ED Sciences Chimiques
Brønsted acid-catalyzed hydroarylation of alkynes: metal-free route towards arylidene-vinylidene polymers for optoelectronics and photocatalysis
by Luca CAPONECCHIA (Laboratoire de Chimie des Polymères Organiques)
The defense will take place at 9h30 - Salle de conférence 3e étage Institut des Sciences Moléculaires (ISM), Bâtiment A12, 351 Cours de la Libération, 33405, TALENCE cedex
in front of the jury composed of
- Cyril BROCHON - Professeur - Université de Bordeaux - Directeur de these
- Christine LARTIGAU-DAGRON - Maîtresse de conférences - Université de Pau et des Pays de l'Adour - Rapporteur
- Patrick Yves TOULLEC - Professeur - Université de Bordeaux - CoDirecteur de these
- Virginie MOURIèS-MANSUY - Professeure - Sorbonne Université - Rapporteur
- Claudia BIZZARRI - Associate Professor - Università degli studi di Roma Tor Vergata - Examinateur
- Dario BASSANI - Directeur de recherche - Université de Bordeaux - Examinateur
This manuscript presents the development of a metal-free route to conjugated polymers based on Brønsted acid-catalyzed hydroarylation of alkynes, with the goal of creating new organic semiconductors for optoelectronic and photocatalytic applications. The work begins with the synthesis of suitable monomers and model molecules, which were used to validate the viability of the method and to understand how reaction conditions influence conversion, selectivity, and product formation. These early studies showed that the use of directing groups on the alkyne can lead to an activation of the alkyne and effectively increase the reactivity, the regio- and diasteroselectivity. The reaction was also found to be highly sensitive to acid strength, solvent, concentration, and monomer structure. The application of this methodology to the synthesis of conducting polymers was successfully accomplished using diynes and aromatic nucleophiles bearing two active sites. The first polymers obtained showed only moderate molecular weights and relatively broad dispersities, indicating that chain growth was not yet fully controlled. Further optimization demonstrated that concentration had the strongest effect on molecular weight and dispersity. Overall, these results proved the feasibility of the reaction while highlighting the need for improved control of the reaction conditions to obtain better-defined polymers. A major conclusion of the thesis is that the optoelectronic properties of these materials are governed not only by chain length, but above all by backbone conformation and steric effects. Density functional theory calculations supported this interpretation by revealing that steric hindrance on the arylidene-vinylidene backbone prevented conjugation and reduced electronic delocalization. The polymers displayed frontier orbital energies consistent with a p-type semiconducting behaviour, making them promising candidates for further materials development. The thesis then explored structural modification as a way to tune polymers properties and performance. The introduction of electron-withdrawing groups into the conjugated backbone resulted in the effective lowering of the band gap and shifting absorption and emission toward the visible region. Donor-acceptor design emerged as a particularly powerful strategy, enabling a better balance between optical absorption, emission, and redox properties. However, the work also showed that not all substitutions behave as expected, since some modified monomers led to no or unexpected reactivity during polymerization. This underlined the importance of combining careful control of chemical reactivity with electronic tuning. Post-polymerization modification was also investigated through photocyclization, with the aim of increasing rigidity and planarity to improve conjugation. While this transformation worked well on model dimers, it failed on the polymers probably because steric congestion prevented the necessary conformational rearrangement. This result reinforced the central message of the thesis: the design of the monomer framework is decisive, and successful materials development depends on achieving an efficient conjugation during the synthesis or post-modification. Finally, the synthesized polymers were evaluated as photocatalysts for the degradation of methylene blue in water under visible light. Several materials showed promising activity, and the results demonstrated that morphology strongly affects performance. The study also suggested that trace impurities could influence the apparent photocatalytic efficiency, emphasizing the need for rigorous characterization. In conclusion, this thesis establishes a coherent relationship between synthesis, structure, and function for a new family of conjugated polymers, and provides a solid foundation for future development of sustainable materials for organic electronics and photocatalysis.