PhD defense: Léa Chocron

Title

Investigation of new photochromic molecules for solar energy storage and on demand release.

Abstract

In the context of the energy transition, harnessing solar energy represents a promising approach. However, due to its intermittent nature, the development of efficient storage solutions is essential to make it a credible alternative to traditional energy sources. In this context, MOST (Molecular Solar Thermal) systems use reversible photoisomerisable molecules, known as photochromes, to store solar energy in chemical form and release it on demand as heat. In this thesis, we explore acid sensitive photochromic molecules from the diarylethene (DAE) family in the framework of MOST applications. In particular, we show that these molecules can be converted under light irradiation into a higher energy isomer capable of storing energy over long periods; the addition of acid acts as a chemical trigger for the return to the initial form (thermal back reaction), thereby releasing the stored energy. Eight molecules exhibiting these features were studied by spectroscopy to quantify their absorption properties as well as the kinetics of the various processes; their energy storage capacities were also evaluated by differential scanning microcalorimetry and quantum chemical calculations, revealing a storage capacity on the order of 100 kJ/mol. Furthermore, we showed that small amounts of acid are sufficient to efficiently trigger the thermal back reaction of the molecules, and a kinetic model was developed to rationalise these experimental observations. Two molecules were then studied in a continuous flow device, featuring a charging reactor under irradiation and an activation reactor containing a fixed bed of acid to trigger the thermal back reaction. Finally, a DAE molecule was mixed with a photoacid both to facilitate visible light absorption and to control the back reaction by in situ acid release under light irradiation. Altogether, these studies highlight DAE molecules as highly promising candidates for MOST applications, particularly due to the use of acid as a chemical trigger for energy release.

PhD supervision

• Director: Dr Rémi Métivier, Research Director, CNRS - ENS Paris-Saclay
• Co-director: Pr Keitaro Nakatani, Professor, PPSM, ENS Paris-Saclay

Members of the jury

• Denis Frath, Chargé de recherche, Laboratoire de Chimie de l'ENS de Lyon, Ecole Normale Supérieure de Lyon, Rapporteur

• Kasper Moth-Poulsen, Professor, Polytechnic University of Barcelona, Rapporteur

• Damien Baigl, Professeur des universités, Pasteur, ENS Université PSL, Examinateur

• Lou Barreau, Maîtresse de conférences, ISMO, Université Paris-Saclay, Examinatrice

• Karine Loubière, Directrice de recherche, Laboratoire de Génie Chimique, INP Toulouse, Examinatrice

• Christophe Coudret, Directeur de recherche, Laboratoire Softmat , Université Toulouse, Examinateur

• Pei Yu, Chargé de recherche, ICMMO, Université Paris-Saclay, Invited