Le mercredi 1^er juillet 2026, Valentin FOIDART présentera l'examen en vue de l’obtention du grade académique de Docteur en Sciences (Collège de doctorat en Chimie) sous la direction d'Anne-Sophie DUWEZ.

Cette épreuve consistera en la défense publique d’une dissertation intitulée :

« Synthesis and Mechanical Investigations of Triazolinedione-based Click-Chemistry Adducts by Single-Molecule Force Spectroscopy ».

Le Jury sera composé de :

Mme C. JEROME (Présidente), Mmes et MM. S. CUENOT (Université de Nantes), A.-S. DUWEZ (Promotrice), A. MESCOLA (Istituto Nanoscienze Modena), A. MURMILIUK, R. RIVA (Secrétaire).

Abstract

When we pull on a material, we rarely picture the applied force triggering a precise chemical reaction deep within its molecules. This is exactly the principle behind mechanochemistry, and more specifically behind mechanophores: small molecular units designed to transform or break under mechanical stress. Embedded in a polymer, they open the way to materials that can change colour under strain, heal themselves, or release an active molecule on demand.

This thesis focuses on a particularly promising family of chemical bonds, formed through "click" chemistry from triazolinediones (TAD). These bonds have the advantage of forming very rapidly at room temperature, and of being able to come apart in a controlled way depending on the chemical partner chosen (anthracene, indole or citronellol). While their sensitivity to heat is well documented, their behaviour under a mechanical force remained largely unexplored, because earlier studies relied only on ensemble techniques and provided no information at the single-molecule scale.

To observe a single bond at a time, this work relies on single-molecule force spectroscopy by atomic force microscopy (AFM-SMFS), which stretches a polymer chain between a tip and a surface and measures the force needed to break it. A substantial part of the thesis therefore consisted in synthesising tailor-made, clean and well-defined polymers, equipped with anchoring points strong enough to withstand stretching until the mechanophore itself ruptures.

The experiments show that isolating the rupture signature of the mechanophore alone is a considerable challenge. By strengthening the anchoring strategy, rupture events at relatively higher forces (around 600 piconewtons) could be recorded, yet the target signal remained difficult to separate from non-specific interactions. Theoretical simulations suggest that the surrounding environment (the solvent) and the pulling orientation strongly lower the expected rupture force. Although this signature could not be fully isolated, the thesis identifies the key parameters governing this type of measurement and outlines concrete directions for future work.

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