Ferric ferrocyanide (Prussian blue) and its analogues are renowned for the variety of properties and applications associated with them. At the same time, however, they suffer from issues related to their variable composition and poor crystallinity. As a result, we are preparing discrete cyanide-bridged clusters both to mimic these materials and to search for properties unique to the molecule, such as single molecule magnetism. The work in this dissertation has focused on the expansion of series of trigonal bipyramidal (TBP) cyanide-bridged clusters, [M(tmphen)2]3[M′(CN)6]2, that exhibit a variety of properties including spin crossover, charge-transfer-induced spin transition, and photomagnetism. One goal of the work was focused on the preparation of new paramagnetic TBP clusters incorporating various 3d metal ion combinations. Nine new clusters were prepared and characterized, including several “model compounds” with only one type of paramagnetic metal ion. The magnetic properties of these model compounds were combined to better explain the coupling through the cyanide ligands in clusters with two paramagnetic metal centers. An additional two clusters were also prepared that were found to exhibit a thermally induced LS Fe^II -> HS Fe^II transition. The spin crossover event was confirmed by magnetic susceptibility and Mössbauer spectroscopy, and variable temperature X-ray crystallography revealed the transitions to be distinct for each FeII center and dependant on the interstitial solvent. Another major goal of the work was to investigate the TBP clusters for their potential to be used as building-blocks to prepare 1-D extended structures of linked clusters, such as a {[Co(tmphen)2]3[Fe(CN)6]2[Mn(MeOH)4]}∞(ClO4)3 chain. A final research goal was a search for photomagnetic behavior, the change in magnetic properties with irradiation, related to spin transitions in several key TBP clusters. The Fe3Fe2 and Fe3Co2 TBP clusters were found to exhibit a light-induced excited spin state trapping (the LIESST effect) similar to that observed in mononuclear FeII compounds, and the photo-induced charge transfer that has been observed in Co-Fe Prussian blue materials is mimicked by the Co3Fe2 TBP molecular analogue.

Le développement de méthodes rapides, précises et ultra-sensibles pour la détection d'analytes cibles en solution est crucial pour la recherche et les applications potentielles en médecine ou biologie moléculaire. Une approche très prometteuse consiste à développer des nano-capteurs à partir de nano-objets métalliques (NOM) qui présentent une résonance d'extinction dans leur réponse optique. Cette résonance nommée résonance de plasmon de surface localisée (RPSL) peut être ajustée spectralement en jouant sur la nature, la morphologie et l'environnement du NOM. Mesurer des modifications sur la RPSL de nano-objets individuels en présence d'analytes cibles doit permettre de s'affranchir des effets de moyennes dans les mesures d'ensemble. De plus, cela ouvre la voie vers le développement d'échantillons micrométriques pour des tests multicibles sans étiquette (« label-free »).Dans ce travail on a développé un nouveau dispositif expérimental basé sur la technique de spectroscopie à modulation spatiale (SMS) permettant de sonder la réponse optique de NOM individuels en milieu liquide. En parallèle des méthodes de synthèse ont été mises au point pour obtenir des échantillons sondes stables permettant des mesures sur NOM unique, en particulier sur des bipyramides d'or qui présentent de nombreuses qualités intrinsèques faisant d'elles de bonnes candidates pour le « bio-sensing ».Des mesures ont été réalisées dans des environnements d'indice variable et les changements détectés sont en bon accord avec les simulations théoriques. De plus, de nombreuses études ont été réalisées pour comprendre l'influence des nombreux paramètres agissant sur la réponse optique des systèmes étudiés / Advances in the development of rapid, accurate and highly sensitive methods for detecting target analytes in solution will provide crucial tools for research and applications in medicine and molecular biology. One of the currently most promising approaches is the development of nanosensors based on the localized surface plasmon resonance (LSPR) of noble metal nano-objects (MNOs), which is an optical response that depends on their size, shape, composition and local environment. The ability to measure the modification of the reponse of a single MNO in the presence of a target analyte would allow each object to act as an independent probe with increased sensitivity as the signal would be isolated from the averaging effects of ensemble measurements. Furthermore it would allow the development of micrometric, functionalized multiprobe samples for multitarget label-free assays.In this work, a novel experimental setup based on the spatial modulation spectroscopy (SMS) technique has been developed to measure the optical response of individual nano-objects in a liquid environment. In parallel, a new technique has also been developed to elaborate stable probes for measurements with the new setup, with a focus on gold bipyramids due to numerous qualities that make them excellent candidates for biosensing probes. The setup has been used to measure the response of individual objects in environments of different real refractive indices and the detected changes have been shown to be in good agreement with theoretical calculations. Numerical studies have also been performed to investigate the influence on the optical response of numerous factors encountered in the studied systems