a molecule close to a metal particle of complex shape and, possibly, in the presence of a solvent. The molecule is treated quantum mechanically at Hartree-Fock (HF) or density-functional theory (DFT) level. The metal/solvent is considered as a continuous body, characterized by its frequency dependent local dielectric constant.

A polarizable continuum model for molecules at diffuse interfaces.

In this work we illustrate an extension of the polarizable continuum model to describe solvation effects on molecules at the interface between two fluid phases (liquid/liquid, liquid/vapor). This extension goes beyond the naive picture of the interface as a plane dividing two distinct dielectrics, commonly employed in continuum models. The main feature of the model is the use of a diffuse interface with an electric permittivity depending on the position.

Excitation energy transfer (EET) between molecules in condensed matter: a novel application of the polarizable continuum model (PCM).

We present a quantum-mechanical theory to study excitation energy transfers between molecular systems in solution. The model is developed within the time-dependent (TD) density-functional theory and the solvent effects are introduced in terms of the polarizable continuum model (PCM). Unique characteristic of this model is that both "reaction field" and screening effects are included in a coherent and self-consistent way.

New developments in the symmetry-adapted algorithm of the Polarizable Continuum Model.

We present recent developments in the symmetry implementation of the Polarizable Continuum Model (PCM). The structure of the matrix, which defines the PCM solvent response, is examined, and we demonstrate how this matrix can be transformed to a block diagonal form where each block belongs to different irreducible representations of the molecular point group. This development is especially important at the Multi-configurational Self-Consistent Field (MCSCF) level where symmetry is needed to avoid problems with symmetry breaking in the wave function and facilitate the optimization of electronic excited states.