Acid/base-triggered photophysical and chiroptical switching in a series of helicenoid compounds

International audienceA series of molecules that possess two quinolines, benzoquinolines, or phenanthrolines connected in a chiral fashion by a biaryl junction along with their water-soluble derivatives was developed and characterized. The influence of the structure on the basicity of the nitrogen atoms in two heterocycles was examined and the photophysical and chiroptical switching activity of the compounds upon protonation was studied both experimentally and computationally. The results demonstrated that changes in the electronic structure of the protonated vs. neutral species, promoting a bathochromic shift of dominant electronic transitions and alternation of their character from π-to-π* to charge-transfer-type, when additionally accompanied by the high structural flexibility of a system, leading to changes in conformational preferences upon proton binding, produce particularly pronounced modifications of the spectral properties in acidic medium. The latter combined with reversibility of the read-out make some of the molecules in this series very promising multifunctional pH probes

Broadband optical limiting optimisation by combination of carbon nanotubes and two-photon absorbing chromophores in liquids

International audienceWe report here on the optical limiting studies performed with nanosecond laser pulses on several families of multiphoton absorbers in chloroform, with carbon nanotubes suspended in solutions. Performances of these samples are compared with those of simple multiphoton absorber solutions and carbon nanotube suspensions, and the differences observed are interpreted in terms of cumulative NLO effects and adverse aggregation phenomenon

Chiral Trialkanolamine-Based Hemicryptophanes: Synthesis and Oxovanadium Complex

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Restricted Guest Tumbling in Phosphorylated Self-Assembled Capsules

International audienceABii diphosphonatocavitands self-assemble in chloroform solution to form dimeric molecular capsules. The molecular capsules can incarcerate an N-methylpyridinium or N-methylpicolinium guest. We have demonstrated that the supramolecular assembly acts as a molecular rotor as a result of the restricted motion of the guest inside the molecular cavity. In the solid state, X-ray diffraction analysis of the free host showed that two cavitands interact through strong hydrogen bonds to give the supramolecular self-assembled capsule. The solid-state structure of the N-methylpicolinium complex is comparable to that of the free host and indicates that the guest is not a prerequisite for the formation of the capsule. DOSY NMR studies provided a definitive argument for the formation of the free and complexed supramolecular capsule in CDCl3 solution. In solution, the tumbling of the N-methylpyridinium and N-methylpicolinium guests about the equatorial axes of the host can be frozen and differs by the respective energy barriers, with the larger picolinium substrate having a larger value (ΔG⧧ = 69.7 kJ mol−1) than the shorter pyridinium guest (ΔG⧧ = 44.8 kJ mol−1). This behavior corresponds to the restricted rotation of a rotator in a supramolecular rotor

Monodisperse fluorene oligomers exhibiting strong dipolar coupling interactions

International audienceWell-defined fluorene oligomers (n = 1 to 6) were prepared step by step using Suzuki and Yamamoto couplings, while absorption and photoluminescence properties evidenced very large dipolar coupling interactions between fluorene moieties

Selective Capture of Thallium and Cesium by a Cryptophane Soluble at Neutral pH

International audienceWe report in this article the synthesis of a asymmetrical cryptophane derivative (possessing only C3-symmetry) bearing three phenol groups and three other carboxylic acid functions, each of these groups on the aromatic rings. Thanks to isothermal titration calorimetry experiments, we show that this compound binds large monovalent cations, such as Cs+ and Tl+ with a binding constant significantly lower than its congeners bearing a larger number of phenol groups grafted on the benzene rings. However, higher selectivity for Cs+ and Tl+ was observed with this compound since it does not show any affinity for other alkali cations. More importantly, due to the greater solubility of this derivative in pure water, we show for the first time that effective thallium(I) complexation takes place at neutral pH. This result demonstrates that cryptophane derivatives decorated with a higher number of phenol groups are promising host molecules for removing traces of thallium(I) from aqueous phases at neutral pH or above

Synthesis and structure elucidation of large phosphorus macrocycles

The simple reaction between 1,omega-diamino derivatives and R-bis-(dimethylamino)-phosphane (R = CH3, C6H5), followed by an oxidation step led to the formation of the expected macrocyclic phosphorus compounds. By this way 17- to 27-membered macrocycles were easily obtained. During the synthesis, the formation of dimeric (40- and 52-membered rings) and trimeric (78-membered rings) macrocyclic species were obtained from 3 and 5 and fully characterized by NMR and mass spectrometry. The P(III) phosphorus species exchange in solution and the macrocycle/oligomers ratio is temperature and concentration dependent. The crystal structure analysis of macrocycles 1, 5, 7 and 8 show that voids are minimized in the solid so that the macrocyclic cavity is filled up with part of the molecule itself or with a guest molecule, when the size of the macrocycle does not allow molecular folding for self-filling the cavity

Near-Infrared Solid-State Emitters Based on Isophorone: Synthesis, Crystal Structure and Spectroscopic Properties.

International audienceA series of near-infrared solid-state emitters based on the dicyanoisophorone electron acceptor group was synthesized. The solid-state spectroscopic properties were studied by UV?visible absorption spectroscopy and fluorescence spectroscopy and analyzed in light of the single crystal structures obtained by X-ray diffraction. This series of push?pull dipolar fluorophores differing only by the substituent groups on the donor end display interesting solid-state emission properties on crystal with an emission in the near-infrared ranging from 710 to 790 nm. The origin of the emission depends on the nature of the substituent groups that influence the crystal packing and trigger the formation of long chain of emitting aggregates

Merging host-guest chemistry and organocatalysis for the chemical valorization of CO2

International audienceThe use of tri-and tetraphosphonate cavitand hosts in conjunction with tetrabutylammonium halide catalysts led to improved activity in the coupling of 1,2-epoxyhexane and CO 2. Catalytic efficiency of the supramolecular assembly strongly relies on both the structural features and binding properties of the cavitand host. Tetraphosphonate cavitand host (4iPO 1) was shown to impact more markedly n-Bu 4 NCl reactivity than triphosphonate counterpart (3iPO 3) due to its greater binding strength toward the ammonium cation as evidenced by titration experiments. The participation of acidic functional groups within the cavitand structure to activity enhancement was also clearly demonstrated. The best result was obtained with n-Bu 4 NI/3iPO 2 supramolecular assembly affording hexene carbonate in quantitative yield after 18 h of reaction. The improved performance observed with the cavitand 3iPO 2 relies on a double activation of both the nucleophile (halide) through efficient encapsulation of the ammonium cation and the substrate (epoxide) through hydrogen bonding