Claire Roiland

Multinuclear NMR as a tool for studying local order and dynamics in CH3NH3PbX3 (X = Cl, Br, I) hybrid perovskites

We report on 207Pb, 79Br, 14N, 1H, 13C and 2H NMR experiments for studying the local order and dynamics in hybrid perovskite lattices. 207Pb NMR experiments conducted at room temperature on a series of MAPbX3 compounds (MA = CH3NH3+; X = Cl, Br and I) showed that the isotropic 207Pb NMR shift is strongly dependent on the nature of the halogen ions. Therefore 207Pb NMR appears to be a very promising tool for the characterisation of local order in mixed halogen hybrid perovskites. 207Pb NMR on MAPbBr2I served as a proof of concept. Proton, 13C and 14N NMR experiments confirmed the results previously reported in the literature. Low temperature deuterium NMR measurements, down to 25 K, were carried out to investigate the structural phase transitions of MAPbBr3. Spectral lineshapes allow following the successive phase transitions of MAPbBr3. Finally, quadrupolar NMR lineshapes recorded in the orthorhombic phase were compared with simulated spectra, using DFT calculated electric field gradients (EFG). Computed data do not take into account any temperature effect. Thus, the discrepancy between the calculated and experimental EFG evidences the fact that MA cations are still subject to significant dynamics, even at 25 K.

A solid state highly emissive Cu(I) metallacycle: promotion of cuprophilic interactions at the excited states

The straightforward synthesis of a new Cu(i) metal-rich small metallacycle is presented. This compound is luminescent in the solid state with an emission quantum yield of 72% at room temperature and displays a pronounced reversible red-shift of its emission spectra upon cooling. Quantum chemical calculations reveal that these properties are governed by important geometrical relaxations that imply the formation of cuprophilic interactions at the excited states.

77Se solid-state NMR of As2Se3, As4Se4 and As4Se3 crystals: a combined experimental and computational study.

(77)Se NMR parameters for three prototypical crystalline compounds (As2Se3, As4Se4 and As4Se3) have been determined from solid-state NMR spectra in the framework of an investigation concerning AsxSe(1-x) glass structure understanding. Density functional NMR calculations using the gauge including projector augmented wave methodology have been performed on X-ray and optimized crystal structures for a set of selenium-based crystals. These theoretical results have been combined with the experimental data in order to achieve a precise assignment of the spectral lines. This work and the high sensitivity of solid-state NMR to local order show that the structure of As4Se3 should be reinvestigated using state-of-the-art diffraction techniques. Calculations performed on several molecules derived from the crystal structures have demonstrated the limited effect of interlayer or intermolecular interactions on the isotropic chemical shifts. These interactions are therefore not responsible for the unexpected large chemical shift difference observed between these three systems that could mostly be attributed to the presence of short rings.

Soil Calcium Availability Influences Shell Ecophenotype Formation in the Sub-Antarctic Land Snail, Notodiscus hookeri

Ecophenotypes reflect local matches between organisms and their environment, and show plasticity across generations in response to current living conditions. Plastic responses in shell morphology and shell growth have been widely studied in gastropods and are often related to environmental calcium availability, which influences shell biomineralisation. To date, all of these studies have overlooked micro-scale structure of the shell, in addition to how it is related to species responses in the context of environmental pressure. This study is the first to demonstrate that environmental factors induce a bi-modal variation in the shell micro-scale structure of a land gastropod. Notodiscus hookeri is the only native land snail present in the Crozet Archipelago (sub-Antarctic region). The adults have evolved into two ecophenotypes, which are referred to here as MS (mineral shell) and OS (organic shell). The MS-ecophenotype is characterised by a thick mineralised shell. It is primarily distributed along the coastline, and could be associated to the presence of exchangeable calcium in the clay minerals of the soils. The Os-ecophenotype is characterised by a thin organic shell. It is primarily distributed at high altitudes in the mesic and xeric fell-fields in soils with large particles that lack clay and exchangeable calcium. Snails of the Os-ecophenotype are characterised by thinner and larger shell sizes compared to snails of the MS- ecophenotype, indicating a trade-off between mineral thickness and shell size. This pattern increased along a temporal scale; whereby, older adult snails were more clearly separated into two clusters compared to the younger adult snails. The prevalence of glycine-rich proteins in the organic shell layer of N. hookeri, along with the absence of chitin, differs to the organic scaffolds of molluscan biominerals. The present study provides new insights for testing the adaptive value of phenotypic plasticity in response to spatial and temporal environmental variations.

DFT-assisted structure determination of α1- and α2-VOPO4: new insights into the understanding of the catalytic performances of vanadium phosphates

Structural investigations on vanadium phosphates, which are extensively used as catalysts in industry, often resulted in important advances in the understanding of the mechanisms driving the catalytic oxidation of light hydrocarbons. Layer translations in the two lamellar vanadium phosphates α1- and α2-VOPO4 phases identified during the catalysis were investigated by the combination of first-principles calculations, synchrotron X-ray powder diffraction, single-crystal X-ray diffraction and solid-state NMR. This analysis reveals an important feature: the α1-form is the only polymorph of VOPO4 to exhibit layer translations that prevent the formation of infinite VO6 chains. A detailed investigation of this structural characteristic in vanadium phosphates reveals the correlation between the presence of infinite VO6 chains and the catalytic performances of related phases.

Chitosan effects on glass matrices evaluated by biomaterial. MAS-NMR and biological investigations

Bioactive glass 46S6 and biodegradable therapeutic polymer (Chitosan: CH) have been elaborated to form 46S6-CH composite by freeze-drying process. The kinetics of chemical reactivity and bioactivity at the surface were investigated by using physicochemical techniques, particularly solid-state MAS-NMR. Immortalized cell line used to construct multicellular spheroids was employed as three-dimensional (3D) cell cultures for in vitro studies. Obtained results showed a novel structure of the composite; the chemical treatment (ultrasound, magnetic stirring, freeze drying process and lyophilization) led the bioactive glass particles to be loaded in the chitosan-based materials. 29Si and 31P MAS-NMR results showed the emergence of two new species, QSi3(OH) and QSi4, which are characteristic of the vitreous network dissolution in simulated body fluid (SBF). MAS-NMR also confirmed the formation of amorphous calcium phosphate (ACP) at the surface of the initial 46S6-CH. Three-dimensional (3D) cell cultures highlighted the effect of chitosan, where the cell viability reached up to 78% in 46S6-CH composite and up to 67% in 46S6. The association of (CH) and bioactive glass (BG) matrix promotes a highly significant bioactivity, demonstrating surface bone formation and satisfactory behavior in biological environment.

Direct Integration of Red-NIR Emissive Ceramic-like AnM6Xi8Xa6 Metal Cluster Salts in Organic Copolymers Using Supramolecular Interactions

Hybrid nanomaterials made of inorganic nanocomponents dispersed in an organic host raise an increasing interest as low-cost solution-processable functional materials. However, preventing phase segregation while allowing a high inorganic doping content remains a major challenge, and usual methods require a functionalization step prior integration. Herein, we report a new approach to design such nanocomposite in which ceramic-like metallic nanocluster compounds are embedded at 10 wt % in organic copolymers, without any functionalization. Dispersion homogeneity and stability are ensured by weak interactions occurring between the copolymer lateral chains and the nanocluster compound. Hybrids could be ink-jet printed and casted on a blue LED. This proof-of-concept device emits in the red-NIR area and generates singlet oxygen, O2 (1 Δg), of particular interest for lights, display, sensors or photodynamic based therapy applications.

Solventless and Metal‐Free Synthesis of High‐Molecular‐Mass Polyaminoboranes from Diisopropylaminoborane and Primary Amines

The solventless reaction of diisopropylaminoborane with n-butylamine, at room temperature, leads to a mixture of B(sp2) H-, B(sp3) H2 -, and B(sp3) H3 -containing species. At low temperature, the reaction outcome is completely modified, thus leading selectively to the formation of high-mass polybutylaminoborane. When extended to a variety of primary amines, under solventless conditions and at low temperature, this reaction provides a new, efficient, and direct metal-free access to high-molecular-mass polyaminoboranes in good to high yields under mild reaction conditions.

Strong solid-state luminescence enhancement in supramolecular assemblies of polyoxometalate and "Aggregation-Induced Emission"-active phospholium

Two new supramolecular fluorescent hybrid materials, combining for the first time [M6 O19 ]2- (M=Mo, W) polyoxometalates (POMs) and aggregation-induced emission (AIE)-active 1-methyl-1,2,3,4,5-pentaphenyl-phospholium (1+ ), were successfully synthesized. This novel molecular self-assembling strategy allows designing efficient solid-state emitters, such as (1)2 [W6 O19 ], by directing favorably the balance between the AIE and aggregation-caused quenching (ACQ) effects using both anion-π+ and H-bonding interactions in the solid state. Combined single-crystal X-ray diffraction, Raman, UV-vis and photoluminescence analyses highlighted that the nucleophilic oxygen-enriched POM surfaces strengthened the rigidity of the phospholium via strong C-H⋅⋅⋅O contacts, thereby exalting its solid-state luminescence. Besides, the bulky POM anions prevented π-π stacking interactions between the luminophores, blocking detrimental self-quenching effects.