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Etudes photophysiques de nanoparticules moléculaires photochromes et fluorescentes préparées par photofragmentation laser

Abstract : Nanoparticles (NPs) of organic photochromic (cyclization/cycloreversion reaction between open and closed forms) materials (P1 and PF1) were prepared by the laser ablation method. Their size and their photophysical properties were investigated by microscopy and spectroscopy methods (UV-visible absorption, DLS, AFM, SEM). Regarding P1, the influence of the laser fluence and the temperature on the NPs size was evidenced. The competition between photochromism and ablation process was used to control the NPs formation by photochromism. An enhancement of the cycloreversion reaction occurred, via a stepwise two-photon absorption. In addition, in NPs, S1-S1 annihilation led to a further enhancement. Concerning PF1, a thorough study, involving quantum yields determination and DFT calculations was made. The cycloreversion quantum yield in solution shows an excitation wavelength dependence and several conformations of the open form were identified. NPs of PF1 were also prepared, and behave as a balanced trade-off between bulk (fluorescent, non photochromic) and solution (weakly fluorescent, photochromic): they allow an efficient photoswitching of the fluorescence. NPs size dependence of the cyclization/cycloreversion quantum yields and fluorescence properties was evidenced. The intermolecular energy transfer processes within the NPs enhances the fluorescence quenching during the photochromic reaction. These results are aimed to bring new perspectives results in the field of high-density digital information storage.
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https://tel.archives-ouvertes.fr/tel-00624375
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Submitted on : Friday, September 16, 2011 - 4:48:51 PM
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Jonathan Piard. Etudes photophysiques de nanoparticules moléculaires photochromes et fluorescentes préparées par photofragmentation laser. Autre. École normale supérieure de Cachan - ENS Cachan, 2011. Français. ⟨NNT : 2011DENS0028⟩. ⟨tel-00624375⟩

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