Isabelle Maurin

Mechanochromic and Thermochromic Luminescence of a Copper Iodide Cluster

The mechanochromic and thermochromic luminescence properties of a molecular copper(I) iodide cluster formulated [Cu(4)I(4)(PPh(2)(CH(2)CH=CH(2)))(4)] are reported. Upon mechanical grinding in a mortar, its solid-state emission properties are drastically modified as well as its thermochromic behavior. This reversible phenomenon has been attributed to distortions in the crystal packing leading to modifications of the intermolecular interactions and thus of the [Cu(4)I(4)] cluster core geometry. Notably, modification of the Cu-Cu interactions seems to be involved in this phenomenon directly affecting the emissive properties of the cluster.

Molecular migration mechanism for laser induced surface relief grating formation

Direct and reversible holographic recording of surface-relief gratings in azo-dye polymers was recently evidenced using atomic force microscopy. Irradiation with an interference pattern of polarized laser beams was observed to lead to substantial mass-transport. In typical experiments, the wavelength of the laser was chosen to be near the absorption of the chromophores. The surface gratings have a negative amplitude which can be as large as twice the polymer film thickness. The origin of such photo-driven mass transport is still unclear. We provide here experimental evidence of a migration of the chromophores from high to low intensity regions. It indicates that, in such doped or grafted guest-host systems, polymer chain migration is a result of the guest chromophores photoinduced movements. This is in good agreement with our recently developed model of azo-dye photoinduced translation diffusion.

Multifunctional Rare-Earth Vanadate Nanoparticles: Luminescent Labels, Oxidant Sensors, and MRI Contrast Agents

Collecting information on multiple pathophysiological parameters is essential for understanding complex pathologies, especially given the large interindividual variability. We report here multifunctional nanoparticles which are luminescent probes, oxidant sensors, and contrast agents in magnetic resonance imaging (MRI). Eu(3+) ions in an yttrium vanadate matrix have been demonstrated to emit strong, nonblinking, and stable luminescence. Time- and space-resolved optical oxidant detection is feasible after reversible photoreduction of Eu(3+) to Eu(2+) and reoxidation by oxidants, such as H2O2, leading to a modulation of the luminescence emission. The incorporation of paramagnetic Gd(3+) confers in addition proton relaxation enhancing properties to the system. We synthesized and characterized nanoparticles of either 5 or 30 nm diameter with compositions of GdVO4 and Gd0.6Eu0.4VO4. These particles retain the luminescence and oxidant detection properties of YVO4:Eu. Moreover, the proton relaxivity of GdVO4 and Gd0.6Eu0.4VO4 nanoparticles of 5 nm diameter is higher than that of the commercial Gd(3+) chelate compound Dotarem at 20 MHz. Nuclear magnetic resonance dispersion spectroscopy showed a relaxivity increase above 10 MHz. Complexometric titration indicated that rare-earth leaching is negligible. The 5 nm nanoparticles injected in mice were observed with MRI to concentrate in the liver and the bladder after 30 min. Thus, these multifunctional rare-earth vanadate nanoparticles pave the way for simultaneous optical and magnetic resonance detection, in particular, for in vivo localization evolution and reactive oxygen species detection in a broad range of physiological and pathophysiological conditions.

Synthesis, morphology and compositional evolution of silicon nanowires directly grown on SnO2 substrates

We here propose an all-in situ method for growing vapor-liquid-solid (VLS) silicon nanowires (SiNWs) directly on SnO(2) substrates in a plasma-enhanced chemical vapor deposition system. The tin catalysts are formed by a well-controlled H(2) plasma treatment of the SnO(2) layer. The lowest temperature for the tin-catalyzed VLS SiNWs growth in a silane plasma is ∼250u2009°C. The effects of substrate temperature and H(2) dilution of silane on the morphology and compositional evolution of the SiNWs were systematically investigated. The catalyst content in the SiNWs can be effectively controlled by the deposition temperature. Moreover, enhanced absorption (down to ∼1.1xa0eV) is achieved due to the strong light trapping and anti-reflection effects in the straight and long tapered SiNWs.

Controlled growth of core@shell heterostructures based on Prussian blue analogues

This work aims to develop a controlled strategy for the growth of multifunctional core@shell nanoparticles based on Prussian blue analogues. We mainly focussed our attention on Rb0.45Co[Fe(CN)6]0.8·3H2O@Rb0.2Ni[Cr(CN)6]0.7·zH2O particles, which combine a photoswitchable (photo-magnetic/-chromic) core with a ferromagnetic shell. The control of the chemical composition in the heterostructure is a key point to obtain the expected magnetic, optical and structural properties. We found that the removal of the unreacted species by washing after the growth of the primary particles led to an irreversible aggregation attributed to the desorption of stabilizing [Fe(CN)6] surface units. We showed that this difficulty could be overcome by washing the particles in a solution containing chromicyanide ions, which are precursors of the Rb0.2Ni[Cr(CN)6]0.7·zH2O shell phase, thus avoiding a contamination of the shell. Both X-ray diffraction and magnetic measurements confirmed that a controlled shell of the desired composition could be obtained this way.

Photocatalytic activity of mesoporous films based on N-doped TiO2 nanoparticles

TiO2 based photocatalytic coatings are currently restricted to outdoor applications due to the requirement of UV light. Nitrogen doping of TiO2 was used here to activate them in indoor conditions for self-cleaning applications. We developed an original process, allowing nitridation of anatase nanoparticles dispersed within a porous silica matrix, at high temperatures (up to 800 °C), with neither structural change, nor aggregation and growth of the nanoparticles. After chemical dissolution of the silica, N-doped TiO2 particles were dispersed in water allowing the preparation of both concentrated colloidal aqueous dispersions and transparent sol–gel films in which N-doped particles are dispersed in a sol–gel silica binder with a controlled porosity. The N-doped TiO2 nanoparticles present visible light photocatalytic activity due to the presence of bulk nitrogen species. We showed that the photocatalytic activity of the films can be improved by an additional oxidative thermal treatment suppressing the Ti3+ ions which act as recombination centers in TiO2. We thus succeeded in preparing coatings twenty times more active than the reference under irradiation at 390 nm by monitoring the degradation of the Rhodamine 6G dye.

Mechanochromic Luminescence of Copper Iodide Clusters

Luminescent mechanochromic materials are particularly appealing for the development of stimuli-responsive materials. Establishing the mechanism responsible for the mechanochromism is always an issue owing to the difficulty in characterizing the ground phase. Herein, the study of real crystalline polymorphs of a mechanochromic and thermochromic luminescent copper iodide cluster permits us to clearly establish the mechanism involved. The local disruption of the crystal packing induces changes in the cluster geometry and in particular the modification of the cuprophilic interactions, which consequently modify the emissive states. This study constitutes a step further toward the understanding of the mechanism involved in the mechanochromic luminescent properties of multimetallic coordination complexes.

A protected annealing process for the production of high quality colloidal oxide nanoparticles with optimized physical properties

Colloidal synthesis of inorganic materials is usually achieved in solvents under milder conditions of temperature than those usually used for the preparation of bulk compounds. As commonly shown on oxide nanoparticles with sizes of more than typically 20 nm, this leads to particles exhibiting an altered crystallinity with the presence of more or less extended defects that may impact the physical properties of the particles. Considering that post-annealing treatments on powders of nanoparticles inevitably lead to their sintering (i.e. growth and irreversible aggregation), the influence of these defects has rarely been discussed. For a few years, we have been investigating a post-synthesis process of “protected annealing”. The basic principle relies on thermal treatment of preformed particles that have been previously dispersed into a sol–gel silica matrix. After annealing at temperatures up to 1000 °C, the dissolution of the host matrix allows recovery of a suspension of particles with the same size as the pristine particles and an almost perfect crystallinity. Investigation of the physical properties of these particles permitted us to show their optimized properties, thus discriminating the influence of altered crystallinity compared to small size or surface effects and high surface area. Results are presented in the case of oxide phosphors (YVO4:Eu, YAG:Ce), photocatalytic TiO2 and magnetic γ-Fe2O3 particles. Finally, an extension of the process is shown in the case of a reactive protected annealing, when the thermal treatment is associated with a change of chemical composition of the particles, thus allowing the investigation of systems that are difficult to obtain through conventional colloid chemistry. This latter strategy is presented in the cases of Zn2SiO4:Mn nanophosphors, Co-doped γ-Fe2O3 and N-doped TiO2.

Impact of crystalline packing on the mechanochromic luminescence properties of copper based compounds: towards functional coatings

Mechanochromic luminescent materials exhibit a reversible change of the emission wavelength in response to external mechanical forces. These properties are particularly appealing for applications as memory or sensor devices. In order to rationally design and develop such materials, an in-depth understanding of the mechanochromic mechanisms is highly required. In this work, a comparative study of two copper iodide compounds whose difference lies in the subtle modification of the ligands has been conducted. These two clusters present very close crystalline structures but strikingly different optical properties with only one of them exhibiting luminescence mechanochromic properties. Structural and optical characterizations demonstrate that the two clusters endorse different internal stresses due to slight differences in the crystal packing controlled by the nature of the ligands. The release of these constraints upon mechanical solicitation leads to modification of the intramolecular interactions and is at the origin of the observed mechanochromic properties. Additionally, by taking advantage on the sensitive and highly contrasting mechanochromic properties of the clusters, the preparation and characterization of functional coatings on a glass substrate are also presented. An intense signal is observed upon mechanical solicitation which can be erased upon mild thermal treatment.

Engineered Ferritin for Magnetogenetic Manipulation of Proteins and Organelles Inside Living Cells

Magnetogenetics is emerging as a novel approach for remote-controlled manipulation of cellular functions in tissues and organisms with high spatial and temporal resolution. A critical, still challenging issue for these techniques is to conjugate target proteins with magnetic probes that can satisfy multiple colloidal and biofunctional constraints. Here, semisynthetic magnetic nanoparticles are tailored based on human ferritin coupled to monomeric enhanced green fluorescent protein (mEGFP) for magnetic manipulation of proteins inside living cells. This study demonstrates efficient delivery, intracellular stealth properties, and rapid subcellular targeting of those magnetic nanoparticles via GFP-nanobody interactions. By means of magnetic field gradients, rapid spatial reorganization in the cytosol of proteins captured to the nanoparticle surface is achieved. Moreover, exploiting efficient nanoparticle targeting to intracellular membranes, remote-controlled arrest of mitochondrial dynamics using magnetic fields is demonstrated. The studies establish subcellular control of proteins and organelles with unprecedented spatial and temporal resolution, thus opening new prospects for magnetogenetic applications in fundamental cell biology and nanomedicine.