Towards an accurate determination of molar absorptivities in condensed phases: A computational approach based on multiconfigurational quantum chemistry and conformational sampling of the chromophore-environment complex
Ana Borrego-Sánchez,*a Madjid Zemmouche,b Isabelle Navizet,b Ignacio Sainz-Díaz,a Daniel Roca-Sanjuán*c
a) Instituto Andaluz de Ciencias de la Tierra (CSIC-University of Granada), Av. de las Palmeras 4, 18100 Granada, Spain.
b) Laboratoire Modélisation et Simulation Multi Échelle, Université Paris-Est, MSME UMR 8208 CNRS, UPEM, 5 bd Descartes, 77454 Marne-la-Vallée, France
c) Institut de Ciència Molecular, Universitat de València, Catedrático José Beltrán Martínez 2, 46980 Paterna, Spain.
In materials and biological systems, chromophores are confined to distinct types of chemical and physical environments, for instance, water solution, inside a pore, at the interlayer space of layered materials, etc. Interaction between the chromophores and light might be affected by the environment giving rise to changes with respect to the behavior of the isolated system. By using computational chemistry, a semiquantitative description of the physicochemical effects of light-matter interaction can be already obtained by studies with the isolated molecule. Nevertheless, to improve such description and provide a more realistic description, the environment must be considered. In this work, we shall focus on the determination of molar absorptivities (or molar extinction coefficients, e) of chromophores in condensed phases. For an accurate prediction of e two requirements are needed: (i) an accurate methodology for describing correctly both the ground and the distinct types of excited electronic states and (ii) a computational approach to sample the conformational space of the chromophore-environment complex. Regarding the first point, multiconfigurational quantum chemistry (mainly based on the complete-active-space second-order perturbation theory (CASPT2) method) is a practical tool here, much more robust than time-dependent density functional theory (TDDFT). For the conformational sampling, distinct approaches are available: (i) molecular (classical) dynamics, (ii) semiclassical dynamics or (iii) Wigner sampling. We shall compare in this contribution the performance of the three sampling strategies used with the CASPT2 method to determine the e of a model organic molecule, acrolein, in water solution and at the gas phase – water interface .
 A. Borrego-Sánchez, M. Zemmouche, I. Navizet, I. Sainz-Díaz, D. Roca-Sanjuán, in preparation