Grand Séminaire d'Institut

Vendredi 18 Décembre 2020 à 11h00.

Electronic structure and relaxation of solvated molecules studied by time-resolved photoelectron spectroscopy

''Electronic relaxation of molecular chromophores upon photoexcitation plays an important role in many biological processes, such as vision, photosynthesis and stability of DNA against the sunlight. Many experimental and theoretical studies have been conducted to unravel these dynamics, which often involve fast passages through conical intersections. These studies are complicated by the fact that most chromophores of biological importance are rather large molecules and strongly affected by environment, either solvent or a protein cage. Thus, experimental approaches are necessary, which can deliver direct and analytical information for the state-of-the-art first-principles methods. Photoelectron spectroscopy has traditionally been one of the most direct methods to analyze electronic structure. Recently, we extended the method of XUV time-resolved photoelectron spectroscopy to solvated organic molecules [1]. We employed an HHG source for production of femtosecond XUV pulses and combined it with the microliquid jet technology. Here we apply this method to look at the relaxation dynamics of several organic dyes.
In particular, we study relaxtion of Methyl Orange and Metanil Yellow, two aminoazobenzenes, solvated in water. Typical for azobenzenes, these molecules undergo ultrafast relaxation via conical intersections, which may involve cis-trans-isomerization. We complement experimental data with a surface hopping TDDFT calculations [2] employing B3LYP+D3 and ωB97X-D functionals and demonstrate that the method is suitable for description of these ultrafast dynamics and can recover absolute binding energies observed in the experiment. Our results pave the way towards quantitative understanding of evolving electronic structure in photoinduced relaxation processes.
[1] J. Hummert et al, J. Phys. Chem. Lett. 9, 6649 (2018)
[2] M. Wolhgemut, J. Chem. Phys. 135, 054105 (2011); A. Homeniuk, J. Chem. Phys. 139, 134104 (2013)
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