Marcel Bouvet

Tuning the semiconducting nature of bis(phthalocyaninato) holmium complexes via peripheral substituents

The semiconducting properties of the heteroleptic and homoleptic bis(phthalocyaninato) holmium complexes bearing electron-withdrawing phenoxy substituents at the phthalocyanine periphery, namely Ho(Pc)[Pc(OPh)8] (1) and Ho[Pc(OPh)8]2 (2) [Pc = unsubstituted phthalocyaninate; Pc(OPh)8 = 2,3,9,10,16,17,23,24-octaphenoxyphthalocyaninate] have been investigated comparatively. Using a solution-based Quasi–Langmuir–Shafer (QLS) method, the thin solid films of the two compounds were fabricated. The structure and properties of the thin films were investigated by UV-vis absorption spectra, X-ray diffraction (XRD) and atomic force microscopy (AFM). Experimental results indicated that H-type molecular stacking mode with the common preferential molecular “edge-on” orientation relative to the substrate has been formed, and the intermolecular face-to-face π–π interaction and film microstructures are effectively improve by increasing the number of phenoxy substituents of the Pc periphery within the double-decker complexes. The electrical conductivity of Ho(Pc)[Pc(OPh)8] films was measured to be approximately 4 orders of magnitude larger than that of Ho[Pc(OPh)8]2 films, indicating significant effect of peripheral electron-withdrawing phenoxy groups on conducting behaviour of bis(phthalocyaninato) holmium complexes. In addition, the gas sensing behaviour of the QLS films of 1 and 2 toward electron donating gas, NH3, was investigated in the concentration range of 15–800 ppm. Surprisingly, contrary responses towards NH3 were found for the QLS films of 1 and 2. In the presence of NH3, the conductivity of the films of Ho(Pc)[Pc(OPh)8] (1) decreased while the conductivity of the films of Ho[Pc(OPh)8]2 (2) increased. This observation clearly demonstrated the p- and n-type semiconducting nature for 1 and 2, respectively. Furthermore, compared to the heteroleptic 1 having a hole mobility of 1.7 × 10−4 cm2 V−1 s−1, homoleptic 2 exhibits an electron mobility as high as 0.54 cm2 V−1 s−1. Therefore, the inversion of the semiconducting nature of the double-deckers from p- to n-type can be successfully and easily realized just by increasing the number of peripheral phenoxy groups attached to the conjugated Pc cores.

Elaboration of ammonia gas sensors based on electrodeposited polypyrrole—Cobalt phthalocyanine hybrid films

The electrochemical incorporation of a sulfonated cobalt phthalocyanine (sCoPc) in conducting polypyrrole (PPy) was done, in the presence or absence of LiClO4, in order to use the resulting hybrid material for the sensing of ammonia. After electrochemical deposition, the morphological features and structural properties of polypyrrole/phthalocyanine hybrid films were investigated and compared to those of polypyrrole films. A gas sensor consisting in platinum microelectrodes arrays was fabricated using silicon microtechnologies, and the polypyrrole and polypyrrole/phthalocyanine films were electrochemically deposited on the platinum microelectrodes arrays of this gas sensor. When exposed to ammonia, polymer-based gas sensors exhibited a decrease in conductance due to the electron exchange between ammonia and sensitive polymer-based layer. The characteristics of the gas sensors (response time, response amplitude, reversibility) were studied for ammonia concentrations varying from 1 ppm to 100 ppm. Polypyrrole/phthalocyanine films exhibited a high sensitivity and low detection limit to ammonia as well as a fast and reproducible response at room temperature. The response to ammonia exposition of polypyrrole films was found to be strongly enhanced thanks to the incorporation of the phthalocyanine in the polypyrrole matrix.

Microstructured electrodeposited polypyrrole–phthalocyanine hybrid material, from morphology to ammonia sensing

Hybrid materials combining polypyrrole with ionic macrocycles as counterions are electrosynthesized at the surface of platinum interdigitated electrodes. The chemical composition of the hybrid films is characterized by infrared reflexion absorption spectroscopy (IRRAS) and glow discharge optical emission spectroscopy (GDOES) and their morphology is studied by a range of techniques such as optical topomicroscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The obtained films reveal to be more homogeneous, with smaller crystallites, compared to polypyrrole synthesized with small counterions. Finally, the films exhibit a higher sensitivity to ammonia, with a very good reversibility and with a stable response in a broad range of relative humidity. Overall, we present the advantages of combining ionic phthalocyanines with polypyrrole in enhancing the properties of the final material. Synergetic effects in the structure and properties of polypyrrole–phthalocyanine materials open the way to their development in the field of hybrid material and their use in chemosensing.

Morphology controlled nano-structures of an octa(phenoxy)-substituted phthalocyaninato zinc complex: solvent effect on the self-assembly behaviour

The 2,3,9,10,16,17,24,25-octakis(phenoxy)phthalocyaninato zinc, (Zn[Pc(OPh)8]) was fabricated into nano-/micro-structures via solution-phase self-assembly. The self-assembling properties of Zn[Pc(OPh)8] in coordinating and non-coordinating solvents (methanol and n-hexane) have been comparatively studied by electronic absorption, fluorescence, Fourier transform infrared spectroscopy (FT-IR), scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) techniques. The conducting properties were evaluated by current–voltage (I–V) measurements. Due mainly to the presence of different intermolecular Zn–O coordination interactions between the Zn[Pc(OPh)8] molecules in n-hexane and between the Zn[Pc(OPh)8] and solvent molecules in methanol, the self-assembly of the Zn[Pc(OPh)8] results in nano-/micro-structures with distinctly different morphology as follows: nanobelts in n-hexane, and soft nano-sticks, microscale needle mushroom as well as pine leaves in methanol depending on aggregation time. The size and/or morphological evolution of the nanostructures have been clearly revealed during the self-assembly process. The present result appears to represent the first effort toward realization of controlling and tuning the biomorphs of self-assembled nanostructures of phthalocyanine-related complexes through the solvent coordinating effect. Furthermore, both nanobelts and micrometer-sized pine leaves were revealed to show good semiconductor features.

Experimental and theoretical study of electronic structure of lutetium bi-phthalocyanine.

Using Near Edge X-Ray Absorption Fine Structure (NEXAFS) Spectroscopy, the thickness dependent formation of Lutetium Phthalocyanine (LuPc2) films on a stepped passivated Si(100)2×1 reconstructed surface was studied. Density functional theory (DFT) calculations were employed to gain detailed insights into the electronic structure. Photoelectron spectroscopy measurements have not revealed any noticeable interaction of LuPc2 with the H-passivated Si surface. The presented study can be considered to give a comprehensive description of the LuPc2 molecular electronic structure. The DFT calculations reveal the interaction of the two molecular rings with each other and with the metallic center forming new kinds of orbitals in between the phthalocyanine rings, which allows to better understand the experimentally obtained NEXAFS results.

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.

Effects of metal–ligand coordination on the self-assembly behaviour of a crown ether functionalised perylenetetracarboxylic diimide

A novel perylenetetracarboxylic diimide (PDI) derivative, N,N′-di(4′-benzo-15-crown-5-ether)-1,7-di(4-tert-butyl-phenoxy)perylene-3,4;9,10-tetracarboxylic diimide (CRPDI), has been synthesised and characterised. Dimerisation of CRPDI is induced by the presence of K+ in CHCl3 or spontaneously occurs in methanol, as revealed by absorption and emission spectroscopy. In particular, the formation of co-facial dimer in the presence of K+ proceeds in a three-stage process, as indicated by absorption spectroscopy. The belt- and rope-like nanostructures of CRPDI fabricated from methanol and CHCl3 solution in the presence of K+ are obtained by scanning electron microscopy. Furthermore, the conductivity of the rope-like nanostructures from the cation-induced dimeric species is more than ca. 1 order of magnitude higher than the belt-like nanostructures from the solvent-induced dimeric species. The present result represents the further effort towards realisation of controlling and tuning the morphology of self-assembled nanostructures of PDI derivatives through molecular design and synthesis. It will be valuable for the design and preparation of PDI-based nano-(opto)electronic devices with good performance due to the close relationship between the molecular ordering and dimensions of nanostructures and the performance of nanodevices.

Electrochemical detection of the 2-isobutyl-3-methoxypyrazine model odorant based on odorant-binding proteins: The proof of concept

We developed an electrochemical assay for the detection of odorant molecules based on a rat odorant-binding protein (rOBP3). We demonstrated that rOBP3 cavity binds 2-methyl-1,4-naphtoquinone (MNQ), an electrochemical probe, as depicted from the decrease of its electrochemical signal, and deduced the dissociation constant, KdMNQ=0.5(±0.2)μM. The amount of MNQ displaced from rOBP3 by 2-isobutyl-3-methoxypyrazine (IBMP), a model odorant molecule, was measured using square-wave voltammetry. The release of MNQ by competition led to an increase of the electrochemical response. In addition, this method allowed determination of the dissociation constant of rOBP3 for IBMP, KdIBMP=0.5(±0.1)μM. A negative control was performed with a non-binding species, caffeic acid (CA). The determined binding affinity values were confirmed using a fluorescent competitive binding assay and isothermal titration microcalorimetry. This electrochemical assay opens the way for designing robust, reliable and inexpensive odorant biosensors.

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

The 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.

Humidity Insensitive Conductometric Sensors for Ammonia Sensing

Interest in molecular materials has been driven in large part by their various and prosperous applications, especially in the domain of organic electronics, where they offer many advantages as well as alternative approaches compared to their inorganic counterparts. Most of conductometric transducers are resistors[[ and transistors[[[, but rarely diodes[6]. In our laboratory, we designed and characterized new molecular material based devices. Molecular Semiconductor Doped Insulator (MSDI) heterojunctions were built around a heterojunction between a Molecular Semiconductor (MS) and a Doped Insulator (DI)[7][8]. This new device exhibits interesting electronic properties that allow ammonia sensing in a large humidity range at room temperature.