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Défense de thèse de doctorat en Sciences chimiques - Pierre BEAUJEAN

Quantum Chemistry Investigations on Nonlinear Optical Materials: from Reference to Complex Systems

Catégorie : défense de thèse
Date : 07/10/2021 15:00 - 07/10/2021 18:00
Lieu : PA02
Orateur(s) : Pierre BEAUJEAN
Organisateur(s) : Benoît CHAMPAGNE


  • Prof. Olivier DEPARIS (Département de Physique, UNamur), président
  • Prof. Benoît CHAMPAGNE (Département de Chimie, UNamur), secrétaire
  • Prof. Frédéric CASTET (Institut des Sciences Moléculaires, Université de Bordeaux)
  • Dr Marc de WERGIFOSSE (Institut für Physikalische und Theoretische Chemie, Universität Bonn)
  • Prof. Vincent LIÉGEOIS (Département de Chimie, UNamur)
  • Prof. Lionel SANGUINET (Laboratoire MOLTECH Anjou, Université d’Angers)
  • Prof. Daniel P. VERCAUTEREN (Département de Chimie, UNamur)


The interplay between light and matter gives rise to several phenomena, including nonlinear optical (NLO) effects. This thesis aims at describing and understanding, using quantum chemistry, the NLO properties of molecules. In particular, it focuses on their second (SHS) and third (THS) harmonic scattering responses: βSHS and γTHS, respectively. The goal is to provide insights and to help towards the design of new materials, in a multidisciplinary framework combining theory and experiment. In the first part, the chapters are dedicated to the accurate description of (gas phase) molecular responses of reference molecules, crucial for experimental measurements. So, a hierarchy of Coupled Cluster methods has been employed with large basis sets and checked against experimental results in order to select an appropriate level of approximation. Then, the first quantum chemical investigation on γTHS is reported, presenting the calculated values and their decomposition into spherical components, at the light of comparisons with βSHS. It shows that γTHS is dominated by its isotropic contribution contrary to βSHS, of which the major contribution is dipolar or octupolar as a function of the molecular structure. Finally, the impact of vibrational contributions has been addressed for the water molecule as a model system, thanks to a homemade implementation of finite-field differentiation techniques. It is shown that the contributions to the dynamic NLO properties are small but non-negligible (10% or less), while much larger in the static limit. The second part focuses on the study of molecules of increasing complexity, displaying large or remarkable second-order NLO responses. On the one hand, NLO switches have been explored, with a focus on the characterization (structures, linear and nonlinear optical responses) of each of their states as well as the βSHS contrast between them. In particular, two types of compounds have been considered: i) octupolar molecules with 6 ruthenium(II) centers that can be oxidized and ii) multi-state compounds, involving two or three benzazolooxazolidine units, leading up to 4 or 8 different states, respectively. In both cases, quantum chemical calculations have provided precious insights for a better understanding of their behavior and optimization. In particular, the second-order NLO responses have been rationalized using different few-state models to account for their complex architectures. On the other hand, a new methodology to study the NLO response of fluorescent proteins, biotags of interest in second-harmonic imaging microscopy, has been developed. As a proof of concept, two proteins have been considered, with promising results. For instance, for the bacteriorhodopsin, the comparison with experimental data is excellent, providing an avenue for unraveling the origin of these NLO responses.

These different contributions pinpoint the importance of quantum chemistry to deduce structure-activity relationships and help the design of new and improved molecules.


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