Les travaux de cette thèse présentent le design et la synthèse de matériaux organiques/hybrides électro-photo modulables. La première partie détaille l’influence de groupements fluorés, attracteurs d’électrons, sur les mécanismes de transfert de charges au sein de triphénylamines : une nouvelle famille de molécules émissives, dont les longueurs d’onde d’émission couvrent une large gamme du visible est présentée. De plus, l’hydrophobicité induite par les atomes de fluor doit faciliter la préparation de nanobâtonnets préparés par mouillage d’une matrice d’alumine. Le reste du manuscrit s’intéresse à un second fluorophore organique, la tétrazine. Cette molécule possède une émission de fluorescence jaune qui peut être éteinte en présence de polluants riches en électrons. Immobilisée à la surface de nanoparticules de silice, la tétrazine conserve ces propriétés photophysiques et permet la préparation d’un dispositif solide capable de détecter des polluants aminés. L’incorporation au cœur de la nanoparticule d’un second fluorophore naphtalimide permet d’améliorer le rendement quantique de fluorescence et d’obtenir des nano-objets émettant une fluorescence blanche. Les propriétés photophysiques de ces objets sont décrites dans le manuscrit. Un dernier aspect détaille la synthèse et les études préliminaires de nouvelles dyades tétrazine-diacétylène. Les polydiacétylènes obtenus par polymérisation photo-induite possèdent plusieurs couleurs différentes. Cette partie vise à traiter l’influence des changements de phase du polymère sur l’émission de la tétrazine. / This Ph-D work deals with the design and the preparation of photo and electro-tunable materials. The first part of the manuscript deals with the influence of a fluorinated substitution onto a triarylamine moiety. The electron withdrawing fluorines modify the charge transfer process and customize the emission wavelength. In addition, the fluorinated groups increase the hydrophobic character of the material. This should be useful for the formation of organic nanorods via a template assisted method. The rest of the manuscript focuses on the tetrazine fluorophore which exhibits a yellow fluorescence that can be quenched in the presence of electron rich pollutants. A new methodology to covalently link a tetrazine derivative onto the surface of silica nanoparticle is discussed. The particles have similar photophysical properties as the tetrazine in solution allowing the use of this material as a solid sensing device. The incorporation into the silica core of a naphtalimide dye improves the overall fluorescence quantum yield of the system and provides nanoobjects emitting a white fluorescence. The photophysical phenomena involved in those particles are detailed in the manuscript. Finally, the synthesis and the photophysical properties of tetrazine-diacetylene dyads are discussed. Poly-diacetylenes prepared via a photopolymérisation process display different phases characterized by different colours. This part presents the preliminary results to understand the influence of the phase changes of the polymer on the tetrazine emission.

abstract: The proposed research mainly focuses on employing tunable materials to achieve dynamic control of radiative heat transfer in both far and near fields for thermal management. Vanadium dioxide (VO2), which undergoes a phase transition from insulator to metal at the temperature of 341 K, is one tunable material being applied. The other one is graphene, whose optical properties can be tuned by chemical potential through external bias or chemical doping. In the far field, a VO2-based metamaterial thermal emitter with switchable emittance in the mid-infrared has been theoretically studied. When VO2 is in the insulating phase, high emittance is observed at the resonance frequency of magnetic polaritons (MPs), while the structure becomes highly reflective when VO2 turns metallic. A VO2-based thermal emitter with tunable emittance is also demonstrated due to the excitation of MP at different resonance frequencies when VO2 changes phase. Moreover, an infrared thermal emitter made of graphene-covered SiC grating could achieve frequency-tunable emittance peak via the change of the graphene chemical potential. In the near field, a radiation-based thermal rectifier is constructed by investigating radiative transfer between VO2 and SiO2 separated by nanometer vacuum gap distances. Compared to the case where VO2 is set as the emitter at 400 K as a metal, when VO2 is considered as the receiver at 300 K as an insulator, the energy transfer is greatly enhanced due to the strong surface phonon polariton (SPhP) coupling between insulating VO2 and SiO2. A radiation-based thermal switch is also explored by setting VO2 as both the emitter and the receiver. When both VO2 emitter and receiver are at the insulating phase, the switch is at the “on” mode with a much enhanced heat flux due to strong SPhP coupling, while the near-field radiative transfer is greatly suppressed when the emitting VO2 becomes metallic at temperatures higher than 341K during the “off” mode. In addition, an electrically-gated thermal modulator made of graphene covered SiC plates is theoretically studied with modulated radiative transport by varying graphene chemical potential. Moreover, the MP effect on near-field radiative transport has been investigated by spectrally enhancing radiative heat transfer between two metal gratings. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2016

abstract: This research focuses mainly on employing tunable materials to achieve dynamic radiative properties for spacecraft and building thermal management. A secondary objective is to investigate tunable materials for optical propulsion applications. The primary material investigated is vanadium dioxide (VO2), which is a thermochromic material with an insulator-to-metal phase transition. VO2 typically undergoes a dramatic shift in optical properties at T = 341 K, which can be reduced through a variety of techniques to a temperature more suitable for thermal control applications. A VO2-based Fabry-Perot variable emitter is designed, fabricated, characterized, and experimentally demonstrated. The designed emitter has high emissivity when the radiating surface temperature is above 345 K and low emissivity when the temperature is less than 341 K. A uniaxial transfer matrix method and Bruggeman effective medium theory are both introduced to model the anisotropic properties of the VO2 to facilitate the design of multilayer VO2-based devices. A new furnace oxidation process is developed for fabricating high quality VO2 and the resulting thin films undergo comprehensive material and optical characterizations. The corresponding measurement platform is developed to measure the temperature-dependent transmittance and reflectance of the fabricated Fabry-Perot samples. The variable heat rejection of the fabricated samples is demonstrated via bell jar and cryothermal vacuum calorimetry measurements. Thermal modeling of a spacecraft equipped with variable emittance radiators is also conducted to elucidate the requirements and the impact for thermochromic variable emittance technology. The potential of VO2 to be used as an optical force modulating device is also investigated for spacecraft micropropulsion. The preliminary design considers a Fabry-Perot cavity with an anti-reflection coating which switches between an absorptive “off” state (for insulating VO2) and a reflective “on” state (for metallic VO2), thereby modulating the incident solar radiation pressure. The visible and near-infrared optical properties of the fabricated vanadium dioxide are examined to determine if there is a sufficient optical property shift in those regimes for a tunable device. / Dissertation/Thesis / Doctoral Dissertation Aerospace Engineering 2020