Polarizable continuum model chromophores

Organometallic systems such as porphyrines have been investigated because of the possibility to fine tune their response by functionalization[105-107]. Systems of increased the dimensionality have been of particular interest [108-111], Concomitant to the large effort to establish useful structure-to-properties relationships, considerable effort has now been put to investigate the environmental effects on TPA[112-114], For example, the solvent effect has been studied for a small linear push-pull chromophore using a self-consistent reaction field (homogeneous solvation) method employing a spherical cavity and an internal force field (IFF) method[l 12] in another study the polarizable continuum model has been employed to calculate the relevant quantities to obtain the TPA cross-section in the limit of a two-state model[113] Woo et al. made a critical study of experimental comparison of TPA cross-sections in different solvents[114]. 

Abstract The computational study of excited states of molecular systems in the condensed phase implies additional complications with respect to analogous studies on isolated molecules. Some of them can be faced by a computational modeling based on a continuum (i.e., implicit) description of the solvent. Among this class of methods, the polarizable continuum model (PCM) has widely been used in its basic formulation to study ground state properties of molecular solutes. The consideration of molecular properties of excited states has led to the elaboration of numerous additional features not present in the PCM basic version. Nonequilibrium effects, state-specific versus linear response quantum mechanical description, analytical gradients, and electronic coupling between solvated chromophores are reviewed in the present contribution. The presentation of some selected computational results shows the potentialities of the approach. 

Mennucd B, Cappelli C, Guido CA, Cammi R, Tomasi J. Stmctures and properties of electronically excited chromophores in solution from the polarizable continuum model coupled to the time-dependent density functional theory.JPhys Chem A. 2009 113(13) 3009-3020. http //dx.doi.org/10.1021/jp8094853. 

Vukovic, S., Corni, S., and Mennucci, B. (2009] Fluorescence enhancement of chromophores close to metal nanoparticles. Optimal setup revealed by the polarizable continuum model, J. Phys. Chem. C, 113, 121-133. 

We have reviewed some recent computational methodologies based on the combination of the TDDFT theory with the Polarizable Continuum solvation Model (PCM) to study chromophores in homogenous solutions. In particular we have considered... 

Since pNA and most of the chromophores of interest have large dipole moments an important feature of the continuum models is the introduction of the reaction field. The pNA molecule at the centre of the cavity in the continuum induces a polarization on the surface of the cavity, which produces the reaction field acting on the central molecule. This reaction field changes the dipole moment of the pNA molecule via the linear polarizability. A self consistent procedure is required in which the effects of the reaction field and also the effects of the applied macroscopic fields modified by the internal field factors are included in a self-consistent determination of the molecular response within a specified quantum mechanical model. 

To begin to elucidate such issues and to create a theoretical framework for them, we have focused [4-9] on a model of a protonated Schiff base (PSB) in a nonequilibrium dielectric continuum solvent. A key feature for the Sj-Sq Cl in PSBs such as retinal which plays a key role in the chromophore s cis-trans isomerization is that a charge transfer is involved, implying a strong electrostatic coupling to a polar and polarizable environment. In particular, there is translocation of a positive charge [92], discussed further below. Charge transfer also characterizes the earliest events in the photoactive yellow protein photocycle, for example [93],... 

The chromophore has been treated at the Hartree-Fock or density functional theory level (see Chapter 4), in the determination of both its ground state and its properties. This model for the molecule represents a remarkable progress in the accuracy of the description of the molecular chromophore compared to polarizable point dipole model. The solvation effects have been described with the PCM. More in details, the solvent is described as a continuum dielectric which occupies all the space free from the metal specimen and the molecule is hosted in a molecular shaped cavity inside such dielectric. 

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