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Métalloporphyrines obéissantes : Détection et contrôle de la forme moléculaire dans une série de chiroporphyrines bridées

Abstract : A series of bridled chiroporphyrins and their metal complexes have been prepared, in which two n-methylene straps connect adjacent meso substituents by ester linkages. These compounds can exist as four atropisomers (alpha-alpha-alpha-alpha, alpha-beta-alpha-beta, alpha-alpha-alpha-beta or alpha-alpha-beta-beta) depending on the position of the meso groups relative to the macrocycle (alpha when above, beta when below). We have characterized the conformations of these chiral porphyrins by several spectroscopic techniques: proton nuclear magnetic resonance, electronic circular dichroism, and vibrational circular dichroism. The last two techniques are particularly useful for conformational characterization of the paramagnetic metallochiroporphyrins. The bridled chiroporphyrin with the shortest straps (n = 8) and its zinc complex can be isolated as the alpha-alpha-alpha-alpha atropisomer in the solid state, but in solution they are subject to atropisomeric equilibria, resulting in atropisomer distributions that are strongly solvent and concentration dependent. Axial ligation by piperidine has a strong influence on the atropisomer distribution of the zinc complex. Inspired by this remarkable conformational flexibility, we have investigated several ways of controlling the molecular shape of some metal complexes in this series. Our results show that it is possible to trigger large conformational changes (alpha-alpha-alpha-alpha ↔ alpha-beta-alpha-beta) of the nickel(II) and manganese(II/III) complexes with a chemical or redox signal that changes the occupancy of the stereochemically active 3dx2-y2 orbital. The observed conformational switches are reversible. The molecular bistability found in these systems is potentially interesting for applications in nanoelectronic devices such as non-volatile molecular memories.
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https://tel.archives-ouvertes.fr/tel-00129098
Contributor : Anna Castaings <>
Submitted on : Monday, February 5, 2007 - 5:31:56 PM
Last modification on : Wednesday, November 4, 2020 - 1:58:34 PM
Long-term archiving on: : Friday, November 25, 2016 - 2:21:10 PM

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Anna Castaings. Métalloporphyrines obéissantes : Détection et contrôle de la forme moléculaire dans une série de chiroporphyrines bridées. Autre. Université Joseph-Fourier - Grenoble I, 2006. Français. ⟨tel-00129098⟩

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