Khalil Hassebi

Nicolas Rividi

Anne Verlaguet

Alexei Erko

Juergen Probst

Heike Loechel

Thomas Krist

Karine Le Guen

Philippe Jonnard

Detection of Li K Emission In Different Lithium Compounds

Methods:

Motivation:

Results:

Conclusion:

References:

3 Li X SQ 1. Excitation: The sample is being bombarded with and acccelerated beam of charged particles (electrons).

Ionization:

The interaction of the beam of electrons with matter leads to the ionization of the core states.

3. Emission: the vacancy is filled with an electron from an outer shell, resulting in the emission of an x-ray photon that correspond to the energy difference between the two states.

We demonstrate the possibility to spectroscopically analyze Li K emissions in different compounds using a non destructive and accessible technique. We also report for the first time the Li K emission bands in minerals. Our results unlocked potential for various applications to study in details the fine structure of valence band of lithium. ----------------------------------E Grating Law:

Electron Binding Energy

d(cos(α) -cos(β))= n Y e s !
Can we detect lithium and study its electronic structure in complex materials? How?

• Probing the fine electronic structure of the valence band using soft x-ray emission spectroscopy technique (SXES) integrated in EPMA • Tracking the changes in the chemical environment and emission spectrum (Intensity, shape, shift, band width...)

What?

You want to keep in touch!

Scan the QR code or contact me at: khalil.hassebi@sorbonne-universiter.fr [1] A. Erko et al., Opt. Express, vol. 22, no. 14, p. 16897, Jul. 2014, doi: 10.1364/OE.22.016897.

[2] K. Hassebi et al., X-Ray Spectrometry, doi: 10.1002/xrs.3329

The Li K emission occurs when a 2p valence states transition to 1s core states in lithium atoms and therefore the spectrum reflects the distribution of the p states within the valence band

Li K emission reported for the first time in minerals

Figure 2 :

 2 Figure 2: Wavelength dispersive spectroscopy (WDS) technique implemented inside the EPMA to acquire emission spectra

Figure 3 :

 3 Figure 3: Image of reflection zone plate spectrometer mounted on a eletron probe microanalyser (Cameca SX100).

•Figure 4 :Figure 1 :

 41 Figure 4: The Li K emission in LiF sample, presenting the emission band of Li metal and Li in oxide

  [2]. The Li K emission of lithium in LiF, Lepidolite K(Li,Al) 3 (Si, Al) 4 O 10 (OH) 2 , Bikitaite LiAlSi 2 O 6 (OH) 2 , and Amblygonite (Li,Na)Al PO (F,OH) is presented below.Incident angle αUnlock new frontier by allowing the quantification of lithium in complex materials such as lithium bearing minerals and materials used for lithium batteries with a technique that is both accessible and cost-effective.

Figure 5 :Figure 6 :

 56 Figure 5: The x-ray emission spectra of Lepidolite and Amblygonite in the full range of the spectrometer


Wael Karim

Agnès Petit

Eric Millon

Julien Vulliet

Malek Tabbal

Anne-Lise Thomann

Nadjib Semmar
email: nadjib.semmar@univ-orleans.fr

Nano-squares and regular LIPSS on YSZ coating by picosecond UV laser beam: thin film mediated and direct texturing

Keywords: Yttrium-stabilized zirconia, picosecond laser beam, Nano-structuring, LIPSS, Laser darkening

The laser texturing of high bandgap ceramic materials, such as Yttrium Stabilized Zirconia (YSZ), is very challenging due to their structural complexity, their mechanical fragility as well as the risk of a chemical decomposition under laser irradiation. The objective of this paper is to fabricate, in a controlled manner, well-organized nanostructures on microscale undulating YSZ coatings, and thus evaluate the feasibility to form laser-induced periodic surface structures (LIPSS), via two experimental approaches: the first one consists in laser structuring of YSZ through a mediated thin film (gadolinium doped ceria ~ 700 nm or Au ~20 nm), while the second one involves the direct structuring of the YSZ surface under static and scanning modes. A picosecond Nd: YAG laser (355 nm, 40 ps, 10 Hz) with a relatively large laser beam spot (~550 μm) was used. In the GDC and Au mediated texturing of YSZ under static conditions, we have observed nano-squares (~250 nm) and typical LIPSS perpendicular to the laser beam polarization, respectively. In the case of laser irradiation of the bare YSZ surface for fluences higher than 310 ± 10 mJ/cm 2 , LSFL and HSFL structures were formed depending on the number of pulses (from 10 2 to 10 3 ). The average spatial period measured for the thus-obtained HSFL is about 136 nm with an amplitude of 40 nm, as determined by Scanning Electron Microscopy (SEM) and Atomic Force Microscope (AFM). We have also demonstrated the ability to reproduce LIPSS on YSZ under scanning mode. A "darkening" phenomenon was observed on the YSZ surface at laser fluences exceeding 600 mJ/cm 2 , resulting from the formation of micro-spikes (with sizes close to 1 µm). XRD measurements demonstrated a slightly lower crystallinity of the laser irradiated YSZ material compared to the untreated YSZ surface.

Introduction

Ceramic oxide materials have several attractive properties such as good thermal resistance, high hardness values in addition to being, in many instances, chemically stable and biocompatible [START_REF] Komeya | High Temperature Engineering Ceramics, Book Chapter in Materials science and technology[END_REF]. They have been used in the aerospace and automotive industries [START_REF] González | Study of the high-temperature behaviour of nanostructured coatings produced by thermal spraying (combustion and plasma) from powders and suspensions[END_REF][START_REF] Sreedhar | Hot corrosion behaviour of plasma sprayed YSZ/Al2O3 dispersed NiCrAlY coatings on Inconel-718 superalloy[END_REF], as well as in the biomedical field [START_REF] Kirmizidis | Microfabricated Grooved Substrates Influence Cell-Cell Communication and Osteoblast Differentiation In Vitro[END_REF][START_REF] Lim | Cell Sensing and Response to Micro-and Nanostructured Surfaces Produced by Chemical and Topographic Patterning[END_REF]. Among such ceramics is the complex oxide yttrium-stabilized zirconia (YSZ) which is currently used as an electrolyte in solid oxide electrochemical cells (SOEC) for hydrogen production through high temperature electrolysis processes [START_REF] Hidalgo | Optimization of DC Reactive Magnetron Sputtering Deposition Process for Efficient YSZ Electrolyte Thin Film SOFC[END_REF][START_REF] Coddet | Multistep magnetron sputtering process and in-situ heat treatment to manufacture thick, fully oxidized and well crystallized YSZ films[END_REF][START_REF] Coddet | YSZ/GDC bilayer and gradient barrier layers deposited by reactive magnetron sputtering for solid oxide cells[END_REF]. For such applications, it is beneficial to increase the exchange surface area of the electrolyte /electrode interface. This can be done through the nano/micro-structuring of the surface of the YSZ electrolyte. Texturing of ceramic surfaces can be achieved through plasma etching [START_REF] Chambettaz | Characterization and development of a controlled sequential etching process at the nanoscale[END_REF] Computer Numerical Control (CNC) micromachining [START_REF] Holthaus | Comparison of micropatterning methods for ceramic surfaces[END_REF], or laser-based processes, such as thermal ablation and Direct Laser Interference Patterning (DLIP). One alternative laser-based approach is irradiation of the sample's surface slightly below the laser ablation threshold to form Laser Induced Periodic Structures (LIPSS) [START_REF] Bonse | Laser-Induced Periodic Surface Structures-A Scientific Evergreen[END_REF]. Such structures can be formed on different types of materials in a controlled manner and, under appropriate conditions, at nanoscale dimensions. As far as wide band-gap dielectric materials are concerned, it has indeed recently been shown that sub-picosecond laser beams could be used to obtain nanoscale LIPSS with periods depending on the wavelength "λ" of the laser beam. Dufft et al [START_REF] Dufft | Femtosecond laser-induced periodic surface structures revisited: A comparative study on ZnO[END_REF] detected on zinc oxide (ZnO) two types of LIPSS, Low Spatial Frequency (LSFL) LIPSS with a period Λ ≈ λ and High Spatial Frequency (HSFL) LIPSS with λ/2 < Λ < λ, by using a femto-second laser beam at 800 nm with laser fluence values ranging from 0.7 to 0.8 J/cm 2 (for LSFL) and from 0.5 to 0.7 J/cm 2 (for HSFL). On the other hand, Bashir et al [START_REF] Bashir | Femtosecond laser-induced subwavelength ripples on Al, Si, CaF2 and CR-39[END_REF] obtained HSFL structures, having a period of 70 nm on the surface of calcium fluoride (CaF2, a wide band-gap dielectric), by irradiation with a femto-second laser beam at 800 nm with a fluence of 0.5 J/cm 2 , a value that is very close to the ablation threshold of CaF2. Furthermore, the LSFL structures have been observed only on the metallic phase (Nb) of the composite alumina-zirconia-niobium Al2O3 -ZrO2 -Nb (78. 3 -1.7 -20 vol%), by means of a femto-second laser at 1025 nm [START_REF] Kunz | Selective generation of laserinduced periodic surface structures on Al2O3-ZrO2-Nb composites[END_REF], with a laser fluence of 0.4 J/cm 2 , which exceeds the ablation threshold of niobium (0.19 J/cm2) [START_REF] Mannion | The effect of damage accumulation behaviour on ablation thresholds and damage morphology in ultrafast laser micromachining of common metals in air[END_REF], while no chemical and morphological changes were detected on the surface of the ceramic material, since 0.4 J/cm 2 is well below the ablation threshold of Al2O3 (Fth = 5.62 J/cm 2 ) [START_REF] Filatova | Interpretation of the Changing the Band Gap of Al2O3 Depending on Its Crystalline Form: Connection with Different Local Symmetries[END_REF] , keeping in mind that the band-gap of Al2O3 is 7 eV [START_REF] Filatova | Interpretation of the Changing the Band Gap of Al2O3 Depending on Its Crystalline Form: Connection with Different Local Symmetries[END_REF].

Unlike metals and commonly used semiconductors, the absorption of a UV picosecond laser beam (355 nm) by wide bandgap materials, such as yttria-stabilized zirconia "YSZ" (Egap = 5,8 eV) [START_REF] Filatova | Interpretation of the Changing the Band Gap of Al2O3 Depending on Its Crystalline Form: Connection with Different Local Symmetries[END_REF], is less efficient compared to the femtosecond case, due to the transparent nature of the material and the limited multiphoton ionization and tunneling phenomena [START_REF] Florian | Controlling the Wettability of Steel Surfaces Processed with Femtosecond Laser Pulses[END_REF] at typical picosecond laser intensities (~10 9 W/cm 2 ). Thus, higher laser intensities are needed to work near the ablation threshold to induce LIPSS formation but simultaneously this would lead to enhanced damage formation in such fragile ceramic materials, and thus subsequently reduces the process window. To circumvent such limitations, it has been shown that the deposition of a thin metallic film on the substrate surface prior to laser structuring was beneficial either for lowering the threshold of LIPSS formation on dielectrics and semiconductors or to directly structuring the irradiated thin films by ultrashort beams [START_REF] Shavdina | Polystyrene Thin Films Nanostructuring by UV Femtosecond Laser Beam: From One Spot to Large Surface[END_REF][START_REF] Talbi | Comparative study of laser induced periodic surface structures formed on pulsed laser deposited and magnetron sputtered titanium oxide films[END_REF][START_REF] Talbi | Nanostructuring of titanium oxide thin film by UV femtosecond laser beam: from one spot to large surfaces[END_REF][START_REF] Huynh | Dependence of ablation threshold and LIPSS formation on copper thin films by accumulative UV picosecond laser shots[END_REF][START_REF] Huynh | Picosecond laser induced periodic surface structure on copper thin films[END_REF][START_REF] Talbi | Laser-induced periodic surface structures formation on mesoporous silicon from nanoparticles produced by picosecond and femtosecond laser shots[END_REF][START_REF] Talbi | Nanoparticles based laser-induced surface structures formation on mesoporous silicon by picosecond laser beam interaction[END_REF][START_REF] Huynh | In situ probing of pulsed laser melting and laser-induced periodic surface structures formation by dynamic reflectivity[END_REF][START_REF] Yin | Femtosecond laser-induced periodic surface structural formation on sapphire with nanolayered gold coating[END_REF][START_REF] Feng | Gold-film coating assisted femtosecond laser fabrication of large-area, uniform periodic surface structures[END_REF]. For example, Liu et al [START_REF] Liu | Deepsubwavelength ripples on the ZnO surface obtained via metal-film-assisted femtosecond laser processing[END_REF] have achieved HSFL fine structures (period ~100 nm) on the surface of ZnO assisted by aluminum film after femtosecond laser processing at 800 nm and 120 fs. The ablation threshold Fth was decreased by about 54%, compared to the uncoated pristine sample of ZnO. Clemens et al [START_REF] Kunz | Large-area Fabrication of Laser-Induced Periodic Surface Structures on Fused Silica Using Thin Gold Layers[END_REF] showed the generation of LIPSS on large areas of fused silica using a thin layer of gold and a femtosecond laser at 1025 nm with a pulse duration of 300 fs. The thin metal layer enhances the coupling of the laser beam with the underlying substrate through Surface Plasmons Polaritons (SPP) waves. As widely discussed in both theoretical and experimental works [START_REF] Dostovalov | The evidence of the role of surface plasmon polaritons in formation of femtosecond highly-regular laser-induced periodic structures on Cr films[END_REF][START_REF] Shuleiko | Femtosecond Laser Fabrication of Anisotropic Structures in Phosphorus-and Boron-Doped Amorphous Silicon Films[END_REF], the interference of the latter with the incident laser beam initiates LIPSS formation.

In the context of SOEC optimization, we previously investigated the laser texturing of a Gadolinium Doped Ceria (GDC) thin layer on the YSZ to enhance electrode surface area [START_REF] Karim | Picosecond laser beam nanostructuring of GDC thin films: exchange surface enhancement by LIPSS[END_REF]. The GDC layer was introduced as a diffusion barrier layer to inhibit the formation of undesired oxide phases that may be detrimental to the cell's performance [START_REF] Mickan | Optimized magnetron sputtering process for the deposition of gadolinia doped ceria layers with controlled structural properties[END_REF] In that work [START_REF] Karim | Picosecond laser beam nanostructuring of GDC thin films: exchange surface enhancement by LIPSS[END_REF], a UV picosecond beam was utilized and LIPSS pattern on GDC were formed depending on laser dose (defined as the laser fluence times the number of pulses, FxN). It was also reported that, at high laser doses, ablation of the entire GDC film can take place leaving a textured YSZ substrate, in the form of nano-squared structures. Based on this finding, the present paper is dedicated to the investigation of the texturing of YSZ using the same UV laser beam under various configurations. First, we will consider the laser irradiation of the YSZ surface coated by the GDC layer, as is the case in a real SOEC. Then, we will investigate the effect of the presence of a metal coating, namely Au, on the laser irradiation of YSZ. Finally, we will compare the results of these experiments with the laser structuring of the bare YSZ surface under both static and scanning mode configurations. At last, we explore the effect of increasing the laser dose leading to the formation of nano and micro spikes.

Experimental

The YSZ substrates, (ZrO2)0.92 (Y2O3)0.08, provided by the 'Commissariat de l'Energie Atomique' (CEA), have thicknesses of about 8 μm and were deposited by screen-printing on a porous Ni-YSZ cermet, as shown in the Figure 1. This led to a somewhat undulating YSZ surface at the microscale (a few microns).

Approximately 700 nm thick GDC thin films were deposited by pulsed direct current magnetron sputtering from a 4-inch diameter of Ce1-xGdx metal target onto the YSZ substrates. All deposition runs were performed at room temperature at a pressure of 1 Pa with 20 sccm Ar as sputtering gas, 2 sccm and O2 as a reactive gas. The as-deposited films were then annealed in air at 500 °C, a process that resulted in highly crystalline and stoichiometric layers (Ce1-xGdxO2). More details on the growth conditions and properties of the films have been presented elsewhere by Mickan et al [START_REF] Mickan | Optimized magnetron sputtering process for the deposition of gadolinia doped ceria layers with controlled structural properties[END_REF]. On the other hand, the Au thin films have a thickness of ~20 nm and were deposited on YSZ by plasma sputtering from a 2-inch gold target at a pressure of 0.5 Pa with 20 sccm Ar as sputtering gas. All irradiation experiments were performed using a picosecond Nd: YAG laser operating at its third harmonic (λ = 355 nm) with a pulse duration of 40 ps and a repetition rate of 10 Hz [START_REF] Karim | Picosecond laser beam nanostructuring of GDC thin films: exchange surface enhancement by LIPSS[END_REF],. The energy/pulse is modulated using an optical filter energy (Thorlabs UGC), and the laser Gaussian beam is focused to a 550 µm diameter spot on the sample's surface using a quartz lens with a focal length of 75 mm. The samples were irradiated in static mode (by accumulation of successive shots) or in scanning mode in ambient air as shown in Figure 2. In static mode, the total number of shots (N) irradiating the same area of the sample is controlled by synchronized beam chopper. In scanning mode, which is necessary for large area irradiation, the sample is mounted on a motorized and computer-controlled X, Y scanning stage. To irradiate the entire film surface, an S-shaped scanning pattern of the sample is realized via a LabVIEW interface. Using an automated scanning system (Newport-Conex CC scanner with an accessible speed ranging from 0.001 to 5 mm/s in the X, Y directions, with a translation path ΔY = 100 μm), the sample is moved along the X-axis at a speed Vx and displaced by a distance ΔY (perpendicular to the X-axis) at the end of the movement. For the present study, the laser fluence (F) and the pulse number (N) were typically varied from 125 to 375 mJ/cm 2 , and from 10 to 1000 shots, respectively. In instances where a higher laser dose was needed, F and N were increased to 625 mJ/cm 2 and 20000, respectively. The values of Vx used in this work were varied from 6 μm/s up to 100 µm/s. The surface morphology of the thin films before and after laser irradiation was examined using a Carl Zeiss SMT SUPRA 40 very high resolution field emission gun scanning electron microscope (SEM). The amplitude and periodicity of the LIPSS patterns were determined using a atomic force microscope (AFM). AFM images were collected using a Bruker Dimension Icon in ScanAsyst air mode. The structural characterization were carried out by X-ray diffraction (XRD) in the Bragg-Brentano  geometry using a Bruker D8 Discover system with Cu Kα radiation (0.15406 nm).

Results and Discussion

Thin film-mediated structuring of YSZ

In this section, we will first report on the laser structuring (in static mode) of the YSZ material coated with the GDC barrier layer, then compare these results with laser irradiation of YSZ coated with a thin 20 nm Au film. Figure 3 shows SEM images of GDC/YSZ samples irradiated at different laser fluences and number of pulses. For low doses (F=125 ± 10 mJ/cm 2 , N=50, Fig. 3.a), the sample's surface shows regularly arranged YSZ square shaped patterns or nano-squares (NS). These patterns are similar to the YSZ nano-squares observed at comparable laser doses reported in our previous work, where it was shown that this results from a complete ablation of the GDC film, as confirmed by Electron Dispersion X-Ray (EDX) analyses [START_REF] Karim | Picosecond laser beam nanostructuring of GDC thin films: exchange surface enhancement by LIPSS[END_REF]. These nanosquares are observed across the entire laser beam impact. Their size is close to the wavelength used at 355 nm, and their orientation is uniform within an YSZ grain but varies across grain boundaries. However, at higher laser doses (F = 310 ± 10 mJ/cm 2 , N = 1000, Fig. At the center of the beam, periodic ripples are observed on the YSZ substrate with a spatial period close to 110±10 nm which is smaller than half the laser wavelength (λ/2). These ripples are thus identified as HSFL [START_REF] Filatova | Interpretation of the Changing the Band Gap of Al2O3 Depending on Its Crystalline Form: Connection with Different Local Symmetries[END_REF][START_REF] Das | Multiphoton excitation of surface plasmon-polaritons and scaling of nanoripple formation in large bandgap materials[END_REF][START_REF] Jia | Formation of nanogratings on the surface of a ZnSe crystal irradiated by femtosecond laser pulses[END_REF], oriented perpendicular to the E polarization of laser beam and are located at the center of laser spot i.e., in the regions where the laser energy/fluence is highest (FCenter = 215 mJ/cm 2 ).

AFM analyses were also performed on the CDG/YSZ laser irradiated samples as presented in Figure 4, for the samples corresponding to those imaged in Fig. 3. Figure 4.a corresponds to the sample irradiated with a low dose (F = 125 mJ/cm 2 and N = 50) and confirms the formation of nano-squared structures with typical side length of ~250 nm (in fair agreement with the SEM image, Fig. 3.a) with a depth amplitude varying between 20 and 40 nm. However, if we compare their shapes with that obtained at high energy dose (Fig. 4.b, F = 310 mJ/cm 2 and N = 1000), we can notice that the size of the latter is somewhat smaller (220-230 nm) with a slightly greater depth amplitude of about 50 nm. At the higher dose, some re-deposition is observed at the surface appearing as dispersed white spots in Fig. 4.b. The effect observed at the higher laser dose could be explained by the injection of photonic energy in the CDG/YSZ system. The NS that appear on the YSZ surface after the complete ablation of GDC, can be a result of surface micro-cracking or fragmentation. It is generally accepted that these types of morphologies occur because of thermo-elastic stresses induced by the heating of the laser irradiated volume of the material [START_REF] Mannion | The effect of damage accumulation behaviour on ablation thresholds and damage morphology in ultrafast laser micromachining of common metals in air[END_REF][START_REF] Das | Multiphoton excitation of surface plasmon-polaritons and scaling of nanoripple formation in large bandgap materials[END_REF]. Indeed, such structures were also observed by Talbi et al. in 1D patterns on the surface of TiO1.8 irradiated by a femto-second laser, when the laser fluence exceeds a damage threshold related to the cracking phenomenon before the melting phase [START_REF] Talbi | Femtosecond laser irradiation of titanium oxide thin films: accumulation effect under IR beam[END_REF]. Finally, the HSFL structures (spatial period close to 130 nm) formed under the high laser energy dose conditions (see Figure 3.b2) are attributed to a selforganization mechanism resulting from thermo-capillary and hydrodynamic instabilities as recently reported in the literature [START_REF] Jia | Formation of nanogratings on the surface of a ZnSe crystal irradiated by femtosecond laser pulses[END_REF].

For comparative reasons, we have performed laser irradiation on the YSZ samples coated with a metallic gold thin film of 20 nm. For a laser fluence (F = 250 mJ/cm 2 ), we vary the number of pulses from 1 to 1000 shots. Firstly, strong ablation occurs for the Au/YSZ film at the first laser shot as shown by the nanometric particles dispersed on the surface (Figure 5.a). By increasing N up to 10 pulses, most of the gold nanoparticles are removed from the surface with some cracking and melting of the surface occurring (Figure 5.b). At N=100 shots (Fig. 5.c), LIPSS formation is initiated, and those become well organized and resolved for N =1000 shots (Fig. 5.d). These ripples are LSFL-like, perpendicular to the E polarization with a spatial period close to 250 nm. We propose that the presence of the thin metallic film (Au) on the surface of YSZ, has contributed to enhance the excitation of the surface plasmon polaritons (SPPs) surface waves to interfere with the incident laser beam, as supported by the Sipe electromagnetic model for LSFL formation [START_REF] Rivera | Subwavelength LIPSS formation on SS304 by picosecond laser irradiation under water confinement[END_REF][START_REF] Zhao | Investigation of laser ablation features of molybdenum bulk for picosecond laser-based techniques in fusion devices[END_REF][START_REF] Senegačnik | Influence of processing parameters on characteristics of laser-induced periodic surface structures on steel and titanium[END_REF]. This excitation enhances the regularity of LIPSS formation on YSZ. It is noteworthy that we did not detect the appearance of NS structures for gold coated YSZ, as was the case for the GDC/YSZ system. Indeed, the GDC dielectric layer is transparent at the wavelength used (355 nm), and therefore the laser photons will attack the surface of the YSZ substrate since the first laser pulse, which may explain the appearance of NS on YSZ just after complete removal of GDC. On the other hand, the mediated gold metallic layer will absorb the maximum laser photons.

Laser structuring of bare YSZ surfaces

Figure 6 shows SEM images of different morphologies at different location of the bare YSZ surface, irradiated under static mode conditions with 500 shots at a fluence of 310 mJ/cm 2 . Compared to the fluence F = 250 mJ/cm 2 applied to the YSZ surface assisted by a gold thin film, necessary for LIPSS formation, the fluence value used in the case of direct texturing on YSZ was increased by about 20%. Indeed, Wen et al [START_REF] Wen | Improvement of ablation capacity of sapphire by gold film-assisted femtosecond laser processing[END_REF] reported that the threshold fluence of uncoated sapphire was 56% greater compared to Au-coated sapphire. Figure 6 shows three different laser-matter interaction areas, depending on the Gaussian distribution of laser beam (indicated by the dotted red line):

Zone I: The central ablation region that receives the highest amount of energy (peak intensity), showing a hole resulting from the ablation of the YSZ material, with the formation of micro-spikes at the hole boundary.

Zone II: Moving from the center to the edges, the intensity of the laser beam gradually decreases, we can assume that fusion of YSZ occurred with a texturing of the surface to form LIPSS (LSFL).

Zone III: At the edges of the laser impact, the lower energy density generates local changes through annealing of the YSZ substrate. This surface heating modifies the topography of the YSZ surface with the formation of less resolved LSFL. In order to investigate the LIPSS formation domain directly on YSZ in static mode, the number of laser shots was varied between 100 and 1000 shots for two fluence values, 310 and 375 mJ/cm 2 . For F = 310 mJ/cm 2 , non-regular structures start to form on the YSZ surface, following the onset of local YSZ melting (Figure 7.a), but LSFL-like LIPSS are observed for 750 laser shots (Figure 7.b) with some local bifurcations appearing at the grain boundaries observed on the untreated YSZ sample. The large scale (micrometric) roughness of the YSZ grain morphology is preserved after laser texturing.

By increasing N up to 1000, we can observe poorly organized HSFL structures, also perpendicular to the polarization E (Figure 7.c). Indeed, L. Parellada-Monreal et al [START_REF] Parellada-Monreal | Laser-induced periodic surface structures on ZnO thin film for high response NO2 detection[END_REF] reported HSFL textures of period 145 nm with an amplitude of about 100 nm, on a zinc oxide (ZnO) sample using a femto-second laser at 800 nm. On the other hand, if we increase F up to 375 mJ/cm 2 , the formation of LSFLs starts rather after 100 shots. This confirms that the key parameter for LIPSS formation is the applied energy density (F) (Figure 7 In the case of a number of pulses N = 20000 at the same laser fluence (F = 310 mJ/cm 2 ), elongated nano-spikes structures appear on top of the LSFL already formed on the YSZ surface, both of which are perpendicular to the polarization of the E laser beam, as shown in the figure 8. Based on SEM images, the size of these Nano-Spikes is found to vary between 0.8 and 1 µm (Figure 8.a), while the approximate spatial period of LSFLs is about 240 nm (Figure 8.b) [START_REF] Semmar | Microspikes formed on mesoporous silicon by UV picosecond laser irradiation[END_REF].

The energy of a picosecond laser photon at 355 nm is 3.5 eV, which is much lower than the value of the YSZ band gap (5.8 eV), so it excludes the phenomenon of photoionization. Therefore, the YSZ substrate will not be ionized under the effect of few pulses laser regime, which explains the formation of LSFL for N>100, as a result of laser shots accumulation effects [START_REF] Nakhoul | Self-Organization Regimes Induced by Ultrafast Laser on Surfaces in the Tens of Nanometer Scales[END_REF].

Large surface LIPSS formation on the YSZ substrate was investigated under scanning mode conditions for a laser fluence of 310 mJ/cm 2 at different scanning speed from 30 to 6 μm/s. For example, for a velocity of 6 μm/s, the effective number of pulses " Neff ", which is of the order of 4500 shots, is well outside the range of pulse values applied in the static mode (100 < N < 1000).

Table-1:

Neff versus scanning speed VX applied for YSZ layer processing. In Table 1, we report the different values of pulses NX, NY and Neff, for each scanning speed VX. It can be noted that, the lower speed, the higher effective number, or in other words, the longer irradiation time of the laser beam. The objective is to structure a square of 4x4 mm 2 . The effective number Neff ≈ 900 shots, which corresponds to the velocity VX = 30 µm/s, is likely to be almost correlated with what was observed in static mode for F = 310 mJ/cm 2 and N = 750 shots (see Figure 7.b). With this condition shown in Figure 9.a, we observe periodic structures (LIPSS) on the YSZ surface. Going to a scanning speed of VX = 20 μm/s (Neff ≈ 1375), these ripples would become more regular since the energy dose absorbed by the YSZ surface increased with the lowering of the velocity. For VX = 15 μm/s (Figure 9.c), material ablation due to the intense laser beam becomes more severe. On the other hand, an excessive decrease in scanning speed, accompanied by a significant rise in the YSZ surface temperature that exceeds the boiling temperature of YSZ, can lead to a phenomenon of complete evaporation of YSZ layer (thickness 8 μm). Thus, we managed to find a range of parameters (F and VX), to reproduce LIPSS in scanning mode to structure large-scale surfaces up to several mm2.

Fig. 9 SEM images showing the scanning conditions applied on the YSZ surface for F = 310 mJ/cm 2 .

An interesting phenomenon has been observed, when we irradiated YSZ with the picosecond laser beam at relatively higher fluences, F = 625 mJ/cm 2 , and VX = 0,1 mm/s, is a darkening (or blackening) effect [44] [45] as observed at the macroscopic scale on our sample i.e. the green surface color of YSZ is transformed into dark gray (Figure 10.a). According to Pereira et al. [START_REF] Pereira | Influence of laser texturing on surface features, mechanical properties and low-temperature degradation behavior of 3Y-TZP[END_REF] and the work of Guo et al [START_REF] Guo | Darkening of zirconia: a problem arising from oxygen sensors in practice[END_REF] this darkening effect could also be due to the loss of oxygen on the surface during laser irradiation. On the other hand, this color variation has been noticed by Pereira [START_REF] Pereira | Influence of laser texturing on surface features, mechanical properties and low-temperature degradation behavior of 3Y-TZP[END_REF] for several lasers textured YSZ samples (micro-grains, micro-cracks, etc.) for fluence ranging from 212 to 424 J/cm 2 and scanning speeds varying between 15 and 50 mm/s. On the cross-sectional SEM image of the textured YSZ (Figure 11), we can see that about half of YSZ thickness is ablated from the adjacent Ni-YSZ surface, confirming that the ablation threshold is reached at the high laser fluences leading to spike formation. Actually, the surface temperature increased to the evaporation temperature of the YSZ which explains the partial removal of the surface. The FWHM of the diffraction peaks is larger for the (111) YSZ peak, the FWHM is 0.166° which correspond to an average crystallite size of about 50 nm. Therefore, the darkening effect induced a lower YSZ crystallinity, i.e. a kind of disorder of the material. The position of the YSZ peaks is significantly shifted towards high angles. Indeed, the peak (111) is slightly shifted from 29.99° (before laser structuring) to 30.08° (after treatment), and the laser texturing induces a decrease of the lattice parameter of YSZ. Therefore, to maintain the microstructure of the YSZ required for the application, we should use laser fluences well below 625 mJ/cm 2 .

Conclusion

In this paper, we report on the fabrication of regular nanostructures on YSZ coatings and the feasibility to form LIPSS on microscale undulating YSZ surface via two experimental approaches: the first one consists in laser structuring of YSZ mediated through a thin film (dielectric "GDC" or metallic "Au"), while the second involves the direct structuring of a bare YSZ surface under static and scanning modes. The purpose of comparing the two laser structuring methods is to investigate the most regular LIPSS morphology that gives us a better increase in the specific surface area of the YSZ electrolyte exchange surface in solid oxide electrolyte cell (SOEC) applications. On the other hand, the formation of new structures like Nano-squares (NS) on YSZ by means of GDC thin film, can significantly increase the specific surface based on the geometrical model mentioned in our previous article cited in ref. [START_REF] Karim | Picosecond laser beam nanostructuring of GDC thin films: exchange surface enhancement by LIPSS[END_REF].

Firstly, in the mediated texturing of YSZ through a GDC oxide thin film, we have observed nanosquares structures on the YSZ surface after the complete ablation of GDC, under static mode for F = 310 mJ/cm 2 , N = 1000 at the edges of laser spot (FEdges = 150 mJ/cm 2 ). These NS (with a size of 250x250 nm 2 ) resulted from thermo-elastic stresses induced by laser irradiation. Other HSFL structures, perpendicular to laser polarization, are observed at the center of the laser spot, and attributed to selforganization phenomena due to the accumulation effect of a high number of shots (N = 1000). These structures have a spatial period of about 120 nm. Uniform LSFL perpendicular to the laser beam polarization were formed on the YSZ substrate due to the excitation of the surface plasmon polaritons (SPP) waves. In the second part of the work, namely the case of laser irradiation of the bare YSZ surface, LSFL and HSFL structures were observed with an average spatial period measured for the thus-obtained HSFL is ~ 140 nm with an amplitude of 40 nm. We have also succeeded in reproducing LSFL on YSZ under scanning mode. Then, we have detected a darkening effect on YSZ samples, where micro-spikes microstructures are formed (size ~ 1 µm) for fluences exceeding 600 mJ/cm 2 . Finally, XRD measurements demonstrated a slightly lower crystallinity of the laser irradiated YSZ material compared to the untreated YSZ surface.

List of Figures

Fig. 1

 1 Fig.1 Scanning Electron Microscope image showing the transverse section of the YSZ substrate.

Fig. 2

 2 Fig.2 Schematics of mediated (a) and direct (b) structuring approaches for YSZ material.

  3.b), and within a single impact of the Gaussian laser beam, two different regions (Figs. 3.b1 and 3.b2) can be distinguished corresponding to the formation of two types of nanostructures. In order to estimate the fluence values between the edges and the center of the laser pattern, we have used the following an exponential function: F(d) = F0 e -(d/D) , with F0: Peak fluence at the point center; d: Beam of the zone concerned; D: laser spot beam ≈ 550 µm.

Figure 3 .

 3 Figure 3.b1 shows NS on YSZ substrate at the edge of laser spot that corresponds to the low intensity regions of the Gaussian beam (FEdges = 150 mJ/cm 2 ), in agreement with the low dose case presented in Fig. 3.a.

Fig. 3

 3 Fig.3 SEM images showing the comparison of the indirect texturing of YSZ at F = 125 mJ/cm 2 and N = 50 (a) and F = 310 mJ/cm 2 and N = 1000 (b) laser energy dose. The green box (b1) corresponds to the edges (FEdges = 150 mJ/cm 2 ) and the red box (b2) corresponds to the center (FCenter ≈ 215 mJ/cm 2 ) of laser spot presented in (b).

Fig. 4

 4 Fig.4 AFM height images (size 2x2 µm 2 size) show the topography of YSZ substrate after GDC ablation at low and high energy doses that's correspond: (a) Fig.3-a at F = 125 mJ/cm 2 and N = 50; (b) Fig.3-b1 and (c, d, e) Fig.3-b2 for F = 310 mJ/cm 2 and N = 1000; (e) shows the evolution of the period and amplitude of HSFL structures generated along a measurement profile.Furthermore, Figure4.c represents the AFM analysis of the periodic structures identified as HSFL in Fig.3.b2, which are formed in the center of the high fluence laser region within the laser spot (high laser dose conditions, F = 310 mJ/cm 2 , N=1000). A 3D view AFM image for this same irradiation condition is shown in Figure4.d, which allows to visualize the profile of these ripples, a plot of which is presented

Figure 4 .

 4 Figure 4.e. This latter figure shows that the average spatial period of the LIPSS is about 130 nm, close to the third of the laser wavelength (λ/3), in agreement with the SEM image presented in Figure 3.b2,

Fig. 5

 5 Fig.5 SEM images showing the evolution of Au/YSZ surface morphology as a function of N, for F = 250 mJ/cm 2 .

Fig. 6

 6 Fig.6 SEM image showing the three regions of the laser pattern formed on YSZ surface in static mode for F = 310 mJ/cm 2 and N = 500: the white circle (ablation); the green box (melting); the red box (annealing); the black box (untreated sample of YSZ); as well as the yellow box showing the laser spot pattern on which we see the dotted line of the Gaussian profile of the picosecond laser beam of diameter 550 µm.

  .d). The formation of HSFL occurs likewise when the number N of pulses increases from 750 to 1000 pulses (Figures. 7.

  e and 7.f).

Fig. 7

 7 Fig.7 SEM image showing the LIPSS formation in static mode by varying the number of pulses from 100 to 1000 for two fluences F = 310 (a-c) and 375 mJ/cm 2 (d-f). (g) AFM height image (5 x 5 µm 2 size) for the HSFL condition presented in (f), and (h) showing the period and amplitude evolution of the generated LIPSS along a measurement profile (orange line).

Figure 7 .

 7 Figure 7.g shows an AFM image of the surface topography in static mode after laser irradiation of 1000 pulses at a fluence of 375 mJ/cm 2 . The profile analysis confirms that the average spatial period of the LIPSS formed is about 136 nm (Fig. 7.h), in agreement with the SEM image presented in Fig.7.f and an amplitude of about 40 nm.

Fig. 8

 8 Fig.8 SEM images showing the LIPSS formation in static for F = 310 mJ/cm 2 and N = 20000. (b) represents the magnification (x3) of the SEM image presented in (a).

*

  NX Effective number of pulses in X direction ** NY Effective number of pulses in Y direction

Fig. 10 (

 10 Fig. 10 (a) The blackening effect on the YSZ patterned by the picosecond laser beam at 355 nm, F = 625 mJ/cm 2 and VX = 0,1 mm/s, (b) SEM image showing the appearance of micro-spikes upon the ablated YSZ surface and (c) the magnification (x2) of the SEM image presented in (b). The black squares (A and B) indicate the two DRX measurement points for the untreated and treated area of YSZ respectively.

Fig. 11

 11 Fig.11 SEM image showing the cross section of YSZ material after laser texturing at F = 625 mJ/cm 2 , VX = 0.1 mm/s and ΔY = 0,1 mm.

Fig. 12 X

 12 Fig.12 X-Ray Diffractometry on the YSZ film for both areas: untreated zone (a) and textured zone (b). Y0.15Zr0.85O1.93 (8YSZ) material was retrieved from the database JCPDS file# 00-030-1468, and NiO from the database file# 00-047-1049.

Figure 1 :

 1 Figure 1: SEM image showing the transverse section of the untreated YSZ material.

Figure 2 :

 2 Figure 2: Schematics of indirect (a) and direct (b) structuring approaches for YSZ material.

Figure 3 :

 3 Figure 3: SEM images showing the comparison of the indirect texturing of YSZ at F = 125 mJ/cm 2 and N = 50 (a) and F = 310 mJ/cm 2 and N = 1000 (b) laser energy dose. The green box (b1) corresponds to the edges and the red box (b2) corresponds to the center of laser spot presented in (b).

Figure 4 :

 4 Figure 4: AFM images show the topography of YSZ substrate after GDC ablation at low and high energy doses that's correspond: (a) Fig.3-a at F = 125 mJ/cm 2 and N = 50; (b) Fig.3-b1 and (c, d, e) Fig.3-b2 for F = 310 mJ/cm 2 and N = 1000; (e) shows the evolution of the period and amplitude of HSFL structures generated along a measurement profile.

Figure 5 :

 5 Figure 5: SEM images showing the evolution of Au/YSZ surface morphology as a function of N, for F = 250 mJ/cm 2 .

Figure 6 :

 6 Figure 6: SEM image showing the three regions of the laser pattern formed on YSZ surface in static mode for F = 310 mJ/cm 2 and N = 500: the white circle (ablation); the green box (melting); the red box (annealing); the black box (untreated sample of YSZ); as well as the yellow box showing the laser spot pattern on which we see the dotted line of the Gaussian profile of the picosecond laser beam of diameter 550 µm.

Figure 7 :

 7 Figure 7: SEM image showing the LIPSS formation in static mode by varying the number of pulses from 100 to 1000 for two fluences F = 310 (a-c) and 375 mJ/cm 2 (d-f). (g) AFM image for the HSFL condition presented in (f), and (h) showing the period and amplitude evolution of the generated LIPSS along a measurement profile (orange line).

Figure 8 :

 8 Figure 8: SEM images showing the LIPSS formation in static for F = 310 mJ/cm 2 and N = 20000. (b) represents the magnification (x3) of the SEM image presented in (a).

Figure 9 :

 9 Figure 9: SEM images showing the scanning conditions applied on the YSZ surface for F = 310 mJ/cm 2 by using the picosecond laser beam at 355 nm (f=10 Hz).

Figure 10 :

 10 Figure 10: (a) The blackening effect on the YSZ patterned by the picosecond laser beam at 355 nm at F = 625 mJ/cm 2 and VX = 0,1 mm/s, (b) SEM image showing the appearance of microspikes upon the ab-lated YSZ surface and (c) the magnification (x2) of the SEM image presented in (a). The two small black squares (A and B) indicate the two DRX measurement points for the untreated and treated area of YSZ respectively.

Figure 11 :

 11 Figure 11: SEM image showing the cross section of YSZ material after laser texturing for F =

Acknowledgments:

The authors would like to thank the French 'Region Centre-Val-de-Loire' for funding via the 'ARD Lavoisier' and 'ARD MATEX' programs.

625 mJ/cm 2 , VX=0.1mm/s and ΔY=0,1 mm. Figure 12: X-Ray Diffractometry on the YSZ film for both areas: untreated zone (a) and textured zone (b).

Conflicts of Interest:

The authors declare no conflict of interest concerning this work. Table 1: Neff versus scanning speed VX applied for YSZ layer processing

List of Tables


Hannah Soudry

Christophe Desmarets
email: christophe.desmarets@upmc.fr

Geoffrey Gontard

Tiffany Edgington

Andrew L Cooksy

Hani Amouri
email: hani.amouri@upmc.fr

Chiral Two Bladed ML 2 Metallamacrocycles: Design, Structures and Solution Behavior

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Another interesting challenge is to be able to control the stereochemistry of the final nanostructure. 3 The use of an optically active ligand to assure chiral transfer to the metal centre is the most appropriate approach; however it is tedious and requires the preparation of the optically active ligands beforehand. 4 However chirality can also arise at the metal centre using achiral bidentate ligands; for instance helicoïdal chirality ( or  ) in octahedral metal complexes arises upon coordination of the metal centre by at least two achiral bidentate ligands. 4 A more convenient approach consists in the preparation of racemic molecules or metallacycles followed by separation using chiral auxiliaries to obtain the target optically active supramolecules.

In this context, our group has developed the use of 1,3-(bis(benzimidazol-1-ylmethyl)-2,5-dimethoxy-4,6 dimethylbenzene to construct a variety of appealing supramolecular structures such as coordination polymers, metallamacrocycles, and cages. 5 We have established the synthesis of some discrete self-assembled metallasupramolecular 3D capsules of type M 2 L 4 based on Co(II) and Cu(II) that are able to encapsulate weakly coordinated anions such as BF 4 -and PF 6 -. More recently, the introduction of a highly rigid luminescent ligand in our systems leads to the formation of silver polymers and Pd 2 L 4 luminescent nanocapsules capable of accommodating neutral organic molecules and/or anionic organometallic complexes as guests. 6 As part of our research program, we sought to introduce a chiral spacer ligand in our systems to design and prepare new metallasupramolecular assemblies in which internal cavities could be used for enantioselective recognition and separation of small molecules. The present work describes our preliminary results using this novel chiral assembling ligand to construct chiral coordination assemblies.

Herein we describe the formation of homochiral two bladed ML 2 metallamacrocycles (M = Co(II), Zn(II)) but obtained as racemates R,R /S,S in 50/50 ratio starting from racemic ligand and the metal salts. No meso-complexes were obtained, illustrating a ligand sorting mechanism. Conversion of this racemic material to a mixture of diastereoisomeric salts using chiral anion metathesis is also reported. The semi-rigid bidentate assembling ligand L contains two peripheral methyl benzimidazole moieties connected to 5,5',6,6'-tetramethyl-2,2'-dimethoxy-1,1'-biphenyl as a central spacer. 7 Ligand L displays intrinsic C2 symmetry and was prepared in good yield (Scheme 1) by nucleophilic substitution 5f of the known compound 3,3'-bis(chloromethyl)-2,2-dimethoxy-5,5',6,6'tetramethyl-1,1'-biphenyl and was fully characterized by IR, NMR and elemental analysis. Treatment of L (2 equiv) with Co(II)(BF 4 ) 2 .6H 2 O in CH 3 CN solution gave immediately a violet solution. After 12h of reaction the solution was concentrated and yielded a purple solid material that was isolated quantitatively and analysed elementally as [Co(L) 2 (BF 4 ) 2 ](1) (Scheme 2). Interestingly, this result contrasts with those obtained previously by our group where M 2 L 4 metallacages were obtained when the achiral semi-rigid bis(benzimidazole) ligand was employed.

The latter lacks the chiral spacer 5,5',6,6'-tetramethyl-2,2'dimethoxy-1,1'-biphenyl but instead the two benzimidazole arms are attached to a central arene. + species in solution. Due to the paramagnetic nature of the cobalt complex 1 the 1 H NMR spectrum was not informative. To ascertain the identity of complex 1, convenient crystals for Xray structural determination were prepared from CH 3 CN/Et 2 O solution after several attempts. The compound crystallized in the monoclinic space group C2/c. The structure shows the formation of a CoL 2 dicationic complex (Figure 1) where the cobalt centre adopts a pseudotetrahedral geometry; each position is filled by a benzimidazole from the two bridging ligands L. The Co---N bond lengths lie in the range of 2.00-1.98(2) Å typical to those reported in the literature. 5 Interestingly, the X-ray structural determination reveals the formation of a racemic mixture of homochiral complexes (R, R)-[Co((R ax )-L) 2 (BF 4 ) 2 ](1) and (S,S)-[Co((S ax )-L) 2 (BF 4 ) 2 ](1) (Figure 1). Hence the heterochiral (R, S) complex was not formed. A self sorting ligand recognition process mediated by the cobalt(II) metal centre seems to operate and hence favours the formation of the homochiral compound. To ascertain the molecular structure of 2, an X-ray structural determination was carried out. Crystals of 2 were grown by vapor diffusion of diethyl ether into a solution of the complex in CH 3 CN. Compound 2 turned out to be isostrucural to 1 and exhibited a similar distorted tetrahedral geometry around the metal centre. The Zn---N bond lengths lies in the range of 1.99-2.00Å (Figure 3).

M(BF 4 ) 2 2 2 + 2(BF 4 - ) CH 3 CN L N M N N N ML 2 2+
Please do not adjust margins Please do not adjust margins We then examined the solution behavior of this chiral two bladed complex 2 and its differentiation using a chiral auxiliary anion. 8 To attain this objective, the racemic mixture The infrared spectrum of the resulting material confirmed the disappearance of the bands of BF 4 anions at 1053 cm -1 and the presence of novel bands at 989 cm -1 and 669 cm -1 that we attribute to -TRISPHAT. Moreover the 31 P NMR spectrum recorded in CD 3 CN showed a singlet at -81.1 ppm assigned to -TRISPHAT as reported in the literature. 8f The Unfortunately all our attempts either by chromatography or fractional crystallization to separate both diastereoisomers were not successful.

At this stage a comment on the homochiralty issue in these metallamacrocycles is required. For instance Wang et al. have demonstrated in an elegant work the formation of 3D homochiral polyhedra with rotational faces. 9 The authors show that the polyhedra self assemble from four truxene-based building blocks acting as faces and six diamine units that form the vertices. Depending on the rotational sense in which the -C=N-linkages are bent the truxene turns clockwise or anticlockwise and therefore the assembly becomes homochiral.

Their studies on the kinetics and mechanism revealed that the This journal is © The Royal Society of Chemistry 20xx

Please do not adjust margins Please do not adjust margins non-covalent interaction among the faces is essential to the facial homochirality. Thus we then studied the kinetic formation of 2 by adding a sequential amount of ligand L to Zn(BF 4 ) 2 in CD 3 CN and monitored the formation of the assembly by A computational investigation 10a of the complex supports a small but consistent thermodynamic preference for the observed enantiopure diastereomer over the racemic form. Initially, because experiments had not confirmed the spin of the organometallic complex, we optimized geometries of (1) with doublet, quartet, and sextet multiplicities using the B3LYP density functional method 10b and a small 3-21G(H,C,N,O),LANL2DZ(Co) basis set, 10c confirming that the quartet state is significantly (>28 kcal/mol) more stable than the others, as expected. The geometries were then reoptimized with a larger cc-pVDZ(C,H,N,O),CEP-121G(Co) basis set, 10d and vibrational frequencies were calculated in order to obtain the free energy corrections. For both basis sets, the free energy of the enantiopure form at 298 K lies only 1.0 to 1.1 kcal/mol below the R,S free energy. However, additional corrections for solvation (using COSMO or IEFPCM methods 10e )

and for dispersion forces (Grimme's GD2 method 10f

) using the larger basis set increase this free energy gap to 3.7 kcal/mol. This difference would cause a measurable preference for the enantiopure diastereomer in experiments, but is not much greater than the expected error in these methods. This predicted free energy difference is also smaller than the 12 kcal/mol gap found for the similar system investigated by Wang et al.,9 which suggests that the enantioselectivity of the present case may arise from kinetic as well as thermodynamic considerations.

Conclusions

In this communication, we reported the efficient preparation and characterization of chiral two bladed dicationic complexes [Co(L) 2 ][BF 4 ] 2 (1) and [Zn(L) 2 ][BF 4 ] 2 (2). Interestingly, due to a ligand self-sorting process the formation of homochiral chiral metallacages is favoured to give H-NMR analysis. Our future objectives will be devoted to separate the diastereomers as well as to prepare optically active Co(II) and Zn(II) complexes starting from the enantiopure form of ligand L .

(R,R)-[M(L) 2 ][BF 4 ] 2 M = Co, ( 1a

Experimental Section

General experimental methods

All solvents used were reagent grade or better. Commercially available reagents were used as received. 3,3'-bis(chloromethyl)-2,2-dimethoxy-5,5',6,6'tetramethyl-1,1'-biphenyl

Synthesis

Ligand Synthesis. 1,1'-((5,5',6,6'-tetramethyl-2,2'-dimethoxy-1,1'biphenyl-3,3'-(methylene))bis(1H-benzimidazole) L: A round bottom flask was charged with benzimidazole (0.339 g, 2.86 mmol, 2.1 eq.), K 2 CO 3 (0.563 g, 4.08 mmol, 3 eq.). 3,3'-bis(chloromethyl)-2,2-dimethoxy-5,5',6,6'tetramethyl-1,1'-biphenyl (0,5 g, 1.36 mmol, 1 eq.) was then solubilized in acetonitrile (15mL) freshly distilled on CaH 2 and was transferred to the flask. The solution was stirred at room temperature during 1h. The reaction mixture is then heated to reflux and is maintained under stirring 18 h. After cooling, the crude product was firstly filtered. The solid obtained, was extracted with CH 3 CN (3x15 mL). The pale yellow solution was then concentrated and purified by column chromatography (AcOEt/MeOH : 100/0; 90:10; 80/20) to afford a white solid (0.432 g, 0.81 mmol, 60 %) 1 H NMR (300 MHz, CD 3 CN, 300 K) (δ ppm) : 8.0 (s, 2H, H-Ar) ; 7.7-7.6 (m, 2H, H-Ar) ; 7.5-7.4 (m, 2H, H-Ar) ; 7.3-7.2 (m, 4H, H-Ar) ; 7.0 (s, 2H, H-Ar) ; 5.4 (d, 2 J = 4.2 Hz, 4H, CH 2 ) ; 3.2 (s, 6H, OCH 3 ) ; 2.2 (s, 6H, CH 3 ) ; 1.8 (s, 6H, CH 3 ).

13

C NMR (100 MHz, CD 3 CN) (δ ppm) : 153. 7 ; 143.6 ; 136.8 ; 133.7 ; 132.6 ; 131.3 ; 129.5 ; 126.1 ; 122.2 ; 121.4 ; 119.3 ; 110.4 ; 59.7 ; 43.3 ; 18.8 ; 15.6 146.3 ; 137.8 ; 132.8 ; 132.6 ; 130.9 ; 130.6 ; 124.1 ; 123.7 ; 111.9 ; 59.1 ; 45.9 ; 29.6 ; 18.7; 15.8 Suitable crystals were mounted and transferred into a cold nitrogen gas stream. Intensity data was collected with Bruker Kappa-APEX2 systems using fine-focus sealed tube Mo-Kα (1) or micro-source Cu-Kα (2) radiations. Unit-cell parameters determination, data collection strategy, integration and absorption correction were carried out with the Bruker APEX2 suite of programs. The structures were solved with SIR92 12 (1) or SHELXT-2014 13 (2) and refined anisotropically by full-matrix least-squares methods with SHELXL-2014 14 using the WinGX suite. [START_REF] Farrugia | Chiral two bladed ZnL 2 metallacage[END_REF] The structures were deposited at the Cambridge Crystallographic Data Centre with numbers CCDC 1534238-1534239 and can be obtained free of charge via www.ccdc.cam.ac.uk.

Crystal

Scheme 1 .

 1 Scheme 1. Synthesis of the ligand 1,1-((5,5',6,6'-tetramethyl-2,2'dimethoxy-3,3'(methylene))bis(1H-benzimidazole) L.

Figure 1 .

 1 Figure 1. View of the cationic part of the homochiral complex (R,R)-[Co(L) 2 ][BF 4 ] 2 (1) (C grey, O red, N blue, Co pink; H atoms are omitted for clarity). Selected bond lengths (Å) and angles (°) : Co(1)-N(1) = 2.003(2), Co(1)-N(4) = 1.983(2), N(1)-Co(1)-N(1) = 114.33, N(4)-Co(1)-N(4) = 106.35, N(1)-Co(1)-N(4) = 108.73.

  Figure 2. 1 H NMR spectra in CD 3 CN for a) ligand L and b) complex [Zn(L) 2 ][BF 4 ] 2 (2). In a similar way to 1, the formation of a racemic mixture of homochiral complexes (R,R)-[Zn(L) 2 ][BF 4 ] 2 (2) and (S,S)-[Zn(L) 2 ][BF 4 ] 2 (2) is observed.

Figure 3

 3 Figure 3 View of the cationic part the homochiral (R,R)-[Zn(L) 2 ][BF 4 ] 2 (2) (C grey, O red, N blue, Zn turquoise blue; H atoms are omitted for clarity). Selected bond lengths (Å) and angles (°) : Zn(1)-N(1) = 2.00 (2), Zn(1)-N(4) = 1.988(2), N(1)-Zn(1)-N(1) = 114.77(13), N(4)-Zn(1)-N(4) = 112.19(14), N(1)-Zn(1)-N(4) = 106.21(9), N(1)-Zn(1)-N(4) = 108.79(9).

[

  Scheme 3. Anion metathesis of rac-[Zn(L) 2 ][BF 4 ] 2 (2) and formation of the pair of diastereoisomers (R,R)-[Zn(L) 2 ][-TRISPHAT] 2 (3a) and (S,S)-[Zn(L) 2 ][-TRISPHAT] 2 (3b)

  1 H NMR spectrum of (R,R)-[Zn(L) 2 ][-TRISPHAT] 2 (3a) and (S,S)-[Zn(L) 2 ][-TRISPHAT] 2 (3b) recorded in CD 3 CN shows the presence of two sets of signals which is in agreement with the formation of two diastereoisomers (see Figure SI), in particular the presence of two signals for Ha for both isomers at 8.20 ppm and 8.30 ppm respectively. This base-to-base line separation observed in the 1 H NMR spectrum can be attributed to the ion-pairing between the dicationic complexes and the -TRISPHAT anion.

  Supporting information). At a [1+1] L/Zn mixture, broad signals are observed in the aromatic region; however upon addition of another equivalent of the ligand a rapid formation of sharp signals in the aromatic region becomes visible, suggesting the formation of the target homochiral metallacage (see Figure SII ). No formation of the other heterochiral diastereomer was detected. This data suggest indeed that homochiral metallamacrocycles are favoured by kinetic and thermodynamic factors which might originate from the geometry of the metal centre (tetrahedral) and also the nature of the atropoisomeric chiral ligands.

  ); M = Zn, (2a) and (S,S)-[M(L) 2 ][BF 4 ] 2 M = Co, (1b); M = Zn, (2b) but obtained in racemic mixture. These compounds can be converted to the corresponding diastereomeric mixture by anion metathesis using the chiral -TRISPHAT anion as shown by 1

  according to published methods. All experimental manipulations were carried out under argon using Schlenk techniques. IR spectra were recorded on a Bruker Tensor 27 equipped with a Harrick ATR. Elemental analyses were performed by the microanalytical laboratory of ICSN, Gif-sur Yvette. NMR experiments were carried out on a Bruker Avance 300 MHz spectrometer operating at 300 K with chemical shifts references to residual solvent peaks. Chemical shifts are reported in parts per million (ppm) and coupling constant (J) in hertz (Hz). Standard abbreviations indicating multiplicity were used as follows: m = multiplet, t = triplet, d = doublet, s = singlet, b = broad.

31P

  NMR (121 MHz, CD 3 CN) (δ ppm) :-81.1 (s, -TRISPHAT); IR (ATR): (ν, cm -1 ) 2936 (ν CH 3 ) ; 1446 (ν C=C Ar) ; 1389 ; 1236 (ν C-N Ar) ; 1080 ; 1034 ; 989 (ν P-O) , 742 ; 718 ; 669(ν C-Cl) ; 620 ; 552 ; 424 ; CD (0.05 mM, CH 3 CN) (nm) : (+) 211, (-

  10317 independent (R int = 0.0385), 7515 observed [I > 2σ(I)], 445 parameters, final R indices R1 [I > 2σ(I)] = 0.0515 and wR2 (all data) = 0.1479, GOF(on colourless prism, C 68 H 68 N 8 O 4 Zn, 2(BF 4 ), 2(C 2 H 3 N), monoclinic C2/c, a = 35.9399(12) Å, b = 9.2811(3) Å, c = 21.8244(7) Å, α = 90° , β = 112.179(3)°, γ = 90°, V = 6741.1(4) Å 3 , Z = 4, T = 200(1) K, μ = 1.176 mm -1 , 24622 reflections measured, 5906 independent (R int = 0.0705), 4037 observed [I > 2σ(I)], 445 parameters, final R indices R1 [I > 2σ(I)] = 0.0480 and wR2 (all data) = 0.1246, GOF(on F 2 ) = 1.016, max/min residual electron density 0.64/-0.29 eÅ -3 .

Acknowledgements

Université Pierre et Marie Curie-Paris 6, Centre National de la Recherche Scientifique are gratefully acknowledged.

CCDC 1534238 and 1534239. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.


Pierre Henri Lanoë
email: pierre-henri.lanoe@upmc.fr

Btissam Najjari
email: najjari015@gmail.com

Florine Hallez
email: florine.hallez@etu.upmc.fr

Geoffrey Gontard
email: geoffrey.gontard@upmc.fr

Hani Amouri
email: hani.amouri@upmc.fr.

N-Heterocyclic Carbene Coinage Metal Complexes Containing Naphthalimide Chromophore: Design, Structure and Photophysical Properties

Keywords: N-heterocyclic Carbenes, Coinage Metals, Photophysical Properties

A series of novel N-heterocyclic carbene coinage metal complexes containing a naphthalimide (NI) chromophore have been prepared and fully characterized. Two types of molecules are described those where the NI unit is directly attached to the carbene unit with the general formulae [(L 1 )-M-X], M = Cu, X = Cl (1a); M = Ag, X = I (1b) and M = Au, X= Cl, (1c). While in the second family a -extended carbene ligand precursor L 2 H + I -(3) was prepared where the NI unit is distant from the imidazole unit via a phenyl-alkyne bridge. Only two N-heterocyclic carbene metal complexes were prepared [(L 2 )-M-Cl], M = Cu (2a) and M = Au (2c). The related silver carbene compound could not be isolated. The molecular structure of the carbene complex 1c was determined and confirmed the formation of the target compound. Interestingly the structure shows the presence of an aurophilic interaction Au----Au at 3.407Å between two individual molecules.

The photophysical properties of the compounds were investigated in solution at room temperature. Preliminary results suggested that all compounds are luminescent and act as blue emitters (420-451 nm). These transition emissions can be attributed to intraligand origin of the NI chromphore. Moreover the carbene complexes featuring L 2 ligand with -extended system were found to be more luminescent.

Introduction

N-heterocyclic carbene (NHC) ligands have received much attention since the isolation of the free imidazole-2-ylidene ligand by [START_REF] Arduengo | A Stable Crystalline Carbene[END_REF] [START_REF] Arduengo | A Stable Crystalline Carbene[END_REF]. However the first metal complexes were reported back in 1965 by Ofele and Wanzlick et al [START_REF] Ofele | A New Transition-Metal Carbon Complexe 1,3-Dimethyl-4-Imidazolinylid-2-Ene Pentacarbonylchromium[END_REF][START_REF] Wanzlick | Direct Synthesis of a Mercury Salt-Carbene Complex[END_REF]. Indeed they allow the formation of stable compounds that have important applications in various fields of chemistry [START_REF] Huynh | The Organometallic Chemistry of N-Heterocyclic Carbenes[END_REF][START_REF] Mercs | Beyond catalysis: N-heterocyclic carbene complexes as components for medicinal, luminescent, and functional materials applications[END_REF] such as organometallics [START_REF] De Fremont | Synthesis, properties, and organometallic chemistry[END_REF], homogeneous catalysis [START_REF] Herrmann | N-heterocyclic carbenes: A new concept in organometallic catalysis[END_REF], metallosupramolecular chemistry, metallodrugs [START_REF] Hindi | The Medicinal Applications of Imidazolium Carbene-Metal Complexes[END_REF] and more recently as luminescent materials [START_REF] Visbal | N-Heterocyclic carbene metal complexes: photoluminescence and applications[END_REF][START_REF] Moussa | Synthesis and Luminescence Properties of Cycloplatinated Complexes with a Chelating N ^ C Pyridine-Derived N-Heterocyclic Carbene -Influence of 2,4,6-Triphenylphosphinine versus Triphenylphosphine[END_REF][START_REF] Moussa | C^ N-coordinated Pd(II) and Pt(II) complexes of a tridentate N-heterocyclic carbene ligand featuring a 6-membered central ring: synthesis, structures and luminescence[END_REF]. In the latter a wide range of luminescent complexes were prepared displaying various properties however efforts were focused on N-heterocyclic coinage metal complexes because they tend to form metal--metal interactions at the supramolecular level which might add a novel property to their luminescent properties and also for their potential application as light emitting devices [START_REF] Chow | Photophysical Properties, and Molecular Aggregation of Gold(I) Complexes Containing Carbon-Donor Ligands[END_REF][START_REF] Lin | Coinage Metal-N-Heterocyclic Carbene Complexes[END_REF][START_REF] Lin | Review of gold(I) N-heterocyclic carbenes[END_REF][START_REF] Kriechbaum | Characterization and Luminescence of Gold Complexes Bearing an NHC Ligand Based on the Imidazo[1,5-a]quinolinol Scaffold[END_REF][START_REF] Hong | From Spherical to Leaf-Like Morphologies: Tunable Supramolecular Assembly of Alkynylgold(I) Complexes through Variations of the Alkyl Chain Length[END_REF].

We recently reported the synthesis and characterization of a family of cyclometalated iridium carbene complexes containing a naphthalimide chromophore [START_REF] Lanoe | Deep-Red Phosphorescent Iridium(III) Complexes with Chromophoric N-Heterocyclic Carbene Ligands: Design, Photophysical Properties, and DFT Calculations[END_REF]. The latter behaved as deep red phosphorescent compounds with good quantum yields and long lifetimes. Thus we sought to extend our approach to other metal chromophores mainly coinage metals. In fact due to their linear geometry we expected to promote metal--metal interactions [START_REF] Chow | Photophysical Properties, and Molecular Aggregation of Gold(I) Complexes Containing Carbon-Donor Ligands[END_REF][START_REF] Nitsch | Cuprophilic interactions in highly luminescent dicopper(I)-NHC-picolyl complexes -fast phosphorescence or TADF?[END_REF][START_REF] Penney | Aurophilicity in Action: Fine-Tuning the Gold(I)-Gold(I) Distance in the Excited State To Modulate the Emission in a Series of Dinuclear Homoleptic Gold(I)-NHC Complexes[END_REF] and hence add a novel property to this kind of compounds relative to the cyclometalated iridium compounds. In this paper we describe the synthesis and photophysical properties of a novel class of N-heterocyclic carbene complexes of Cu(I), Ag(I) and Au(I) containing a naphthalimide chromophore. Two types of compounds are described (i) those where the naphthalimide is directly linked to the carbene unit, while in the other case (ii) the organic chromophore is distant from the carbene unit via an alkyne arene linkage (Figure 1).

Figure 1.

Ligand precursors L 1 -H + I -and L 2 -H + I -and the related NHC carbene complexes with naphthalimide chromophore described in this work.

Results and Discussions

Synthesis and characterization of the imidazolium salts

The carbene ligand precursor L 1 -H + I -was prepared according to our previously reported procedure [START_REF] Lanoe | Deep-Red Phosphorescent Iridium(III) Complexes with Chromophoric N-Heterocyclic Carbene Ligands: Design, Photophysical Properties, and DFT Calculations[END_REF]. For L 2 -H + I -containing an extended carbon skeleton, the product was prepared in several steps. Thus reaction of imidazole with p-bromofluorobenzene in presence of potassium phosphate provided 1-(4-bromophenyl)-imidazole (6) (scheme 1) [START_REF] Diness | Catalyst-Free N-Arylation Using Unactivated Fluorobenzenes[END_REF]. Subsequent Sonogashira-Hagihara cross coupling reaction in toluene gave the desired compound 5 in good yield (90%). Cleavage of the Si-C bond using TBAF provided the free alkyne, which was directly engaged in the next step without purification. A second Sonogashira-Hagihara cross coupling reaction between the latter compound and naphthalimide-Br (NI-Br) led to compound 4 in good yield (78%).

The methylation reaction took place in refluxing CH3CN with excess of MeI to form the azolium salt L 2 -H + I -in satisfactory yield (63%). Full characterizations of these compounds are given in the experimental section. Scheme 1. Synthesis of the carbene ligand precursor L 2 -H + I -(3).

Synthesis and characterization of the NHC coinage metal complexes.

The novel coinage metal carbene complexes were obtained following the silver carbene transfer route as described previously in the literature [START_REF] Wang | Facile synthesis of silver(I)-carbene complexes. Useful carbene transfer agents[END_REF][START_REF] Visbal | Simple and efficient synthesis of [MCI(NHC)] (M = Au, Ag) complexes[END_REF]. Thus treatment of Ag2O with L 1 -H + I -in dry CH2Cl2 solution and subsequent transmetallation with the appropriate metal sources (i.e. CuCl or (tht)AuCl leads to the formation of Cu(I) and Au(I) complexes in moderate to good yields [(L 1 )-Cu-Cl] (1a) (30%) [(L 1 )-Au-Cl] (1c) (72%). For comparison purposes the silver complex was also prepared [(L 1 )-Ag-I] (1b) in 94% yield.

On the other hand we found that using L 2 -H + I -carbene precursor the reactions were more tedious and required the use of a mixture of CH3NO2/CH2Cl2 for solubility purposes. For instance the [(L 2 )-Cu-Cl] (2a) and ([(L 2 )-Au-Cl] (2c) were obtained (33%) and (72%) yield respectively after 16 hours of reaction using Ag2O precursor. Despite all our efforts we were unable to isolate the silver carbene complex [(L 2 )-Ag-I] (2b). All compounds have been characterized by 1 H and 13 C NMR spectroscopy, elemental analysis, moreover the X-ray molecular structure of 1c was determined and confirmed the formation of the desired compound (vide infra). In particular the 13 C{ 1 H} NMR spectra of the azolium salts showed the presence of a singlet for the C-H group around  135 ppm while the related metal carbene complexes 1b, 1c and 2c displayed a singlet for the carbene carbon centers in the range of  171-182 ppm. Scheme 2. Synthesis of the novel carbene coinage metal complexes.

X-ray molecular structure of the N-heterocyclic gold carbene complex [(L 1 )-Au-Cl] (1c)

Convenient crystals for X-ray diffraction crystallography were grown by slow vapor diffusion of diethylether into a dichloromethane solution of [(L 1 )-Au-Cl] (1c) (Table S1). A view of the structure is given in Figure 2 with selected bond distances and angles. The structure confirms the formation of the target gold complex 1c. Moreover it shows the geometry around the Au(I) center is almost linear with a Ccarbene-Au-Cl angle of approximately 175.88(7)°. The Ccarbene-Au and Au-Cl distances are 1.985(5) Å and 2.287(0), respectively typical to those reported for previous complexes containing a simple carbene ligand [START_REF] Kriechbaum | Characterization and Luminescence of Gold Complexes Bearing an NHC Ligand Based on the Imidazo[1,5-a]quinolinol Scaffold[END_REF][START_REF] Gimeno | N-Heterocyclic Carbene Coinage Metal Complexes as Intense Blue-Green Emitters[END_REF][START_REF] Wang | Gold(I) N-heterocyclic carbene and carbazolate complexes[END_REF]. In addition, the planes of the imidazole-2-ylidene moiety and the NI moiety show an angle of approximately of 65.81(8)°. To our knowledge this is the first molecular structure of a gold carbene complex tethered to a naphthalimide chromophore. An examination of the crystal packing reveals that the individual molecules display Au---Au and - interactions (Figure 3). Indeed molecules interact pairwise in head-to-tail fashion through aurophilic interactions with Au … Au distance of 3.407(1) Å. Furthermore, the molecules demonstrate additional - interactions around 3.40 Å to form a 2D supramolecular structure. We then examined their photophysical properties.

Photophysical properties.

All compounds have been studied in diluted air equilibrated CH2Cl2 solution except for silver carbene complex [(L 1 )-Ag-I] (1b) which was not stable in CH2Cl2 solution and hence could not be investigated. The imidazolium salts L 1 -H + I -and L 2 -H + I -display different absorption spectra for instance the L 2 series are bathochromically shifted relative to L 1 series due to -conjugation (Figure 3). More over they show additional absorption peaks at 280-320 nm, which are not present in the L 1 -type ligand and related complexes. These bands are assigned to * involving the acetylide unit (Figure 3). Furthermore the L 1 -H + I and the related carbene complexes -[(L 1 )-Cu-Cl] (1a) and [(L 1 )-Au-Cl] (1c), show a broad absorption band between 300 nm and 400 nm (12.0 x 10 3 L.mol -1 .cm -1 <15.3 x 10 3 L.mol -1 .cm -1 ), which might be a superposition of at least two bands, (Figure 4 and table 1). These bands might be attributed to 1 n* or * transitions which are in agreement to those reported for the functionalized naphthalimide chromphore [START_REF] Alexiou | The Uv-Visible Absorption and Fluorescence of Some Substituted 1,8-Naphthalimides and Naphthalic Anhydrides[END_REF]. Remarkably the azolium salt L 1 -H + I displayed a long tail up to 450 nm reminiscent of an aggregation phenomenon that is occurring in CH2Cl2. Indeed we then recorded the UV visible spectrum of L 1 -H + I at the same concentration but in CH3CN instead (Figure S1) which showed the disappearance of this low energy band. Such aggregation phenomena have been reported previously to other functionalized naphthalimide system [START_REF] Srivastava | Tuning of Aggregation Enhanced Emission and Solid State Emission from 1,8-Naphthalimide Derivatives: Nanoaggregates, Spectra, and DFT Calculations[END_REF].

As for the azolium salt L 2 -H + I (3) and the related carbene complexes [(L 2 )-Cu-Cl] (2a) and [(L 2 )-Au-Cl] (2c), this broad absorption band appears between 320nm and 430nm and is red shifted compared to the previous compounds we also note that the molar absorptivity is higher. Both features can be explained by the extended -conjugation as a result of the to the presence of the phenyl-ethynyl bridge between the carbene unit and the naphthalimide (NI) chromophore.

Preliminary results showed that the metal complexes 1a-2a and 1c-2c are luminescent at room temperature in CH2Cl2 solution and displayed blue emissions in the range of 420 to 451 nm (Table 1).

For instance the metal complexes containing L 1 -type ligand showed a slight red shift emission relative to free to the azolium salt L 1 -H + I -(Figure 4). Similarly the carbene metal complexes with L 2 -type ligand showed also a slight red shift relative to the free ligand L 2 -H + I. These emissions are clearly intraligand interactions centered at the naphthalimide moiety. Similar results were reported for coinage carbene complexes displaying organic chromophores [START_REF] Chow | Photophysical Properties, and Molecular Aggregation of Gold(I) Complexes Containing Carbon-Donor Ligands[END_REF][START_REF] Kriechbaum | Characterization and Luminescence of Gold Complexes Bearing an NHC Ligand Based on the Imidazo[1,5-a]quinolinol Scaffold[END_REF][START_REF] Gimeno | N-Heterocyclic Carbene Coinage Metal Complexes as Intense Blue-Green Emitters[END_REF]. On the other hand we found that the complexes with L 2 -type ligand displayed higher quantum yields (Table 1). Further studies at low temperature and in solid state will be conducted on these compounds in order to better understand their optical behavior.

Compound abs/nm (L.mol -1 .cm -1 x 10 3 ) em/nm (fluo a ) L 1 have been estimated by taking 9,10-diphenylanthracene in cyclohexane as a reference with QY = 0,90 [START_REF] Brouwer | Standards for photoluminescence quantum yield measurements in solution (IUPAC Technical Report)[END_REF]. b)max c) exc = 340 nm. d) exc = 350 nm.

Concluding remarks

In this work we reported the synthesis of first family of coinage metal complexes containing a choromophoric N-heterocyclic carbene ligands. For comparison purposes, two types of compounds were prepared those where the carbene unit is directly linked to the naphthalimide chromophore [(L 1 )-M-Cl], M = Cu (1a), M = Ag, (1b) and M = Au (1c) while in the second series the chromophore is moved away via an alkyne-arene linkage [(L 2 )-M-Cl], M = Cu (2a), M = Au, (2c). The X-ray molecular structure of the gold carbene complex 1c was determined and showed the presence of aurophilic interaction. Preliminary results suggest that these compounds are luminescent at room temperature and act as blue emitters. Moreover the complexes with extended -skeleton were found to be more luminescent. Our efforts are currently devoted to extend this methodology to related coinage complexes containing carbon-donor ligands instead of the halogen groups to improve their quantum yields and seek applications as organic light emitting diodes.

Experimental section

General experimental methods

Commercially available reagents were purchased from Sigma-Aldrich, Alfa Aesar, Acros Organics, TCI Chemical, Strem or Fluorochem and used as received unless otherwise specified. Solvents were obtained from same commercial sources and used without further purification unless otherwise specified. Et3N, CH2Cl2 and Et2O were distilled respectively on sodium, CaH2 and sodium/benzophenon. Toluene was stored over 4 Å molecular sieve under Ar. Copper(I) chloride has been prepared according to a reported procedure [START_REF] Armarego | Purification of Laboratory Chemicals Fifth Edition[END_REF] and stored in a Schlenk tube under Ar. Glassware was oven-dried prior to use. 39,52 ppm). Absorption measurement has been performed on a Jasco V-670 and luminescence measurement on a Jasco FP-8300 Fluorometer.

Synthesis of compound 5

In an oven-dried Schlenk tube under Ar atmosphere, 1-(4-Bromophenyl)-imidazole 6 (2 g, 8.97 mmol), CuI (51 mg, 0,27 mmol) and Pd(PPh3)2Cl2 (189 mg, 0.27 mmol) were introduced in a mixture of toluene (15 mL) and Et3N (2 mL). The solution was degassed three times using freeze-pump-thaw technique. TMSA (1 mL, 6.72 mmol) was added to the solution and heated at 80 °C overnight (16h). The mixture was then heated at 50°C and solvents were evaporated to dryness. At r.t., the dark crude material was treated with Et2O and the suspension was filtrated on Dicalite®. The solvent was evaporated and a column chromatography (SiO2, ethylacetate/cyclohexane from 7/3 to 1/0) to give a greyish compound 5 (1.953 g, 90%).

Synthesis of compound 4

Tetrabutylamonium fluoride monohydrate (1.153 g, 4.41 mmol) was added to a solution of compound 5 (1 g, 4.16 mmol) in THF (25 mL). The reaction was monitored by TLC (SiO2, ethylacetate) and after full conversion, deionized water (20 mL) was added and the aqueous phase was extracted three times with Et2O. The combined organic layers were washed two times with brine, dried over MgSO4 and solvents were removed under reduce pressure. The crude product was engaged in the next step without further purification. In a dry Schlenk tube under Ar, the crude alkyne (603 mg, 3.59 mmol), 4-bromonaphtalimide (1.312 g, 3.95 mmol), Pd(PPh3)2Cl2 (126 mg, 0.18 mmol) and CuI (34 mg, 0.18 mmol) were dissolved/suspended in a mixture of toluene (20 mL) and Et3N (2 mL). The solution was degassed three times. The mixture was then heated at 80 °C and the reaction was monitored by TLC (SiO2, ethylacetate/C6H12). After full conversion (roughly 2hrs), the solvents were removed and the dark material was treated with CH2Cl2. The dark solution was filtrated on Dicalite® and the solvents were removed under reduce pressure. A chromatography column was performed (SiO2, from pure CH2Cl2 to CH2Cl2/MeOH 7/3). The fractions containing the compound were combined and the solvent was removed under vacuum. The yellow solid was dissolved in CH2Cl2, washed 3 times with a solution of K2CO3 (1 N) and dried over MgSO4. After evaporation of the solvent, the compound was obtained as yellow solid (1,175 g, 78%).

To a hot solution of 4 (156 mg, 0.37 mmol) in distilled CH3CN (20 mL) was added MeI (170 µL, 2.6 mmol) and the solution was refluxed overnight. The solvent was evaporated to dryness and the crude material was stirred 30 min with Et2O (40 mL). The solution was then filtered on a frit and the brown solid was wash three times with a small amount of Et2O to give a brown solid (133 mg, 63 %).

Synthesis of Complex 1b

An oven-dried Schlenk under Ar was loaded with L 1 -H + I -(143 mg, 0.3 mmol) and Ag2O (38 mg, 0.17 mmol) and the solids were suspended in a mixture of distilled CH2Cl2 and CH3CN (1/1, 20 mL). The solution was stirred during 4-5h and protected from light using aluminum foil. Then a pinch of active carbon was added and the solution was filtered on Dicalite® and washed with a small amount of CH2Cl2. The solution was reduced under vacuum, subsequent addition of Et2O provided a precipitate. The supernatant was filtered off with a cannula and the solid was dried under vacuum. 1b was obtained as a green solid (96 mg, 94%). General procedure for the synthesis of 1a and 1c

An oven-dried Schlenk under Ar was loaded with the imidazolium salt (1 eq.) and Ag2O (from 0.5 eq. to 0.56 eq.) and the solids were suspended in a mixture of CH2Cl2 and CH3CN (1/1). The solution was stirred 4-5h under light protection using aluminum foil. Then a pinch of active carbon was added and the solution was filtered with a cannula fitted with a filter paper and the black solid washed with a small amount of CH2Cl2. The solution was reduced under vacuum subsequent addition of Et2O provided a precipitate. The supernatant was filtrate off with a cannula fitted with a filter paper and the solid was dried under vacuum. The desired metal salt was then added to the crude Ag(I) complex in CH2Cl2. The solution was stirred overnight at r.t. The yellowish precipitate was filtered off with a cannula fitted with a filter paper. The solid was washed two times with CH2Cl2 and the solution was concentrated under vacuum, subsequent addition of Et2O provided the desired complex which was separated and dried.

For complex 1a L General procedure for the synthesis of 2a and 2c

In an oven-dried Schlenk tube protected from light with aluminum foil, iodide salt and Ag2O were suspended in CH2Cl2/CH3NO2 mixture (4/1, v/v). After 5-6h, a yellow suspension was formed and the desired metal precursor (whether (tht)AuCl or CuCl) was added to the suspension. After 12-16h of stirring, the solution was filtered off with a cannula and the filtrate was separated into a Schlenk tube as translucent yellow solution. The remaining solid was washed three times with CH2Cl2 and the filtrate was concentrated under vacuum subsequent Et2O addition provided a precipitate, the mixture was then allowed to stand in a freezer for several hours. The supernatant was filtered off with a cannula fitted with a filter paper and the yellow solid was dried under vacuum.

For Complex 2a

Figure 2 .

 2 Figure 2. View of the molecular structure of the gold carbene complex [(L 1 )-Au-Cl] (1c). Selected bond distances (Å) and angle (°). Au(1)C(1) = 1.986(2), Au(1)Cl(1) = 2.287(1), N(1)C(1) = 1.353(3), N(1)C(3) = 1.388(3), N(1)C(5) = 1.427(3), N(2)C(1) = 1.338(3), N(2)C(2) = 1.381(3), N(2)C(4) = 1.457(3), C(1)Au(1) Cl(1) = 175.88(7), N(1)C(1) N(2) = 105.4(2).

Figure 3 .

 3 Figure 3. Crystal packing of 1c showing aurophilic Au---Au contact at 3.407(1) Å between two individual molecules in head to tail fashion and - interactions at 3.40 Å between two naphthalimide units to generate a 2D supramolecular structure.

Figure 4 .

 4 Figure 4. Absorption spectra for the azolium salts of L 1 -H + I -, L 2 -H + I -and the carbene metal complexes 1a-2a and 1c-2c in CH2Cl2 solution at room temperature.

Figure 5 .

 5 Figure 5. Normalized emission for the azolium salts of L 1 -H + I -, L 2 -H + I -and the carbene metal complexes 1a-2a and 1c-2c in CH2Cl2 solution at room temperature.

1 H

 1 NMR spectra were recorded on a 300 MHz and on a 400 MHz in CDCl3, CD2Cl2 or (CD3)2SO and data are reported as follows: chemical shift in ppm from tetramethylsilane with the solvent as an internal indicator (CDCl3 7.26 ppm, CD2Cl2 5,32 ppm and (CD3)2SO 2,50 ppm), multiplicity (s = singlet, d = doublet, t = triplet, q = quartet, quint = quintet, m = multiplet or overlap of non-equivalent resonances), integration. 13 C NMR spectra were recorded either on a 75.4 MHz or on a 101 MHz in CDCl3, CD2Cl2 or (CD3)2SO and data are reported as follows: chemical shift in ppm from tetramethylsilane with the solvent as an internal indicator (CDCl3 77.16 ppm, CD2Cl2 53,84 ppm and (CD3)2SO

1 H

 1 NMR (300 MHz, CDCl3) δ 8.70 (dd, J = 8.4 Hz, J = 1.1 Hz, 1H), 8.64 (dd, J = 7.3 Hz, J = 1.2 Hz, 1H), 8.56 (d, J = 7.6 Hz, 1H), 7.96 (d, J = 7.6 Hz, 1H), 7.94 (s, 1H), 7.84 (dd, J = 8.4 Hz, J = 7.3 Hz, 1H), 7.78 (d, J = 8.5 Hz, 2H), 7.48 (d, J = 8.6 Hz, 2H), 7.35 (d, J = 1.4 Hz, 1H), 4.35 -4.03 (m, 2H), 1.86 -1.64 (m, 2H), 1.45 (h, J = 7.3 Hz, 2H), 0.99 (d, J = 7.3 Hz, 3H).

Table 1 .

 1 Absorption and emission data for the azolium salts of L 1 and L 2 , and the carbene metal complexes 1a-2a and 1c-2c from CH2Cl2 solutions at room temperature. a) Quantum yields (QYs)

	-H + I -	330 (14.0) 345 (13.3)	410 b , 430 (0.21) c
	[(L 1 )-Cu-Cl] (1a)	332 (13.8); 346 (14.2)	426 (0.07) c
	[(L 1 )-Au-Cl] (1c)	335 (13.7); 349 (12.9)	451 (0.01) c
	L 2 -H + I -(3)	285 (15.8); 296 (18.0); 372 (34.3); 389 (30.2)	406, 424 b (0.73) d
	[(L 2 )-Cu-Cl] (2a)	284 (14.2); 299 (13.2); 376 (13.2); 3393 (24.2)	428 (0.20) d
	[(L 1 )-Au-Cl] (2c)	284 (12.4); 298 (12.1); 375 (25.6); 393 (21.9)	429 (0.29) d

  1 H NMR (300 MHz, DMSO) δ 9.90 (s, 1H), 8.86 (d, J = 8.3 Hz, 1H), 8.61 (d, J = 7.2 Hz, 1H), 8.53 (d, J = 7.6 Hz, 1H), 8.42 (s, 1H), 8.21 -8.09 (m, 3H), 8.09 -7.89 (m, 4H), 4.08 (t, J = 7.4 Hz, 2H), 4.00 (s, 3H), 1.66 (p, J = 15.3 Hz, J = 7.7 Hz, 2H), 1.39 (h, J = 7.5 Hz, 2H), 0.96 (t, J = 7.3 Hz, 3H). 13 C{ 1 H} NMR (75 MHz, DMSO) δ 163.1, 162.8, 136.2, 135.1, 133.7, 131.9, 131.3, 130.8, 129.9, 128.4, 127.3, 125.5, 124.6, 122.7, 122.4, 122.0, 120.7, 96.9, 87.8, 36.2, 29.6, 19.8, 13.7. Analysis Calcd. for C28H24IN3O2.1/10Et2O, C, 59.97; H, 4.43; N, 7.39; found C, 59.85; H, 4.18; N, 7.34.

  J = 7.4 Hz, J = 7.3 Hz, 2H), 0.99 (t, J = 7.4 Hz, 3H).13 C{1 H} NMR (101 MHz, CD2Cl2) δ 164.0, 163.4, 132.3, 131.0, 129.5, 128.8, 128.7, 128.1, 126.1, 124.5, 123.9, 40.7, 30.5, 20.8, 14.0. -H + I -(95 mg, 0.2 mmol), Ag2O (23 mg, 0.1 mmol) and CH2Cl2/CH3CN (14 mL). (tht)AuCl (64 mg, 0.2 mmol) and CH2Cl2 (10 mL). The complex was obtained as an off white solid (73 mg, 72%).1 H NMR (400 MHz, CD2Cl2) δ 8.68 (d, J = 7.7 Hz, 1H), 8.67 (dd, J = 7.0 Hz, J = 1.4 Hz, 1H), 7.94 -7.79 (m, 3H), 7.31 (s, 2H), 4.18 (t, J = 7.6 Hz, 2H), 4.02 (s, 3H), 1.79 -1.67 (m, 2H), 1.45 (h, J = 7,5 Hz, 2H), 0.98 (t, J = 7.4 Hz, 3H).13 C{ 1 H} NMR (101 MHz, CD2Cl2) δ 173.9, 163.9, 163.4, 140.4, 132.3, 130.8, 129.3, 128.8, 128.6, 128.4, 126.8, 124.8, 123.8, 123.7, 123.0, 40.7, 39.0, 30.5, 20.7, 14.0. Analysis calcd for C20H19AuClN3O2 .1/4CH2Cl2: C, 41.43 ; H, 3.35 ; N, 7.43 ; found, C, 41.00; H, 3.17; N, 7.19.

	1 -H + I -(95 mg, 0.2 mmol), Ag2O (26 mg, 0.11 mmol) and CH2Cl2/CH3CN (14 mL). CuCl (20 mg, 0.2 mmol) and
	CH2Cl2 (10 mL). The complex was obtained as an yellow solid (22 mg, 30%). Analysis calcd for C20H19CuClN3O2
	.1/4CH2Cl2: C, 53.62; H, 4.33; N, 9.26; found, C, 53.70; H, 4.57; N, 8.99. 1 H NMR (400 MHz, CD2Cl2) δ 8.77 -8.64
	(m, 2H), 8.00 (dd, J = 8.5 Hz, J = 1.2 Hz, 1H), 7.92 -7.80 (m, 2H), 7.33 (s, 1H), 7.27 (s, 1H), 4.22 -4.12 (m, 2H), 4.03
	(s, 3H), 1.81 -1.61 (m, 2H), 1.45 (h, For complex 1c
	L 1

(http://creativecommons.org/licenses/by/4.0/).

Acknowledgments: We thank CNRS, Centre National de la Recherche Scientifique and Sorbonne Universités, UPMC, Univ. Paris 06 for supporting this work.

L 2 -H + I -(84 mg, 0.15 mmol), Ag2O (19 mg, 0.08 mmol), CuCl (15 mg, 0.15 mmol) , CH2Cl2 (25 mL) and MeNO2 (5 mL). The complex was obtained as a yellow solid (53 mg, 63%). 1 H NMR (400 MHz, CD2Cl2) δ 8.77 (dd, J = 8.4 Hz, J = 1.2 Hz, 1H), 8.63 (dd, J = 7.3 Hz, J = 1.2 Hz, 1H), 8.55 (d, J = 7.6 Hz, 1H), 8.01 (d, J = 7.6 Hz, 1H), 7.94 -7.83 (m, 3H), 7.77 (d, J = 8.4 Hz, 2H), 7.33 (d, J = 1.6 Hz, 1H), 7.20 -7.06 (m, 1H), 4.22 -4.12 (m, 2H), 3.98 (s, 3H), 1.71 (p, J = 7.5 Hz, 2H), 1.45 (q, J = 7.5 Hz, 2H), 0.99 (t, J = 7.4 Hz, 3H). 13 For Complex 2c L 2 -H + I -(102 mg, 0.18 mmol), Ag2O (23 mg, 0.10 mmol), (tht)AuCl (58 mg, 0,18 mmol), CH2Cl2 (25 mL) and MeNO2 (5 mL). The complex was obtained as a yellow solid (38 mg, 33%). 1 3H), 1.71 (p, J = 7.5 Hz, 2H), 1.45 (q, J = 7.5 Hz, 2H), 0.99 (t, J = 7.4 Hz, 3H). 13 A single crystal of [(L 1 )-Au-Cl] (1c) was selected, mounted and transferred into a cold nitrogen gas stream.

Intensity data was collected with a Bruker Kappa-APEX2 system using fine-focus sealed-tube radiation.

Unit-cell parameters determination, data collection strategy, integration and absorption correction were carried out with the Bruker APEX2 suite of programs. The structure was solved with SHELXT-2014 C1 and refined anisotropically by full-matrix least-squares methods with SHELXL-2014 [START_REF] Sheldrick | A short history of SHELX[END_REF] using the WinGX suite [START_REF] Farrugia | WinGX suite for small-molecule single-crystal crystallography[END_REF].

Relevant data was deposited at the Cambridge Crystallographic Data Centre with number CCDC 1558193 and can be obtained free of charge via www.ccdc.cam.ac.uk.

Crystal data for (1c). Supplementary Materials: The following are available online at www.mdpi.com/link, Table S1: crystallographic data for complex [(L 1 )-Au-Cl] (1c), Figure S1: Absorption spectrum of the azolium salt L 1 -H + I -in CH3CN versus CH2Cl2 solution at same concentration and at room temperature.

Conflicts of Interest: The authors declare no conflict of interest.


A Servais
email: aude.servais@aphp.fr

S Gueguen

D Georges

B T Aurélia

L Sandrine

N Robert

T Lamia

R Marine

Serge Amselem

N Patrick

A Ntumba Mulunda

V Plennevaux

A Nolf

T Baudoux

N Broeders

I Simon

P Madhoun

J M Hougardy

A Le Moine

J Nortier

RaDiCo-ECYSCO, une cohorte européenne dédiée à la cystinose

Introduction

  Depuis 2017, un programme d'éducation thérapeutique du patient (ETP) inspiré de E'DIRE (Nephrolor) est proposé aux patients insuffisants rénaux chroniques (IRC) de notre service dans le but de leur transférer des savoirs et compétences qui faciliteront la gestion de leur maladie au quotidien. Le but de notre travail a été d'évaluer l'acquisition des connaissances durant leur parcours accompagné. Description Des entretiens individuels ont été menés et des questionnaires soumis aux patients répartis dans 3 cohortes annuelles, dont la dernière est en cours. Les connaissances étudiées ont été regroupées en 6 thèmes : -symptômes, causes et signes d'aggravation ; -paramètres biologiques et évolution ; -surveillance et auto mesure tensionnelle ; -activité physique adaptée ; -aspects diététiques ; -médicaments et toxiques, évalués au début du programme puis à 3 mois (thèmes 1 à 3) et à 6 mois (thèmes 4 à 6). Méthodes Nous avons utilisé une adaptation de la rosace des compétences de l'Association vosgienne des réseaux de santé afin de scorer et visualiser l'évolution des acquis. Les données ont été analysées en utilisant le test de Wilcoxon. Résultats Au total 38 patients (25 hommes et 13 femmes) âgés de 72 ± 11 ans ont été suivis (stades de l'IRC 3a [N = 5], 3b [N = 19] et 4 [N = 14]). Tous avaient des lacunes à divers degrés lors du diagnostic éducatif initial. Nous avons noté une évolution significative des connaissances durant le parcours éducatif comme l'illustre la Fig. 1 (p < 0,0001 pour chaque thème analysé). Conclusion Cette étude confirme que l'ETP spécifique à l'IRC représente une approche efficace et bénéfique pour la transmission des savoirs et des compétences utiles à la compréhension de la maladie et à son autogestion au quotidien. Il serait judicieux d'évaluer les résultats de l'appropriation de ces connaissances par les patients et de leur persistance dans le temps.

Fig. 1

 1 Fig. 1 Bénéfices de l'ETP dans l'IRC.