Polarizable QM/Classical Approaches for the Modeling of Solvation Effects on UV–Vis and Fluorescence Spectra: An Integrated Strategy

Abstract

Hybrid methods combining quantum chemistry and classical models are largely used to describe solvent effects in absorption and emission processes of solvated chromophores. Here we compare three different formulations of these hybrid approaches, using a continuum, an atomistic, or a mixed description of the solvent. In all cases mutual polarization effects between the quantum and the classical subsystems are taken into account. As a molecular probe, 3-hydroxyflavone has been selected due to its rich photophysics, which involves different tautomeric and anionic forms. We show that a clear assignment of the measured spectroscopic signals to each specific form can be achieved by combining the different solvation models into an integrated and cost-effective strategy. Previously proposed mechanisms for the excited-state proton transfer (ESIPT), specific solvent perturbation effects on ESIPT, and solvent-assisted anion formation are also validated in terms of short- and long-range solvation effects.

An enhanced sampling QM/AMOEBA approach: The case of the excited state intramolecular proton transfer in solvated 3-hydroxyflavone

“…The selection of a long-range corrected functional in combination with a 6-31G(d, p) basis set has been based on tests presented in a previous paper of some of the authors on absorption and emission energies of 3HF. 57 As a further test on the reliability of the selected QM level, we performed a relaxed scan of the geometry along the reaction coordinate described below: our combination of the basis set and functional gave an excited state barrier of 0.9 kcal/mol for the isolated system, which is in line with the estimate obtained by taking into account a tunneling mechanism 0.6-2.5 kcal/mol. 58 Within the AMOEBA force field, the electrostatic and polarization interactions are represented in terms of a fixed multipolar expansion (up to quadrupoles) and an isotropic polarizability for the MM atoms.…”

“…As regards the computational works, most of them focused on the simulation of the spectroscopic properties of the N and T tautomers and the involved PES. 42,57,[67][68][69] An extensive investigation of the time-resolved process was, however, reported by Bellucci and Coker, using classical molecular dynamics in conjunction with empirical valence bond (EVB) potentials. 70 The goal of those simulations was the identification of the mechanisms responsible for both ultrafast transfer and slow proton transfer in different solvents.…”

Accounting for Vibronic Features through a Mixed Quantum-Classical Scheme: Structure, Dynamics, and Absorption Spectra of a Perylene Diimide Dye in Solution

“…In this way, the effect of the extension of the QM partition on the description of solvent shifts, 111 solvent broadening, 75 or other photochemical properties, 112 has been investigated. From the methodological point of view, beside the possibility of combining explicit and continuum models, 113 recent progresses have been made in the use of ab initio dynamics with non periodic boundary conditions, 114 polarizable force fields, 115,116 or clustering methods combined to the perturbation matrix method to recover the effect of local fluctuations of the environment. 51,52 Interestingly, most of the proposed compu-tational protocols are often indicated as MQC, with implicit reference to the description of the electrons, or more precisely, to whether solute/solvent interactions are computed according to quantum mechanics or with force fields.…”

CCSD‐PCM Excited State Energy Gradients with the Linear Response Singles Approximation to Study the Photochemistry of Molecules in Solution

“…While the development of methods to evaluate these energy gradients for isolated molecules is well established, for density functional theory (DFT) as well as wave function methods, the inclusion of solvation effects is still an active field of research. [1][2][3][4][5][6] Solvent effects on excited states are most efficiently introduced with implicit solvation models, such as the polarizable continuum model (PCM), [7,8] because the solvent reorganization around the solute charge density is implicitly included in the static or dynamic dielectric constant. Implicit models are particularly important for the evaluation of stationary points on the EE-PES, because the explicit solvation alternatives, i. e. geometry optimizations of multiple snapshots from ground state molecular dynamics (MD) or direct excited state MD simulations, are computationally prohibitive.…”