In molecular magnetism, rational design and serendipity have played complementary roles in the synthesis of complexes which display a breadth of interesting physical characteristics. These range from the basic understanding of magneto‐structural correlations, to more complicated phenomena such as slow relaxation of the magnetisation, spin frustration effects, and tuning magnetic interactions with a view to spintronics. The inherent physical properties of these complexes has already afforded molecules which can behave as single‐molecule magnets, singlechain magnets, single‐ion magnets, magnetic metal‐organic frameworks, magnetic refrigerants, and molecular qubits. Even when the building blocks are well known, the rational design of magnetic clusters can be extremely difficult, with the shape and nuclearity often dominated by several internal and external factors. Metallosupramolecular processes proffer an attractive strategy to the rational design of these clusters by making use of structurally‐rigid precursors which, when combined in the correct stoichiometric ratio, can be used to construct various predefined discrete two‐ and three‐dimensional polygons and polyhedra. In particular, the use of metalloligands as structurally‐rigid precursors is appealing, not only because of their often‐straightforward synthesis, but because of their ability to be easily modified in order to create comparable building blocks with different chemical and physical properties. It is therefore surprising that there are limited examples of magnetic architectures built through this approach. Each chapter of this thesis aims to exploit the use of acetylacetonate‐based paramagnetic metalloligands for the synthesis of structurally analogous magnetic coordination capsules, with inherently different magnetic properties. Chapter 2 describes the structural and magnetic studies of fourteen tetradecanuclear coordination cubes, synthesised using the paramagnetic metalloligand [MIIIL3] (MIII = Cr, Fe; HL = 1‐(4‐pyridyl)butane‐1,3‐dione). The heterometallic [MIII8MII6L24]n+ (MII = Co, Ni, Cu, and Pd; n = 0‐ 12) cubes formed from the reaction of [MIIIL3] and a “naked” MII salt are all topologically similar, with the MIII ions occupying the corners of the cubes and the MII ions occupying the faces. Excluding the PdII‐based cube, all of the complexes display magnetic exchange interactions at low temperatures. Due to the enormous size of these clusters and their resulting matrices, the magnetic fitting was done using the process of statistical spectroscopy. Chapter 3 describes the structural and magnetic studies of five [MIII2MII3L6]n+ (MIII = Cr, Fe, and Al; MII = Co, Zn, and Pd; HL = 1‐(4‐pyridyl)butane‐1,3‐dione; n = 0‐6) trigonal bipyramids, built using the diamagnetic and paramagnetic metalloligands [MIIIL3]. [FeIII2CoII3L6Cl6] represents the first magnetic trigonal bipyramid synthesised through the pyridyl‐based metalloligand approach. SQUID magnetometry studies show a weak antiferromagnetic exchange interactions between the FeIII and CoII ions, while EPR spectroscopy measurements demonstrate a small increase in the zero‐field splitting parameter of the FeIII ion upon coordination of [FeIIIL3] to a MII ion. Complete active space self‐consistent field (CASSCF) calculations show the axial zero‐field splitting parameter of CoII to be ≈‐14 cm‐1, which is consistent with the magnetothermal and spectroscopic data. Chapter 4 describes the synthesis and characterisation of six magnetic trigonal bipyramids, synthesised through dynamic covalent reactions of the metalloligand [FeIIILNH23] (HLNH2 = 1‐(4‐ aminophenyl)butane‐1,3‐dione) with either a dialdehyde or diacyl dichloride. The three [FeIII2MII3Lim3]n+ (MII = Co, Ni; n = 0‐6) imine‐based cages are formed from the reaction of the metalloligand with 2,6‐pyridinedicarboxaldehyde in the presence of a templating MII salt and a catalytic amount of acid, whereas the three [FeIII2Lam3] amide‐based cages are formed from the reaction of the metalloligand with isophthaloyl chloride in the presence of a base. The [FeIII2NiII3Lim3]n+ trigonal bipyramid displays weak antiferromagnetic interactions between FeIII and NiII ions, with JFe‐Ni = ‐0.12 cm‐1 and DNi = 8.93 cm‐1, while the [FeIII2Lam3] amide‐based cages display interesting configurational features dominated by the enthalpic gain from a series of intermolecular interactions.

La réponse optique de nano-objets métalliques et semi-conducteurs a été étudiée par spectroscopie par modulation spatiale (SMS), une technique permettant de détecter des nano-objets individuels et d'en mesurer quantitativement la section efficace d'extinction. Dans le cadre de ce travail, nous avons systématiquement corrélé ces mesures optiques à une caractérisation bi- voire tridimensionnelle de leur morphologie, permettant une comparaison précise des mesures avec des simulations numériques. Le premier volet de cette thèse décrit une étude détaillée de l'effet de la déposition de nano-objets métalliques de forme allongée (nanobâtonnets et nanobipyramides) sur un substrat absorbant. Nos expériences montrent qu'elle conduit à un élargissement de la résonance plasmon de surface, dont l'ampleur dépend fortement de la forme et de l'encapsulation des nano objets. En combinant la SMS avec une approche pompe-sonde, nous avons pu mesurer la réponse ultrarapide de nano-bipyramides d'or individuelles, qui contient une contribution de plusieurs de leurs modes de vibration, permettant d'accéder à leur fréquence et taux d'amortissement, en s’attachant en particulier à l'effet d'une encapsulation diélectrique des bipyramides. Au cours de cette thèse, nous avons étendu l'application de la SMS à des nano-objets très allongés avec une dimension micrométrique (nanofils et nanopointes), dans le but notamment d'étudier leur réponse optique, leur interaction avec une nanoparticule d’or et d’obtenir des informations sur leur profil d'absorption, une information essentielle pour l'interprétation d'expériences d'émission électronique (effet de champ) ou ionique (tomographie de sonde atomique) / The optical response of metallic and semi-conductor nano-objects has been studied by spatial modulation spectroscopy (SMS), a technique allowing to detect single nano-objects and to quantitatively measure their extinction cross-sections. During my thesis, we have systematically correlated these optical measurements with the 2D or 3D characterization of their morphology, allowing a precise comparison of the measurements with numerical simulations. The first part of my PhD thesis describes a detailed study of the effect of the deposition of elongated nano-objects on an absorbing substrate. Our experiments show a spectral broadening of the surface plasmon resonance, whose extent highly depends on the shape and the encapsulation of the nano-objects. By combining SMS with a pump-probe approach, we were able to measure the ultrafast response of single gold nano-bipyramids. This response contains a contribution from several vibration modes, allowing extraction of their frequencies and damping times. In particular, we have addressed the effect of a dielectric encapsulation of bipyramids on their vibrational quality factors. During this thesis, we extended the use of SMS to very elongated nano-objects with a micrometric dimension (nanowires and nanotips), with the goal of studying their optical response, their interaction with a gold nanosphere and obtaining information on their absorption profile, as required to interpret electronic (field effect) or ionic (atom-probe tomography) emission experiments

Les nanoparticules d’or (AuNPs) intriguent tout particulièrement ces dernières années de par leurs propriétés fascinantes. Elles sont variables selon la forme et la taille des nanoparticules ce qui en fait des objets ouvrant des perspectives dans plusieurs domaines. L’or est d’autant plus intéressant qu’il a une grande flexibilité de ces bandes de résonance plasmon de surface, allant du visible au proche infrarouge (IR). Au cours de cette thèse, nous avons donc travaillé sur la synthèse d’AuNPs de tailles et de formes différentes pour pouvoir travailler à de nombreuses longueurs d’onde du visible à l’IR. Cette multitude de AuNPs nous a permis d’étudier l’effet de ces différentes résonances plasmons sur des chromophores afin d’essayer de comprendre les mécanismes de ces interactions. Le but final de ces travaux, outre l’amélioration de la compréhension de ces interactions, est la réalisation de matériaux monolithiques pour l’optique par une approche sol-gel permettant l’incorporation de molécules optiquement actives et de ces systèmes plasmoniques, qui donnent des propriétés intéressantes aux matériaux obtenus. Nous nous sommes intéressés plus précisément aux propriétés d’absorption non-linéaire, dans le but de réaliser des matériaux limiteurs optiques pour protéger des systèmes optiques contre des rayonnements intenses, comme les lasers. Ces systèmes ont commencé à être mis au point dans les thèses précédentes faites au laboratoire mais la compréhension amenée par ces travaux auront permis d’approfondir les interactions particules-chromophores et le rôle de la longueur d’onde de la résonance plasmon afin d’optimiser l’efficacité en limitation optique. / Gold nanoparticles (AuNPs) particularly intrigued over the last decades because of their fascinating properties. They vary according to the size and shape of nanoparticles making objects opening opportunities in many areas. Gold is especially interesting since it has a great flexibility of these resonance surface plasmon bands ranging from the visible to near infrared (IR).In this thesis, we worked on the synthesis of AuNPs of different sizes and shapes in order to be able to work in many wavelengths from visible to IR. This multitude of AuNPs enabled us to study the effect of these different plasmon resonances of chromophores in an effort to understand the mechanisms of these interactions. The ultimate goal of this work, in addition to improving the understanding of these interactions, is the realization of monolithic materials for optics by a sol-gel approach allowing the incorporation of optically active molecules and these plasmonic systems, which give interesting properties to the obtained materials. We focused specifically on nonlinear absorption properties, in order to produce optical limiting materials to protect optical systems against intense radiation, such as lasers.These systems began to be developed in previous PhD thesis made in our laboratory but the understanding brought by this work have helped deepen the particles-chromophore interactions and the role of the wavelength of the plasmon resonance in order to optimize efficiency in optical limiting.