Electrosynthèse de nanoparticules métalliques en milieu liquide ionique supramoléculaire

La première partie de cette thèse décrit comment l'introduction de groupements alkoxyphényles en position 1 et 3 d'une unité imidazolium induit des propriétés supramoléculaires à ce matériau liquide ionique. L'étude s'intéresse à l'évolution des propriétés mésomorphes en fonction des modifications structurales apportées (longueur de la chaîne aliphatique) en s'appuyant sur une caractérisation complète des phases cristal liquides (microscopie optique à lumière polarisée, calorimétrie différentielle, diffraction de rayons X). Nous nous sommes également intéressés à l'activité catalytique du complexe de palladium II obtenu à partir de la forme déprotonnée de l'un de nos ligands imidazolium. De surcroît, nous avons mesuré la mobilité des porteurs de charge au sein de la mésophase. La partie mésogène des dérivés cationiques a été ajustée pour créer de nouveaux cristaux liquides ioniques fonctionnels, en vue de l'électrosynthèse de nanopaticules métalliques (par introduction de cyanométallates). La deuxième partie de cette thèse s'intéresse donc à l'électrocristallisation de nanoparticules d'or et d'argent en milieu liquide ionique auto-organisé. Les études montrent notamment qu'il est possible d'utiliser l'architecture supramoléculaire d'une mésophase pour influencer la morphologie des dépôts obtenus par électroréduction. Cette thèse présente enfin une nouvelle voie pour la synthèse de nanoparticules métalliques offrant un meilleur contrôle sur le processus de réduction que les méthodes chimiques traditionnelles.The first section of this thesis describes the synthesis of a new family of ionic liquid crystalline compounds based on imidazolium cations. The study focuses mainly on the mesomorphic behavior of these materials as a function of the molecule backbone (alkyl tail length). All compounds were fully characterized by polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction studies. We report also the synthesis, lamellar crystal structure and catalytic activity of the palladium (II) complex of the (deprotonated) carbene form of one of these salts. In addition, we measured the charged carrier mobilities in the mesophase. The molecular design of our ionic liquid crystalline materials has then been modified to incorporate cyanometallate to endow the products with electrochemical properties. The second section of this thesis is devoted to the development of a new route for the preparation of metallic nanoparticles by electrocrystallization. This approach allow direct and accurate control of the reduction process, of the size of the nanoparticles and of their density of nucleation on the substrate. Of particular significance is the demonstration herein that the supramolecular structure of the liquid-crystal phase can be used to influence the morphology of metal nanoparticles deposited by electrochemical reduction

Electrosynthèse de nanoparticules métalliques en milieu liquide ionique supramoléculaire

La première partie de cette thèse décrit comment l'introduction de groupements alkoxyphényles en position 1 et 3 d'une unité imidazolium induit des propriétés supramoléculaires à ce matériau liquide ionique. L'étude s'intéresse à l’évolution des propriétés mésomorphes en fonction des modifications structurales apportées (longueur de la chaîne aliphatique) en s'appuyant sur une caractérisation complète des phases cristal liquides (microscopie optique à lumière polarisée, calorimétrie différentielle, diffraction de rayons X). Nous nous sommes également intéressés à l'activité catalytique du complexe de palladium II obtenu à partir de la forme déprotonnée de l'un de nos ligands imidazolium. De surcroît, nous avons mesuré la mobilité des porteurs de charge au sein de la mésophase. La partie mésogène des dérivés cationiques a été ajustée pour créer de nouveaux cristaux liquides ioniques fonctionnels, en vue de l'électrosynthèse de nanopaticules métalliques (par introduction de cyanométallates). La deuxième partie de cette thèse s'intéresse donc à l'électrocristallisation de nanoparticules d'or et d'argent en milieu liquide ionique auto-organisé. Les études montrent notamment qu'il est possible d'utiliser l'architecture supramoléculaire d'une mésophase pour influencer la morphologie des dépôts obtenus par électroréduction. Cette thèse présente enfin une nouvelle voie pour la synthèse de nanoparticules métalliques offrant un meilleur contrôle sur le processus de réduction que les méthodes chimiques traditionnelles.The first section of this thesis describes the synthesis of a new family of ionic liquid crystalline compounds based on imidazolium cations. The study focuses mainly on the mesomorphic behavior of these materials as a function of the molecule backbone (alkyl tail length). All compounds were fully characterized by polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction studies. We report also the synthesis, lamellar crystal structure and catalytic activity of the palladium (II) complex of the (deprotonated) carbene form of one of these salts. In addition, we measured the charged carrier mobilities in the mesophase. The molecular design of our ionic liquid crystalline materials has then been modified to incorporate cyanometallate to endow the products with electrochemical properties. The second section of this thesis is devoted to the development of a new route for the preparation of metallic nanoparticles by electrocrystallization. This approach allow direct and accurate control of the reduction process, of the size of the nanoparticles and of their density of nucleation on the substrate. Of particular significance is the demonstration herein that the supramolecular structure of the liquid-crystal phase can be used to influence the morphology of metal nanoparticles deposited by electrochemical reduction

Bias and humidity effects on the ammonia sensing of perylene derivative/lutetium bisphthalocyanine MSDI heterojunctions

International audienceIn this paper, we prepared and studied sensors based on Molecular Semiconductor-Doped Insulator (MSDI) heterojunctions. These original devices are built with two stacked layers of molecular materials and exhibit very specific electrical and sensing properties. We studied the properties of a MSDI composed of the perylenetetracarboxylic dianhydride, PTCDA, or the fluorinated perylenebisimine derivative, C4F7-PTCDI, as n-type molecular material sublayers, and LuPc2 as a p-type semiconductor top layer. Their response to ammonia was compared to that of a resistor formed of only the top layer of the MSDI (LuPc2). Ammonia increases the current in the MSDIs whereas it causes a decrease in the case of LuPc2 resistors, as previously observed for other MSDIs with a n-type sublayer. At first, we showed the significant effect of the applied potential on the response of these sensors. There is an optimum operating point for which the response to ammonia is maximized, which depends on the nature of the samples. The influence of the thickness of the layers was studied, showing a strong influence of this parameter on the sensing properties. MSDIs prepared with fluorinated PTCDI exhibit a higher energy barrier and a lower current. Finally, in general, PTCDA/LuPc2 MSDIs show a strong response to ammonia with a response up to 250% to 30 ppm NH3 at 50% of relative humidity for the MSDI PTCDA/LuPc2 50 nm/50 nm. A discrimination better than 10 ppm between the ammonia concentrations was observed, regardless of relative humidity between 10 and 70% rh

Modulation of the organic heterojunction behavior, from electrografting to enhanced sensing properties

International audienceThe energy barrier of an organic heterojunction built on ITO electrodes and made from a low conductive sublayer (Cu(F16Pc)) covered by a highly conductive semiconductor (LuPc2) is modulated by electrografting of organic layers before depositing the sublayer. Impedance spectroscopy clearly demonstrates the increase of the energy barrier at the ITO – sublayer interface. Additionally, the electrografting is a versatile and promising method for the tuning of heterojunctions. The I(V) characteristics of the heterojunctions are highly modified by the electrografting. The same electromodifications of electrodes carried out on LuPc2 resistors lead to a modification of their transport properties too. The effect of the grafting of four different aromatic moieties bearing electron-donating and electron-withdrawing substituents is studied. One important feature is that the sensing properties are highly improved compared to the unmodified devices. Thus, the electrografting of dimethoxybenzene doubles the relative response of the heterojunction towards 90 ppm NH3, as well as the sensitivity in the range 1–9 ppm. This electrografting allows attaining a limit of detection as good as 140 ppb. The modified heterojunctions favorably compete other conductometric transducers for the detection of ammonia, at room temperature and in a broad range of relative humidity

Conducting Polymers for Ammonia Sensing: Electrodeposition, Hybrid Materials and Heterojunctions

International audiencePolyaniline (PANI) with electrodonating and electrowithdrawing substituents were electrodeposited and studied as sensing materials in resistors and heterojunctions. Whereas the dimethoxyaniline leads to a highly conductive material, the tetrafluoroaniline leads to a poor conducting polymer. However, this latter was used in heterojunctions, associated with a highly conductive material, the lutetium bisphthalocyanine LuPc2. Elsewhere, hybrid materials combining polypyrrole (PPy) with ionic macrocycles as counterions were also electrosynthesized and used as sensing material in resistors, for the detection of ammonia. They exhibit a higher sensitivity compared to PPy prepared with small counterions, with a stable response in a broad range of relative humidity

From the solution processing of hydrophilic molecules to polymer-phthalocyanine hybrid materials for ammonia sensing in high humidity atmospheres.

We have prepared different hybrid polymer-phthalocyanine materials by solution processing, starting from two sulfonated phthalocyanines, s-CoPc and CuTsPc, and polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), poly(acrylic acid-co-acrylamide) (PAA-AM), poly(diallyldimethylammonium chloride) (PDDA) and polyaniline (PANI) as polymers. We also studied the response to ammonia (NH3) of resistors prepared from these sensing materials. The solvent casted films, prepared from s-CoPc and PVP, PEG and PAA-AM, were highly insulating and very sensitive to the relative humidity (RH) variation. The incorporation of s-CoPc in PDDA by means of layer-by-layer (LBL) technique allowed to stabilize the film, but was too insulating to be interesting. We also prepared PANI-CuTsPc hybrid films by LBL technique. It allowed a regular deposition as evidenced by the linear increase of the absorbance at 688 nm as a function of the number of bilayers. The sensitivity to ammonia (NH3) of PANi-CuTsPc resistors was very high compared to that of individual materials, giving up to 80% of current decrease when exposed to 30 ppm NH3. Contrarily to what happens with neutral polymers, in PANI, CuTsPc was stabilized by strong electrostatic interactions, leading to a stable response to NH3, whatever the relative humidity in the range 10%-70%. Thus, the synergy of PANI with ionic macrocycles used as counteranions combined with their simple aqueous solution processing opens the way to the development of new gas sensors capable of operating in real world conditions

On the interest of ambipolar materials for gas sensing

International audienceBased on the electrochemical properties of a series of metallophthalocyanines this article shows that the phthalocyanine bearing four alkoxy groups and twelve fluorine atoms behaves approximately as those with eight fluorine atoms. This indicates that the electron-donating effect of one alkoxy group balances the electro-withdrawing effect of one fluorine atom. We engaged three metallophthalocyanines, namely the octafluoro copper phthalocyanine, Cu(F8Pc), an octaester metallophthalocyanine and a phthalocyanine bearing four alkoxy groups and twelve fluorine atoms, Zn(T4F12Pc), in building original conductometric transducers that are Molecular Semiconductor – Doped Insulator heterojunctions (MSDIs) in association with the highly conductive lutetium bisphthalocyanine, LuPc2. Whereas the octaester derivative and Zn(T4F12Pc) exhibited a negative response to ammonia, as expected for p-type materials, Cu(F8Pc) exhibited a particular behavior. At low humidity levels, 30 and 10% rh, the current of the Cu(F8Pc)/LuPc2 MSDI decreases, similarly to p-type devices, but at higher relative humidity values, 70% rh, the current increases under ammonia, which is the signature of a n-type behavior. This ambipolar behavior is unique amongst semiconducting sensing materials. This work opens the way to the study of ambipolar materials as sensing materials for the development of a new type of conductometric gas sensors

Synthesis and characterization of fluorophthalocyanines bearing four 2-(2-thienyl)ethoxy moieties: from the optimization of the fluorine substitution to chemosensing

International audienceThe energy levels of the HOMO/LUMO Frontier orbitals and the electronic properties of phthalocyanine macrocycles can be tuned by the introduction of substituents. Starting from tetrafluorophthalonitrile, we studied the substitution of fluorine atoms by (2-thienyl)ethoxy moieties. An optimization of the experimental conditions (nature and stoichiometry of the alcohol and base, temperature) allowed us to obtain the monoalkoxy derivative with a very good yield. It was fully characterized using 19F and 1H NMR spectroscopies, thermal analysis and X-ray diffraction on single crystals. Then, the corresponding zinc phthalocyanine was synthesized, characterized by means of 19F and 1H NMR spectroscopies, thermal analysis, and also by electronic spectroscopy and electrospray mass spectrometry. The unsymmetrical zinc phthalocyanine bearing also four (2-thienyl)ethoxy moieties was prepared by the mixed condensation of the tetraalkoxyphthalonitrile with the tetrafluorophthalonitrile. The phthalocyanines were used to build an electronic device, a p-type Molecular Semiconductor – Doped Insulator heterojunction (MSDI), in combination with the lutetium bisphthalocyanine as a molecular semiconductor, and their chemosensing behavior towards ammonia was studied

A Comprehensive Study of Poly(2,3,5,6-tetrafluoroaniline): From Electrosynthesis to Heterojunctions and Ammonia Sensing

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Low Conductive Electrodeposited Poly(2,5-dimethoxyaniline) as a Key Material in a Double Lateral Heterojunction, for Sub-ppm Ammonia Sensing in Humid Atmosphere

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