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Week-long-lifetime microwave spectral holes in an erbium-doped scheelite crystal at millikelvin temperature
No full textInternational audienceRare-earth-ions (REI) doped crystals have remarkable optical and spin properties characterized by narrow homogeneous linewidths, which can be studied despite the large inhomogeneous broadening of the ensemble line through spectral hole burning (SHB). Here, we report SHB spectroscopic measurements in a scheelite crystal of CaWO4 by pumping the spin transition of a paramagnetic REI (Er3+) at microwave frequency and millikelvin temperatures, with nuclear spin states of neighboring 183W atoms serving as the auxiliary levels. The repeated application of pairs of microwave pulses generates a periodic modulation of the Er3+ density profile, which we observe spectrally and in the time-domain as an accumulated echo. The lifetime of the holes and accumulated echoes rises steeply as the sample temperature is decreased, exceeding a week at 10mK. Our results demonstrate that millikelvin temperatures can be beneficial for signal processing applications requiring long spectral hole lifetimes
NaSICON NaFe2PO4(SO4)2 revisited: insights into the crystal structure and electrochemical performance
No full textInternational audienceWith the aim to meet the needs for positive electrode materials for Na-ion batteries, based on abundant elements, synthesis routes using two different Fe3+ precursors were explored for the preparation of a pure mixed phosphate-sulfate NaSICON-type compound, NaFe23+PO4(SO4)2 (NFPS). Interestingly, a structural model described in the R-3 space group is found from careful analysis of X-ray, neutron, and electron diffraction. Atoms P and S (and thus, PO4 and SO4 anionic groups) are statistically distributed within the polyanionic framework, with a splitting of the conventional Na2 3b site into two positions 3a and 18f. Na-half cells with NFPS as a positive electrode material delivered 126 mAh/g, nearly the full theoretical capacity, at a cycling rate of D/30–C/30 (i.e., the exchange of 2 Na+ in 30 h).</p
Ansa -effects in alkaline earth metal octaphenylmetallocenophanes and a derived ansa -ferrocene
No full textInternational audienceThe synthesis and structural characterisation of a series of alkaline earth ansa-octaphenylmetallocenes (Mg, Ca, Sr, Ba) bearing an ethylene bridge are described. The complexes [AE(C5Ph4CH2)2(thf)n] (AE = Mg (1), Ca (2) n = 1; AE = Sr (3), Ba (4), n = 2) were obtained through reductive dimerisation of 1,2,3,4-tetraphenylfulvene, facilitated by zero-valent metals and fully characterised by NMR spectroscopy. Singlecrystal XRD studies reveal distinct binding differences of the Cp ligands to Mg in complex 1 compared to the heavier analogues (η3 vs. η5). Complex 3 is the first structurally characterised ansa-metallocene complex of Sr. An ansa-effect was observed for the Ba complex 4 which showed good stability at room temperature in contrast to the previously described non-bridged analogue. Efficient transmetallation from the Ca ansa complex 2 to FeCl2 provided the new ansa-ferrocene complex [Fe(C5Ph4CH2)2] (5). Structural, spectroscopic and electrochemical properties of this bent ferrocenophane complex were compared to those of the known unbridged octaphenylferrocene
The intriguing role of L-cysteine on the modulation of chiroplasmonic properties of chiral gold nano-arrows
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Le couplage croisé déshydrogénant pallado-catalysé : un mode de valorisation des terpènes
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Cobalt Pyrene‐Quaterpyridine Molecular Complex Immobilized on Functionalized Multi‐Walled Carbon Nanotubes as a Robust Hybrid Catalyst for Efficient Electrochemical Reduction of CO<sub>2</sub>
No full textInternational audienceMolecular complexes immobilized on conductive carbon supports is a promising strategy for designing efficient electrocatalysts of CO2 reduction reaction (CO2RR). However, most immobilized catalysts suffer from low catalytic activity and durability due to weak catalyst-support interactions. Herein, modifications of Co quaterpyridine complex (Coqpy) with a pyrene group and multi-walled carbon nanotubes (MWCNT) with carboxyl or amide groups have been made, resulting in a highly efficient and stable hybrid catalyst. The carboxyl groups on MWCNT can effectively bind to Co centers by axial coordination; which allow for loading more electroactive Co complex, facilitate interfacial electron transfer, and lower the energy barrier for CO2RR. A 2.6-fold increase in CO yield and a higher Faradaic efficiency (97.5% vs 83.6% at 423 mV overpotential) are obtained compared with the hybrid catalyst without carboxyl group. While, the pyrene group induced more substantial π–π interactions, leading to an enhanced electronic coupling between MWCNT and Coqpy, and enhanced hybrid stability, resulting in a ≈ 4.4-fold higher CO turnover frequency than Coqpy. Overall, the outstanding performance of the modified hybrid catalyst (turnover number up to 570000, Faradaic efficiency close to 100%) provides new mechanistic insights and design strategy for efficient and durable CO2RR based on heterogenized molecular catalysts
Evaluation of Ligand Influence on Gold(I)-Alkyne Complexes Using (Threshold) Collision Induced Dissociation
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All-microwave spectroscopy and polarization of individual nuclear spins in a solid
No full textInternational audiencePushing the sensitivity of nuclear magnetic resonance spectroscopy to the single spin level would have a major impact in chemistry and biology and is the goal of intense research efforts. We report magnetic resonance spectroscopy measurements of individual nuclear spins in a crystal coupled to a neighboring paramagnetic center, detected using microwave fluorescence at millikelvin temperatures. We observe real-time quantum jumps of the nuclear spin state, a proof of their individual nature. By driving the forbidden transitions of the coupled electron-nuclear spin system, we also achieve single-spin solid-effect dynamical nuclear polarization. Relying exclusively on microwave driving and microwave photon counting, the methods reported here are, in principle, applicable to a large number of electron-nuclear spin systems, in a wide variety of samples
Sequential and Time-Controlled Sol-Gel Transitions by the Mechanical Switching of Molecular Tweezers
No full textInternational audienceControlling the motion of molecular machines to influence higher-order structures is well-established in biological systems but remains a significant challenge for synthetic analogs. Herein, we aim to harness the mechanical switching of switchable molecular tweezers to modulate their self-assembly and produce stimuli-responsive organogels. We report a series of terpy(Pt-salphen)2 molecular tweezers functionalized with alkyl chains that act as low-molecular-weight gelators (LMWGs) in their open conformation. The resulting organogels were thoroughly characterized by SEM, cryo-TEM, SAXS, and rheology. The macroscopic transition from gel to solution was achieved by the cation-induced closing of the tweezers, which triggers their substantial structural reorganization. Reversible sol-gel transitions were achieved through the sequential addition of chemical stimuli or by a decomposable acid in a time-controlled operation. Such transient disassembly process regulated by a chemical fuel enables multiple gelation cycles with minimal waste while maintaining stable rheological properties. These results underscore the potential of switchable molecular tweezers in creating advanced stimuli-responsive materials
Tuning the size of poly(butylene oxide) nanoparticles by microfluidic-assisted nanoprecipitation
No full textInternational audienceMicrofluidic-assisted nanoprecipitation provides precise control over formulation conditions, enabling for the design of nanoparticles with highly tunable properties. This study explores the influence of channel geometry, flow dynamics, and polymer concentration on the size and polydispersity of poly(butylene oxide) (PBO) nanoparticles. PBO is a hydrophobic polymer with a low glass transition temperature (Tg = –71 °C) that typically forms large nanoparticles (>176 nm) via bulk nanoprecipitation, as well as aggregates ranging from 3000–5000 nm. Using a hydrodynamic flow-focusing Ψ-geometry, we demonstrate that higher total flow rates increase convective mixing, reduce mixing times, and produce smaller, more monodisperse PBO nanoparticles. A comparative analysis of Ψ- and T-channel geometries across various dimensions revealed that Ψ-geometries consistently outperformed T-geometries due to their superior mixing efficiency. Decreasing the channel dimensions to 20 µm further improved mixing by shortening diffusion lengths and accelerating solvent–antisolvent interdiffusion. Using the Ψ-geometry, nanoparticles as small as 66 nm were achieved, whereas T-geometries produced significantly larger particles (>500 nm). A linear trend between particle size and total flow was observed, best described by a power-law relationship, linking flow rate—and by extension, Reynolds number—to mixing speed and nanoparticle size. These findings highlight the pivotal role of microfluidic design and flow control in tailoring nanoprecipitation for low-Tg, hydrophobic polymers such as PBO. This approach shows promising potential for the encapsulation and delivery of hydrophobic drugs