Titre de la dissertation: Study of the Photophysical and Photochemical Properties of Heteroleptic Diimine-Diphosphine Copper(I) Photosensitizers

Promoteurs de thèse: Monsieur Jérôme Cornil et Madame Cécile Moucheron

Résumé de la dissertation: The idea of ​​building a world based on sunlight as the main source of energy is not new. Indeed, a hundred years ago, Giacomo Ciamician, an Italian chemist, advocated separating from fossil fuels to use the virtually infinite source that is our sun (Science. 1912, 36, 385–394). At the time he only referred to coal and, no mention of climate change was present in his development. However, recent geopolitical tensions and extreme weather events mean that the idea of ​​parting away from fossil fuels is very topical.Inspired by natural photosynthesis, artificial systems able of converting solar energy into chemical energy were developed as early as the end of the 1970s (which coincides with the oil crisis). These systems use three essential components, each of which plays a specific role. Two catalysts are needed, one to oxidize water to dioxygen and one to reduce protons to dihydrogen or reduce carbon dioxide to different forms. The third component is a photosensitizer. Its role is to absorb sunlight to enter an excited state. The energy accumulated by the excited state is then used to trigger a chain of electron transfers from water to protons or CO2 through the various components.Historically, the most effective photosensitizers are complexes of noble transition metals such as ruthenium, iridium or rhenium, the emblematic example of which is the [Ru(bpy)₃]²⁺ complex. Although these complexes are very effective, the fact that they are based on noble metals, and therefore scarce, is a major limitation for their use on a global scale. Developing photosensitizers based on more abundant transition metals such as iron, cobalt or nickel is therefore a crucial step. Unfortunately, such complexes do not have the necessary properties for this type of application. This is especially true for their extremely short excited state lifetimes which prevent them from performing the desired reactions.Copper is an exception for these abundant metal complexes. Indeed, since the 1980s, copper(I) complexes have been known to be luminescent and have sufficient excited state lifetimes to induce photochemical reactions. These tetrahedral complexes are composed of a central copper(I) atom with two identical diimine ligands chelated to it. Although these complexes have been widely studied, they not often found in artificial photosynthetic systems. This is not the case with heteroleptic copper(I) complexes which, over the past ten years, have shown their ability to compete with photosensitizers based on noble metals for this type of application. These heteroleptic copper(I) complexes, composed of a diimine ligand and a diphosphine ligand, are the focus of this work.This thesis was carried out under a joint supervision. It combines the expertise of two laboratories, that of the Chimie Organique et Photochimie (COP) at the ULB and that for Chemistry of Novel Materials (CMN) at the UMons. The COP has a rich history in the study of photoactive ruthenium(II) complexes and has particular expertise in the design of diimine ligands with a pronounced p-acceptor character. The CMN has expertise in modeling the electronic and optical properties of organic semiconductor molecules.The work presented in this manuscript therefore aims at the experimental and theoretical study of heteroleptic copper(I) complexes carrying diimine ligands with a strong p-acceptor character. These complexes are designed with the aim to improve their properties for their use as photosensitizer in artificial photosynthetic system.