Synthèses et études de systèmes supramoléculaires photocommutables (récepteurs à ion et molécules entrelacées)

Des azobenzènes photochromiques ont été intégrés à des macrocycles synthétiques pour moduler photochimiquement la chélation de différents ions qui jouent un rôle essentiel dans les processus biologiques. La photocommutation de ces récepteurs a été étudiée (rendements quantiques, réversibilité, état photostationnaire) et les constantes de stabilité ont été déterminées. Le développement d un récepteur biocompatible du Ca2+ (BAPTA) a permis de moduler la concentration de Ca2+ dans une solution aqueuse avec la lumière. Les molécules entrelacées sont également un sujet majeur dans le domaine de la chimie supramoléculaire. Une méthode de macrocyclisation photochimique, basée sur la dimérisation de l anthracène, a été appliquée à des assemblages supramoléculaires dans le but de modifier leur topologie et de développer une nouvelle stratégie de photocaténation. En parallèle, un rotaxane a été réalisé en ajoutant des groupements encombrants sur les anthracènes par une réaction de Diels-Alder.As the availability of ions plays a key role in biological processes, photochromic azobenzene macrocycles were synthetized to photochemically modulate chelation of different ions in various media. The photoswitching of these receptors was evaluated (quantum yields, reversibility, photostationary state) as well as binding constants. Integrating a biocompatible Ca2+ receptor (BAPTA) with azobenzene enabled the modulation of calcium concentration in aqueous solution and to reversibly switch the fluorescence emission of a molecular probe based on photoinduced electron transfer. Interlocked molecules are also a major topic in the field of supramolecular chemistry. A Photochemical macrocyclization method, based on the dimerization of anthracene, was applied to supramolecular assemblies in order to change their topology and develop a new strategy of photocatenation. In parallel, a rotaxane was achieved by adding bulky groups on anthracenes by a Diels-Alder reaction.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF

Designed long lived emission from CdSe quantum dots by reversible electronic energy transfer with a surface bound chromophore

The size-tunable emission of luminescent quantum dots (QDs) makes them highly interesting for applications that range from bioimaging to optoelectronics. For the same applications, engineering their luminescence lifetime – in particular, making it longer – would be as important; however, no rational methodology to reach this goal is available to date. Here we describe a strategy to prolong the emission lifetime of QDs by electronic energy shuttling to the triplet excited state of a surface-bound molecular chromophore. To implement this idea we made CdSe QDs of different sizes, and we self-assembled them with a pyrene derivative. We observed that the conjugates exhibit delayed luminescence, with emission decays that are prolonged by more than 3 orders of magnitude compared to the parent CdSe QDs (lifetimes up to 330 s). The mechanism invokes unprecedented reversible quantum dot-to-organic chromophore electronic energy transfer

Aromatic oligoamide foldamers as versatile scaffolds for induced circularly polarized luminescence at adjustable wavelengths

International audienceQuinoline oligoamide foldamers appended with non-chiral fluorophores and derivatized with a camphanyl chiral inducer display strong chiroptical properties at tunable wavelengths as proved by CD and CPL spectroscopies. Induced CPL activity with high luminescence dissymmetry factors was observed in the visible range at wavelengths specific to the fluorophores

Photolariats: synthesis, metal ion complexation and photochromism

International audiencePhotolariat development, as an extension to the family of synthetic photochromic crown ether receptors, or photocrowns, is reported. Incorporated additional chelating groups, namely two anisoles or thioanisoles, contribute in completing the metal ion coordination sphere with different affinities and selectivities for a range of ions. Single-crystal X-ray diffraction analysis suggests that the thermally stable trans-form of the receptor is unsuitable for ion binding, consistent with spectrophotometric and NMR titration results, which is largely improved in the cis-form as the basis for the photocontrolled ion coordination/ejection. In terms of the azobenzene-containing receptor photochemistry, a photostationary state highly enriched in the cis-form (94:6, cis-/trans-) is reached, with slow thermal return (1.1-1.4 × 10− 5 s− 1) in the dark, which can undergo multiple cycles without discernable photodegradation

Dynamics of ion-regulated photoinduced electron transfer in BODIPY-BAPTA conjugates

International audienceEfficient Ca2+-switched fluorescent sensors, where fluorescence output is governed by a light-activated ion-gated electron transfer pathway, can be obtained on combining BODIPY chromophores with a readily oxidized biocompatible and selective BAPTA receptor. Herein we report the synthesis and studies of two such conjugates, which vary in the nature of the spacer separating the two electroactive components, namely none (1) or phenyl (2). Single crystal X-ray crystallography and molecular modelling structures and calculations give information on molecular and electronic structure, while steady-state fluorescence experiments show high Ca2+-induced fluorescence enhancement factors of 122 and 23 and Kd values of 0.50 μM and 0.13 μM for 1 and 2, respectively. Notably, studies of the ultrafast photoinduced processes (through transient absorption spectroscopy) give access to electron transfer dynamics in pseudophysiological media as well as in a polar non-protic solvent and information about the fate of the excited molecules in the presence and absence of calcium. In water, electron transfer rates as high as 3.3 × 1012 s−1 and 8.3 × 1011 s−1 are measured for the ion-free, directly connected conjugate and the variant incorporating a phenyl spacer, respectively. This electron transfer pathway is efficiently blocked by the presence of an ion, restoring fluorescence

Org. Chem. Front.

The synthesis and characterization of an original π-extended cationic azahelicene is reported. The phenanthrene-fused aza[7]helicene derivative encompasses a total of ten aromatic fused rings leading to a dissymmetric yet helically folded structure, as revealed by NMR and X-ray diffraction analyses. The polyaromatic and cationic nature of the new azahelicenium makes it soluble in both organic and aqueous media, which allowed photophysical studies in solvents of different polarities. The extended chromophoric species demonstrates a broad absorption over the whole visible range and orange-red fluorescence emission. Chiral resolution of the racemate was performed subsequently, affording two optically pure and configurationally stable azahelicenium enantiomers. Multi-band circular dichroism and long-wavelength circularly polarized emission were observed, associated with remarkable absorption and luminescence dissymmetry factors, both in organic and aqueous media.Program Initiative d’Excellenc

Teaching Story without Struggle: Using Graded Readers and Their Audio Packs in the EFL Classroom

In recent years the support for extensive reading (ER) in English as a second or foreign language (ESL/EFL) programs has been compelling. When practicing extensive reading, the learner reads a wide variety of texts for pleasure and achieves a general understanding of the content while deciphering unknown words through context. This approach contrasts with intensive reading, a more traditional approach based on a slow, careful reading of a text, with goals of complete comprehension and the identification of specific details and information

Transfert d'énergie réversible dans des systèmes supramoléculaires organiques-inorganiques

Une approche innovante a récemment été développée afin de prolonger la durée de vie de luminescence de complexes métal-polypyridine où le mécanisme est basé sur un transfert d'énergie réversible entre deux états triplets isoénergétiques. Ces derniers sont localisés d'une part sur la moitié inorganique (3(exposant)MLCT) et d'autre part sur un chromophore organique distinct (3(exposant)LC). Des complexes de ruthénium (II) bichromophoriques ont ainsi été introduits dans différents milieux biomimétiques et abiotiques et leurs comportements photophysiques ont été étudiés. L'intervention des processus considérés dans une réaction de séparation de charge photoinduite a été démontrée et a accru l'efficacité du système de 300% vis-à-vis du complexe de référence. Cette stratégie a également été étendue à des complexes de cuivre (I) donnant des molécules dotés de propriétés à l'état excité inédites et a été appliquée dans un système de conversion montante dans un nouveau mécanisme muticomposante.BORDEAUX1-BU Sciences-Talence (335222101) / SudocSudocFranceF