19 research outputs found
Controlled Growth of Porphyrin Wires at a SolidâLiquid Interface
Bis(zinc porphyrin) scaffolds bearing C8 or C18 alkyl chains and imidazole end groups selfâassembled in a headâtoâtail fashion into multiâporphyrin assemblies on both HOPG and mica. Due to weaker molecule surfaceâinteractions, longer arrays formed on mica than on HOPG. In both cases, it was essential first to generate monomers that were drop casted on the surface, then to allow time for the bis(zinc porphyrins) to assemble. Although thicker fibrous assemblies were observed with the C8 alkyl substituents than with the longer chains, noncovalent assemblies up to 1â
ÎŒm long were observed for each molecule. These investigations provide a reproducible, noncovalent method to grow porphyrin arrays that may be of interest in molecular electronics for charge transport
Ï-conjugated radicals for the construction and redox control of organized molecular assemblies
Lâobjectif de la thĂšse vise au dĂ©veloppement dâarchitectures molĂ©culaires et supramolĂ©culaires commutables par contrĂŽle rĂ©dox. La stratĂ©gie proposĂ©e repose sur lâexploitation du processus de Ï-dimĂ©risation subi par les radicaux cations de dĂ©rivĂ©s du viologĂšne comme force motrice pour la gĂ©nĂ©ration Ă©lectro-induite de mouvements intramolĂ©culaires. Nous dĂ©crivons la conception de nouvelles charniĂšres organiques Ă squelette calixarĂšne permettant dâaccĂ©der Ă des pinces molĂ©culaires. Convenablement fonctionnalisĂ©e par des mĂąchoires de type pyridine-pyridinium, le mouvement de la pince est dĂ©clenchĂ© par la combinaison dâune activation chimique et Ă©lectrochimique. Dans un deuxiĂšme exemple, nous montrons comment il est possible de verrouiller et dĂ©verrouiller les mouvements de la charniĂšre calixarĂšne en utilisant un rĂ©seau de liaisons hydrogĂšne intramolĂ©culaires. Nous dĂ©crivons Ă©galement la conception dâune charniĂšre inorganique originale fondĂ©e sur un complexe de palladium qui joue le rĂŽle du pivot dâun carrousel molĂ©culaire dont les bras Ă base de viologĂšne sont mis en rotation sous lâeffet dâune rĂ©duction Ă©lectrochimique centrĂ©e sur les motifs viologĂšnes. Le contrĂŽle rĂ©dox des phĂ©nomĂšnes dâauto-association au sein de polymĂšres de coordination dynamiques est Ă©galement abordĂ© au travers de deux exemples de pinces molĂ©culaires aux mĂąchoires fonctionnalisĂ©es soit par des briques auto-complĂ©mentaires, soit par des ligands bidentĂ©s. Dans un dernier exemple, un centre mĂ©tallique palladium est utilisĂ© Ă la fois comme vecteur de polymĂ©risation et comme charniĂšre pour la Ï-dimĂ©risation intramolĂ©culaire de ligands ditopiques Ă base de viologĂšnes.The aim of the thesis is to develop new concepts in the design of redox-switchable molecular and supramolecular architectures. The strategies which have been implemented rely on the Ï-dimerization of viologen radical cations as a driving force for the generation of electron-triggered intramolecular movements. Upon studying a series of viologen-appended calixarenes, we have established that bipyridinium radicals can be reversibly -dimerized under the joined effects of chemical (proton transfer) and electrochemical (electron transfer) stimulus. Our investigations also led to the discovery that a bis-pyridinyl appended calixarene intermediate is involved in a fully reversible redox-triggered sigma-dimerization process. We have also established that the ability of a phenol-containing calixarene to dimerize in its two electron reduced state depends on a subtle balance of weak interactions associated with hydrogen bond formation on the lower rim and orbital overlap between -radicals on the upper rim.We also demonstrate that inorganic hinges based on palladium complexes can be used as pivots in viologen-containing Ï-dimerizable architectures. The redox-controlled self-assemby of dynamic coordination polymers is also addressed through two examples of molecular tweezers, whose arms are functionalized by self-complementary complexing units or by bidentate ligands. In a last example, a palladium metal center is used both as a carrier of polymerization and as a hinge enabling the intramolecular Ï-dimerization of ditopic viologen-based ligands
Radicaux Ï-conjuguĂ©s pour la construction et le contrĂŽle redox d'assemblages molĂ©culaires organisĂ©s
The aim of the thesis is to develop new concepts in the design of redox-switchable molecular and supramolecular architectures. The strategies which have been implemented rely on the Ï-dimerization of viologen radical cations as a driving force for the generation of electron-triggered intramolecular movements. Upon studying a series of viologen-appended calixarenes, we have established that bipyridinium radicals can be reversibly -dimerized under the joined effects of chemical (proton transfer) and electrochemical (electron transfer) stimulus. Our investigations also led to the discovery that a bis-pyridinyl appended calixarene intermediate is involved in a fully reversible redox-triggered sigma-dimerization process. We have also established that the ability of a phenol-containing calixarene to dimerize in its two electron reduced state depends on a subtle balance of weak interactions associated with hydrogen bond formation on the lower rim and orbital overlap between -radicals on the upper rim.We also demonstrate that inorganic hinges based on palladium complexes can be used as pivots in viologen-containing Ï-dimerizable architectures. The redox-controlled self-assemby of dynamic coordination polymers is also addressed through two examples of molecular tweezers, whose arms are functionalized by self-complementary complexing units or by bidentate ligands. In a last example, a palladium metal center is used both as a carrier of polymerization and as a hinge enabling the intramolecular Ï-dimerization of ditopic viologen-based ligands.Lâobjectif de la thĂšse vise au dĂ©veloppement dâarchitectures molĂ©culaires et supramolĂ©culaires commutables par contrĂŽle rĂ©dox. La stratĂ©gie proposĂ©e repose sur lâexploitation du processus de Ï-dimĂ©risation subi par les radicaux cations de dĂ©rivĂ©s du viologĂšne comme force motrice pour la gĂ©nĂ©ration Ă©lectro-induite de mouvements intramolĂ©culaires. Nous dĂ©crivons la conception de nouvelles charniĂšres organiques Ă squelette calixarĂšne permettant dâaccĂ©der Ă des pinces molĂ©culaires. Convenablement fonctionnalisĂ©e par des mĂąchoires de type pyridine-pyridinium, le mouvement de la pince est dĂ©clenchĂ© par la combinaison dâune activation chimique et Ă©lectrochimique. Dans un deuxiĂšme exemple, nous montrons comment il est possible de verrouiller et dĂ©verrouiller les mouvements de la charniĂšre calixarĂšne en utilisant un rĂ©seau de liaisons hydrogĂšne intramolĂ©culaires. Nous dĂ©crivons Ă©galement la conception dâune charniĂšre inorganique originale fondĂ©e sur un complexe de palladium qui joue le rĂŽle du pivot dâun carrousel molĂ©culaire dont les bras Ă base de viologĂšne sont mis en rotation sous lâeffet dâune rĂ©duction Ă©lectrochimique centrĂ©e sur les motifs viologĂšnes. Le contrĂŽle rĂ©dox des phĂ©nomĂšnes dâauto-association au sein de polymĂšres de coordination dynamiques est Ă©galement abordĂ© au travers de deux exemples de pinces molĂ©culaires aux mĂąchoires fonctionnalisĂ©es soit par des briques auto-complĂ©mentaires, soit par des ligands bidentĂ©s. Dans un dernier exemple, un centre mĂ©tallique palladium est utilisĂ© Ă la fois comme vecteur de polymĂ©risation et comme charniĂšre pour la Ï-dimĂ©risation intramolĂ©culaire de ligands ditopiques Ă base de viologĂšnes
Hydrogen-Bond Controlled Ï-Dimerization in Viologen-Appended Calixarenes: Revealing a Subtle Balance of Weak Interactions
International audienc
Molécules et matériaux moléculaires redox- et photo-stimulables
National audienceLa conception de molĂ©cules et matĂ©riaux molĂ©culaires commutables dont les propriĂ©tĂ©s peuvent ĂȘtre rĂ©versiblementcontrĂŽlĂ©es et modulĂ©es sous lâeffet de stimuli externes est un domaine de recherche fascinant. Cet articleprĂ©sente quelques rĂ©sultats illustratifs de travaux concernant la conception de systĂšmes molĂ©culaires et supramolĂ©culairesstimulables par voies redox et optique, basĂ©s sur la mise en oeuvre dâentitĂ©s organiques viologĂšneet dimĂ©thyldihydropyrĂšne
Electron-Triggered Metamorphism in Palladium-Driven Self-Assembled Architectures
International audienceA metal-induced self-assembly strategy is used to promote the Ï-dimerization of viologen-based radicals at room temperature and in standard concentration ranges. Discrete box-shaped 2:2 (M:L) macrocycles or coordination polymers are formed in solution by self-assembly of a viologen-based ditopic ligand with cis-[Pd(en)(NO3)2], trans-[Pd(CH3CN)2(Cl)2], or [Pd(CH3CN)4(BF4)2]. Changing the redox state of the bipyridium units involved in the tectons, from their dicationic state to their radical cation state, results in a reversible âinflation/deflationâ of the discrete 2:2 (M:L) macrocyclic assemblies associated to a large modification in the size of their inner cavity. Viologen-centered electron transfer is also used to trigger a dissociation of the coordination polymers formed with tetrakis(acetonitrile)Pd(II), the driving force of the disassembling process being the formation of discrete box-shaped 2:2 (M:L) assemblies stabilized by Ï-dimerization of both viologen cation radicals
ORR activity of metalated phenanthroline-strapped porphyrin adsorbed on carbon nanotubes
International audienceDeveloping efficient noble metal-free systems for electrocatalysis and the reduction of oxygen (ORR) is crucial for hydrogen economy. Bioinspired hybrids combining iron or copper/iron porphyrins with multiwalled carbon nanotubes were tested for ORR using a rotating ring-disk electrode at pH 13 to 8. The porphyrin-nanotube hybrids exhibited better electrocatalytic properties than their constituents alone due to the electrical network formed by the nanotubes, and they reduced oxygen via a four-electron pathway to produce water. Whereas the presence of Cu was not mandatory to reduce oxygen, its presence improved ORR activity and decreased the overpotential compared to monometalic (iron porphyrin) hybrids.La conception de matériaux sans métaux nobles pour la réaction de réduction de l'oxygÚne (ORR) est cruciale pour le développement d'une économie basée sur l'hydrogÚne. Ici, des matériaux hybrides bioinspirés à base de porphyrines métallées et de nanotubes de carbone multi-parois ont été testés pour l'ORR avec un systÚme d'électrode disque-anneau entre pH 8 et 13. Les matériaux hybrides présentent systématiquement de meilleures propriétés électrocatalytiques que celles de leurs constituants pris individuellement et permettent de réduire l'oxygÚne par un processus à quatre électrons. La présence du cuivre dans les hybrides n'est pas obligatoire mais elle améliore légÚrement les propriétés électrocatalytiques
Reversible dimerization of viologen radicals covalently linked to a calixarene platform: Experimental and theoretical aspects
International audienceOn the ground of advanced electrochemical, spectroscopic and theoretical data, we have demonstrated that two bipyridinium radicals introduced on the lower rim of a calixarene skeleton can be efficiently and reversibly pi-dimerized. A detailed electrochemical investigation supports the conclusion that the non-covalent association between both electrogenerated radical-cations proceeds intramolecularly with a fast kinetics, the electrochemical behaviour being mostly limited, in the accessible scan range, by the kinetics of the heterogeneous electron transfer. Further insights into the structure and stability of a series of covalently linked pi-dimers have been provided by DFT calculations carried out at various computational levels. A major result of these theoretical investigations is that solvents and dispersion-correcting potentials have to be considered to accurately model the non-covalent interactions involved in pi-dimer complexes
Electron-Triggered Metamorphism in Porphyrin-Based Self-Assembled Coordination Polymers
International audienc