Biscrown fluoroionophores: has the dye conformation an influence upon the formation of sandwich complexes in the ketocyanine series?

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Monosubstituted ferrocenyl chalcones : effect of structural changes upon the versatile ability to detect calcium by absorption spectroscopy

International audienceWe show how structural changes in the basic framework of ferrocenyl chalcone [(C5H5)Fe(C5 H4COCHdouble bondCHC6H4NEt2)] (1) induce different capabilities of detecting calcium by UV/vis absorption spectroscopy. In particular, compound 1, and its derivatives (2) and (3) incorporating a supplementary ethylenic unit into the conjugated link, allow a specific detection of calcium triflate with regard to calcium perchlorate. Investigations related to the unprecedented behaviour of these chalcone-like derivatives are presented. This study confirms that while the interaction of ligands 1–3 with calcium is centred on the CO group, the interaction of ligand 4 with calcium is aza-centered. The strength of these interactions was examined by processing the UV/vis absorption data with a curve fitting model. Remarkably, in the case of compound 4, the set of association constants issued from processing the absorption data was successfully used to fit the NMR data. In addition, mass spectrometry experiments provided strong support for the formation of the different species involved in the interaction of compounds 1–4 with calcium. This work underlines the importance of considering the nature of the salt used as well as the experimental conditions in cation detection processes

Intermolecular quenching of excited singlet states by ferrocenyl derivatives: study with ketocyanine dyes

International audienceThe fluorescence quenching of 1,5-bis[4-(diethylamino)phenyl]penta-1,4-dien-3-one (1), 1-[4-(diethylamino)phenyl]-5-phenylpenta-1,4-dien-3-one (2) and chalcone 3 (1-[4-(diethylamino)phenyl]but-1-en-3-one) was studied in acetonitrile using ferrocene and three commercially available derivatives, 1,1′-diacetylferrocene, acetylferrocene and 1,1′-dimethylferrocene. The spectroscopic and electrochemical characteristics of all the compounds were investigated. The feasibility of the quenching process was calculated, showing in particular that electron transfer was thermodynamically possible in every case. The steady-state fluorescence of the three organic dyes was then measured in the presence and in the absence of the ferrocenyl derivatives and the data were corrected for inner-filter effects. 1,1′-Diacetylferrocene and acetylferrocene proved to be the most efficient quenchers, and among the three dyes investigated, chalcone 3 was the most sensitive to the presence of the ferrocenyl derivatives. However, the fluorescence decay times of the ketocyanines were not affected by the presence of the ferrocene derivatives, indicating that quenching was not diffusion-controlled but rather the consequence of the formation of a ground state complex

La construction d’espaces francophones comme projet de société en milieu minoritaire

L’épanouissement de la francophonie canadienne à l’extérieur du Québec semble aujourd’hui se jouer sur la capacité de cette dernière à préserver, à développer et à contrôler des espaces francophones. En nous appuyant sur une recension des travaux de recherche qui traitent de la notion d’espace francophone, nous explorons le rôle que cette notion joue dans l’élaboration du projet de la francophonie canadienne de faire société. La notion d’espace francophone a auparavant pu épouser les contours, à l’échelle locale, de la paroisse et, à l’échelle nationale, du Canada français. Dans la foulée d’une redéfinition de la francophonie dans les années 1960, l’espace francophone s’est ensuite modulé à l’échelle des communautés francophones provinciales, qu’un réseau institutionnel permet de mettre en relation. Plus récemment, des définitions plus inclusives de l’espace francophone sont proposées en se fondant sur les compétences linguistiques individuelles, ce qui ne va pas sans soulever certaines questions.Today, it seems as if Canada’s Francophone community outside Québec will only flourish if it is able to preserve, develop and control Francophone spaces. Our article is an inventory of research projects that include this key notion in order to understand how the idea has been integrated into how these communities see themselves and how they want to constitute a society. Our literature review demonstrates that the notion of Francophone spaces has taken the shape, on the local level, of a parish, and on a larger scale, of French America and French Canada. When the concept of Francophonie was being redefined in the 1960s, the idea of Francophone spaces evolved to encompass provincial Francophone communities that could be linked by a network of institutions. More recently, we have more inclusive definitions of Francophone spaces based on individual language skills, and this in turn raises certain questions

Ferrocenyl compound as a multiresponsive calcium chemosensor with remarkable fluorescence properties in CH3CN

International audienceWe have synthesized a novel disubstituted ferrocenyl compound [Fe(C5H4CO(CHCH)2C6H4NEt2)2] (3) that displays a remarkable fluorescence quantum yield (1.1 × 10-1) in acetonitrile, and we have studied its capacity for calcium detection in depth using both electrochemical and optical techniques in this medium. The results of our NMR analysis reveal that the ligand−calcium interaction is CO-centered and that an uncommon equilibrium occurs between 3 and calcium triflate, involving five species of different stoichiometries. In contrast, our analysis of the UV−vis absorption data indicates that only three species of different stoichiometries are formed when calcium perchlorate is used with 3. Mass spectrometry measurements provide strong support for the formation of all these different species in solution. In addition, the electrochemical detection of calcium triflate by 3 leads to an irreversible FeII/FeIII oxidation process with an unusual negative shift (−60 mV) caused by the nBu4NBF4 salt effect on the Ca2+−3 interaction process. Compound 3 can also be an original optical probe to detect calcium perchlorate over a wide range of salt concentration by UV−vis absorption spectroscopy. The most original and intriguing property of compound 3 is that it exhibits an unprecedented “multistep” fluorescence behavior upon addition of this salt

Two electroactive ferrocenyl chalcones as original optical chemosensors for Ca2+ and Ba2+ cations in CH3CN

International audienceThe optical study of ferrocenyl ligands 1–2 is presented, and reveals several interesting points. Contrary to their monosubstituted counterparts, these ligands exhibit fluorescence properties in acetonitrile. They can detect calcium, and also barium, by four different techniques: NMR, electrochemistry, UV–Vis absorption spectroscopy and fluorimetry in the same solvent. Each ligand detects both salts in the same manner by UV–Vis absorption and by fluorimetry. The response depends on the nature of the N terminal groups of the ligand. In each case, the ligand–calcium interaction is complex and involves 3–5 species in equilibrium in solution. Their association constants have been determined by fitting the UV–Vis data. Remarkably, for 2 and the calcium salts, nearly the same set of association constants can be used to fit not only the UV–Vis data obtained with calcium triflate (in a restricted range of concentration) or with calcium perchlorate, but also the NMR data obtained with calcium triflate. Interestingly, these results strengthen the fact that, in this family of compounds, the azacrown derivatives are less sensitive to high calcium triflate concentrations than their simple N-alkyl homologues. It is noteworthy that the complex non-monotonous fluorescence behaviour of compounds 1 and 2 upon Ca2+ or Ba2+ addition is quite original for ferrocenyl chalcones. These ligands constitute scarce examples of multi-signalling fluorescent ferrocenyl chemosensors for Ca2+ and Ba2+ cations in CH3CN

Ca2+ vs. Ba2+ electrochemical detection by two disubstituted ferrocenyl chalcone chemosensors. Study of the ligand–metal interactions in CH3CN

International audienceWe show here that the disubstituted ferrocenyl chalcones 1 and 2 are good electrochemical sensors for calcium and barium in CH3CN. However, these two triflate salts are detected in a different way by both ligands. To clarify this point, a thorough and informative NMR study of the ligand–salt interactions is presented. The unusual shapes of the titration curves obtained depend on both the ligand and cation used. For example, they illustrate that ligand 1 mainly interacts with the metal by its CO functions, while ligand 2 also interacts by its azacrown groups. These curves also reflect complex equilibriums in solution involving several ligand–salt adducts detected by mass spectrometry. To evaluate the strength of these interactions, the association constants of all the species formed have been determined by fitting the NMR data. It is noteworthy that changing the diethylamino groups in molecule 1 by the azacrown residue enhances the selectivity for the calcium salt, as pointed out by the value of the association constant of the 2Ca2+ species. The synthesis of the protonated counterparts 3 and 4 was useful to clarify the electrochemical behaviour of 1 and 2. Although the two ligand–salt interactions present several common points, the whole results obtained allow us to propose an original explanation for the difference observed between the Ca2+ and Ba2+ electrochemical sensing

Spectroscopic Study of a Symmetrical Bis-crown Fluoroionophore of the Diphenylpentadienone Series

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Calcium Photorelease from a Symmetrical Donor−Acceptor−Donor Bis-crown-fluoroionophore Evidenced by Ultrafast Absorption Spectroscopy

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