PhD defense: Julien Malletroit

Title

Investigation of negative photochromic molecules, towards optically active materials

Abstract

Photochromic molecules can change color under light irradiation, making them interesting for many industrial applications. This thesis aims to identify and study negative photochromic compounds to incorporate them into a textile using a polymer matrix. After a rigorous bibliographical study, the family of Stenhouse donor-acceptor adducts (DASA) was identified as a good candidate for this application. Initially colored, they become colorless under irradiation in the visible by isomerization, changing the molecule from a linear to a cyclic form. Based on precise specifications, a selection was made to identify the DASA with properties closest to the target objective. A complete spectroscopic study (steady-state and photokinetic) of the properties of the DASA in solution was carried out to quantify, for the first time, the various photophysical parameters such as the molar absorption coefficients, the photochromic quantum yields and the rate constants of the associated reactions. The intermediate species' critical role in determining photoisomerization's overall kinetics was studied and characterized, revealing dual kinetics for the photochromic response. The reaction is initially photo-activated, followed by a thermally controlled phase. Experiments at different temperatures and irradiation powers demonstrated this dual kinetics. These studies were also carried out in a polymer matrix to create functional surfaces, revealing different behaviors compared with the solution. Using a source mimicking the solar spectrum instead of a monochromatic light confirmed the use of DASA to develop new innovative photochromic materials.

 

PhD supervision

• Director: Rémi Métivier - Research Director, CNRS - ENS Paris-Saclay
• Co-director: Guillaume Laurent - Scientist, CNRS - ENS Paris-Saclay

Members of the jury

• Pascale Changenet, Research Director (LOB, Ecole Polytechnique)

• Emilie Génin, Professor (ISM, Université de Bordeaux)

• Pierre Mialane, Professor (ILV, Université de Versailles Saint Quentin en Yvelines)

• Guy Royal, Professor (EDYTEM, Université Savoie Mont-Blanc)

• Sarah Berhanu (DGA technical expert)

• Rachid Jaoui (invited)