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Chiral nematic thin films containing responsive dopants have previously been considered as sensors and dosimeters. Some systems have been developed, with mixed results. The investigation so far has been piecemeal, with little attention paid towards understanding the properties that govern how these sensors operate. By carefully considering these properties, we believe that it is possible to predict the effectiveness of a sensor, and therefore a framework can be established which would allow only sensors with significant potential to be investigated. The applications of a variety of chiral nematic thin films incorporating responsive dopants is modelled and then investigated experimentally. The systems chosen for investigation were selected using the criteria of commercial potential and synthetic simplicity. In each case it was found that the behaviour of these systems could be predicted well from simple experimental data. The systems chosen for investigation were judged on the basis of two key criteria: They must be systems that deal with a target that is of commercial interest, so that performance expectations for 'real-life' applications can be given at the start of the research process. They must be manufactured only using materials and processes that are commercially available. These limitations were chosen to highlight the conditions under which such a model would be expected to operate. In this work, a successful model that predicts sensors behaviour from basic experimental information was developed and shown to match well with experimental results. In the process, three new sensing systems were developed, all with potential commercial significance. Additionally, some observations regarding the methods of operation which are most likely to result in high sensitivity and low cross-sensitivity have been made.

L'introduction d'atomes d'azote sur des squelettes organiques reste une étape clé pour la synthèse de molécules bioactives alcaloïdes. Depuis quelques années, l'insertion catalytique de nitrène sur les alcènes ou pour la fonctionnalisation des liaisons C-H est devenue un outil indéniable pour une telle introduction. Cependant, les systèmes catalytiques homogènes habituellement utilisés pour cette transformation présentent des inconvénients tels que la stabilité ou la séparation après réaction. Des catalyseurs supportés recyclables sont alors apparus comme une alternative intéressante pour surmonter ces problèmes. Dans le cadre de notre intérêt continu pour le développement de méthodologies durables, nous avons conçu de nouveaux catalyseurs valorisables efficaces, conformes aux principes de la chimie verte. Ici, la première insertion de nitrène pour l'aziridination en utilisant une nanoferrite chargée de cuivre réutilisable comme catalyseur sera présentée. Les propriétés magnétiques des nanoparticules permettent une récupération facile de ces catalyseurs avec un simple aimant externe. Nous montrerons que les catalyseurs peuvent être réutilisés 5 fois avec une conversion totale du styrène et de bons rendements, même après 5 essais. Les investigations après caractérisation complète ont montré une réduction de la charge de cuivre au fur et à mesure des cycles, ce qui peut être dû à un ancrage faible. Ce résultat nous incite à explorer différents linkers entre les nanoparticules magnétiques et le cuivre afin de diminuer cette lixiviation. Plusieurs lieurs présentant des fonctions différentes d'ancrage MNP et de chélation de Cu seront présentés. En outre, l'extrapolation réussie de cette méthodologie à des dérivés de styrène substitués pauvres en électrons ou riches en électrons sera démontrée, ainsi que l'aziridination d'oléfines à longue chaîne qui seront exposées / Introduction of nitrogen atoms onto organic skeletons remains a key step for the synthesis of alkaloid bioactive molecules. Since a few years, catalytic nitrene insertion on alkenes or for C-H bond functionalization has emerged as an undeniable tool for such introduction. However, homogeneous catalytic systems usually used for this transformation present some drawbacks such as stability, or separation after reaction. Recyclable supported catalysts have then arisen as a valuable alternative to overcome these issues.As part of our continued interest for the development of sustainable methodologies, we designed new and efficient recoverable catalysts fitting by the way the green chemistry principles. Here, the first nitrene insertion for aziridination using a reusable copper-loaded nanoferrite as catalyst will be presented. Magnetic properties of the nanoparticles allow an easy retrieval of those catalysts with a simple external magnet. We will show that the catalysts could be reused for 5 times with total conversion of styrene and good yields, even after 5 runs.Investigations after full characterization showed a reduction of copper loading as the runs, which can be due to a weak anchoring. This result prompts us to explore different linkers between magnetic nanoparticles and copper in order to decrease this leaching. Several linkers exhibiting different MNP-anchoring and Cu-chelating functions will be presented. Also, the successful extrapolation of this methodology to electron-poor or electron-rich substituted styrene derivatives will be demonstrated as well as the aziridination of long chain olefins which will be exhibited.

The first part of this dissertation is devoted to the study of an asymmetric [3+2] cycloaddition sequence developed in our laboratory. The cycloaddition sequence used a sulfonamide-based homoenolate equivalent which was cyclocondensed with a cyclic enone. The stereochemistry of the final product was fixed during the first step, the Michael addition to the enone. Our study focused thus on the Michael addition of sulfonamides to enones. We have synthesized a series of chiral and achiral sulfonamides. We then studied the regiochemistry and the stereochemistry of the addition of the anions derived from these sulfonamides to cyclohexenone. The presence of a heteroatom at the (gamma)-carbon of the sulfonamide was crucial for the regiochemical outcome of the reaction. The substituent on the sulfonamide also influenced the facial selectivity of the reaction with chiral sulfonamides, but had no influence on the diastereoselectivity with achiral sulfonamides. The sequence had been applied to various cyclenones. We were also able to apply the method to an acyclic enone with good enantioselectivities. However the method could not be applied to other Michael acceptors. Another part of the present work was devoted to search a new catalytic asymmetric cyclopentannulation sequence. Two different approaches were studied. Phase-transfer catalysis seemed the most appropriate strategy for our objective. We soon realized that sulfur-stabilized nucleophiles could not be used under these conditions. Ketals derived from 3-nitropropanal were thus chosen as potential annulation agents. The racemic version was quite efficient and could be applied to less active acceptors such as unsaturated lactams and lactones. Unfortunately we were not able to realize the reaction with good enantioselectivities. However two new catalysts, obtained by the reaction of cinchonine with 1- and 2-methylnaphthyl chloride, emerged as interesting candidates for the phase-transfer reactions. Organocatalysis was our second approach. The use of rubidium prolinate or the use of proline in the presence of a base proved to be very efficient and the Michael adducts could be obtained with good enantioselectivities. The Michael adducts were easily cyclized and the nitro group could be removed under mild conditions.

Meso 1,9-diketones (six to seven stereocenters)are readily obtained by stepwise or simultaneous two-directional aldol reactions of tetrahydro-4H-thiopyran-4-one with a thiopyran-derived aldehyde. Enantioselective enolizations of these diketones with the lithium amide from (R,R)-bis(1-phenylethyl)amine occur with simultaneous kinetic resolution to give the mono-TMS enol ethers in >90% yields based on recovered starting material (BORSM) and >90% ee. The developed methodology was applied in synthetic studies towards the asymmetric synthesis of denticulatin A.

Meso 1,9-diketones (six to seven stereocenters)are readily obtained by stepwise or simultaneous two-directional aldol reactions of tetrahydro-4H-thiopyran-4-one with a thiopyran-derived aldehyde. Enantioselective enolizations of these diketones with the lithium amide from (R,R)-bis(1-phenylethyl)amine occur with simultaneous kinetic resolution to give the mono-TMS enol ethers in >90% yields based on recovered starting material (BORSM) and >90% ee. The developed methodology was applied in synthetic studies towards the asymmetric synthesis of denticulatin A.

This dissertation investigates the design of a quarter-wave polarization transformer and presents some options for a high-performance polarizer in both normally incident and obliquely incident cases. Then, a novel concept for investigating polarization transformation is presented. Based on this concept, the broad axial ratio bandwidth polarizer, composed by anisotropic and chiral media, is accomplished using genetic algorithm. For the normally incident case, we present some methods to eliminate the reflection for designing novel high-performance polarizer in two situations. The polarizers provide perfect linear-to-circular polarization transformation without insertion loss at the center frequency. Then, two novel designs are presented for a high-performance quarter-wave polarizer in the obliquely incident case. In these designs, the material parameters of uniaxial media can be arbitrary. The polarizer is achieved by using only one layer of the uniaxial anisotropic medium without conventional anti-reflection coatings because of the unique property of the oblique incidence. The polarizer can produce a perfect linear-to-circular polarization transformation without any insertion loss at the center frequency. The equivalent circuit concept is presented to study polarization transformations. This concept is more convenient when dealing with polarization transformation problems in multiple layers. The anisotropic medium and the chiral medium can be regarded as circuit elements. Specifically, we show that anisotropic media can be seen as transformers and chiral media as transmission lines. Once the equivalent circuits are determined, the microwave network theory can be used to investigate the polarization transformation. An example is used to demonstrate the transformation from the horizontally polarized wave to the circularly polarized wave employing the equivalent circuit concept. Based on the equivalents concept, we present broad axial ratio bandwidth quarter-wave polarizer composed of mutilayered uniaxial anisotropic media and chiral media using genetic algorithm. In our design, the constitutive parameters of materials can be arbitrary. This broadband polarizer can be realized through the adjustment of the thickness of materials. The nearly optimal and suitable thickness of each cell is determined by using a genetic algorithm. Two numerical examples with three and five cells are presented to validate the design. The axial ratio bandwidths of about 84.1% and 92.8% can be achieved, more than double the maximum theoretical bandwidth for the case of the single uniaxial anisotropic slab.