Stephane Mery | Centre National de la Recherche Scientifique / French National Centre for Scientific Research (original) (raw)

Papers by Stephane Mery

$Research paper thumbnail of <title>Role of the polymer viscoelasticity on the orientational processes of chromophores and on the photorefractive performances in low T<formula><inf><roman>g</roman></inf></formula>-doped polymers</title>$

Organic Photorefractive and Photosensitive Materials for Holographic Applications, 2002

$Research paper thumbnail of <title>New results on low-T<formula><inf><roman>g</roman></inf></formula> photorefractive materials</title>$

Xerographic Photoreceptors and Organic Photorefractive Materials IV, 1998

J. Mater. Chem. A, 2015

The synthesis and characterization of a series of dumbbell-shaped molecules constructed from para... more The synthesis and characterization of a series of dumbbell-shaped molecules constructed from paraffinfree central dyes linked to two triazatruxene (TAT) units are described. The photovoltaic properties of these new glassy electron-donating molecules in a bulk heterojunction with fullerene derivatives have been studied. For this series of molecules, the local-range molecular packing in the amorphous solid state is mainly influenced by the TAT units bearing bulky side-chains, while the optical properties and energy levels are tuned by the choice of the central core. Therefore, TAT acts as a structuration platform in thin films for pure or blended active layers and independently, the optoelectronic properties are driven by the choice of the central dye. Photovoltaic cells based on these materials exhibited power conversion efficiencies of up to 3.5%, among the top values reported so far for soluble amorphous small molecule based organic photovoltaic devices. These TAT-based derivatives are a promising platform to reach high solar cell efficiencies as well as to understand in detail the impact of the chemical structure on the optoelectronic properties. Scheme 2 Synthetic pathway for the preparation of the TAT-based chromophores. (i) K 2 CO 3 , Pd 2 (dba) 3 , P(o-tolyl) 3 , toluene/1,4-dioxane, reflux. 6622 | J. Mater. Chem. A, 2015, 3, 6620-6628 This journal is

Liquid Crystals, 1997

Novel liquid crystalline Low Molecular Mass ( LMM ) materials bearing two chiral lactate groups, ... more Novel liquid crystalline Low Molecular Mass ( LMM ) materials bearing two chiral lactate groups, as well as compounds of like structure to M HPOBC have been synthesized. All the LMM compounds exhibit the SmC * A (antiferroelectric) and/or SmC * c (ferrielectric) phases. The mesogens have been incorporated as pendant groups on polymer backbones of three diVerent natures to prepare side chain liquid crystalline copolysiloxanes, homopolysiloxanes and homopolyacrylates. The investigation of the polymers by means of miscibility studies showed that the antiferro-and ferri-electric phases are strongly destabilized in the coposiloxanes and homopolysiloxanes, while in the homopolyacrylates a large temperature range mesophase is found to be miscible with the SmC * A phase. The physical properties of the mesophases and their stability, both for the LMM materials and the polymers, are presented and discussed.

International Photonics and OptoElectronics, 2015

$Research paper thumbnail of <title>Bifunctional dimer and polymers for photorefractive applications</title>$

Xerographic Photoreceptors and Organic Photorefractive Materials II, 1997

ABSTRACT We present the electro-optic, photoconductive and photorefractive characterization of a ... more ABSTRACT We present the electro-optic, photoconductive and photorefractive characterization of a novel organic photorefractive structure. It is composed of a bifunctional dimeric molecule combining both photoconduction and electro-optic properties. This low molecular weight material is a glass, showing a glass transition temperature (Tg) at 27 degrees C. Doped with (2,4,7-trinitro-9-fluorenylidene)malononitrile (TNFDM) as photosensitizer (1% wt), this dimer exhibits 200 cm-1 photorefractive gain at 633 urn for 50 V μm-1 electric field applied. Compared to usual doped polymers which generally show inhomogeneities in the mixtures, this material presents good optical quality thanks to its monophasic character. A serie of functionalized copolymer has also been synthesized, in which the ratio of the chromophore moieties over the charge carrier moieties was varied. These copolymers show photoconductivity but no photorefractivity.

$Research paper thumbnail of <title>Optimization of the efficiencies of photorefractive polymers: correlations between visoelastic properties and electro-optical responses</title>$

Materials, Devices, and Systems for Display and Lighting, 2002

ABSTRACT The photorefractive properties of low glass transition temperature (Tg) doped polymers a... more ABSTRACT The photorefractive properties of low glass transition temperature (Tg) doped polymers are essentially ruled by the ability of the push-pull chromophores to align along the electric field. Therefore,a high rotational mobility is therefore needed for these non linear optical chromophores incorporated in the matrix. However, even if the influence of Tg on the photorefractive performances of guest-host polymers has been previously pointed out, this unique parameter is not sufficient to take into account the viscoelastic properties of the matrices. A complete study of the orientational dynamics of chromophores in various low Tg doped polymers, investigated by dielectric spectroscopy, second harmonic generation and electrooptical dynamical measurements, is presented. The results are fully interpreted and modeled by rheologic laws used to describe the viscoelastic behavior of polymers. Finally, the influence of the average molecular weight is also analyzed and then demonstrates the interest of using low molecular weight polymers.

Journal of Materials Chemistry, 2001

In this paper, we considered the case of low molecular weight bimesogenic liquid crystals contain... more In this paper, we considered the case of low molecular weight bimesogenic liquid crystals containing a siloxane moiety as the central part of their molecular architecture. For some of these compounds, both ferro-and antiferroelectric mesophases are present. Two distinct smectic structures can develop as a function of temperature, the first one at high temperature corresponding to a synclinic molecular arrangement with elongated molecules, and the second one at lower temperature corresponding to an anticlinic organisation with V-shaped molecules. Numerical calculations of the energy of different conformations of these bimesogenic molecules presented here indicate that there is no difference in energy between V-shaped and linear conformations regardless of the number of silicon atoms in the siloxane moiety. Thus a microscopic model of the synclinic-anticlinic phase transition is developed where the driving force is indeed a free energy difference between the two phases, and not a difference of energy between the V-shaped and linear conformations. The model explains why the anticlinic SmC A phase is more stable than the synclinic SmC one, why the synclinic SmC phase is generally the higher temperature one, and why in some organosiloxane materials the anticlinic SmC A phase is not present.

Linear and Nonlinear Optics of Organic Materials II, 2002

ABSTRACT In photorefractive guest-host polymers, fast orientational dynamics of push-pull chromop... more ABSTRACT In photorefractive guest-host polymers, fast orientational dynamics of push-pull chromophores are needed to obtain the so-called orientational enhancement as well as high performances. For this purpose, a better understanding of the relationships between viscoelastic properties of polymers. and orientational processes of chromophores is now essential for the optimization and the development of new efficient photorefractive polymers. In the present investigation, the orientational dynamics of the chromophores are probed in details by dielectric spectroscopy, second-harmonic generation and ellipsometric techniques, in various doped polymers. The materials are based on a polyvinylcarbazole plasticized with N-ethyl carbazole, a polysiloxane functionnalized with a carbazole pendant, as Well as polystyrenes with different average macromolecular weights. The temperature-dependencies of their dielectric and electro-optic responses provide information on the rotational mobility of the chromophores at a microscopic scale. These data are directly compared to the temperature-dependence of the viscoelastic properties, characterized at a macroscopic level by shear compliance measurements. The analysis reveals the strong coupling between the orientational processes of the chromophores and the polymer chain dynamics, The effects of other physical parameters (applied voltage magnitude, amount of plasticizer, average molecular weight of the polymer host) on the orientational dynamics of chromophores are also investigated in order to describe the mechanical interactions between the chromophores and the polymer host. Finally, a new way of optimization for photorefractive polymeric material properties is suggested.

The Journal of Physical Chemistry B, 2004

We have studied the behavior of a low molecular mass organosiloxane ferroelectric liquid crystal ... more We have studied the behavior of a low molecular mass organosiloxane ferroelectric liquid crystal at the air-water interface. Data obtained with Langmuir isotherms, surface potential measurements, and Brewster angle microscopy are presented and discussed. The compound forms films on the Langmuir trough, with phase transitions to multilayers upon compression. As seen with Brewster angle microscopy, the monolayers are optically isotropic whereas striking birefringent structures develop in the multilayer films. These periodic structures result from a surface elasticity phenomenon.

Physical Chemistry Chemical Physics, 2012

Ultrafast transient absorption spectroscopy is performed on a novel donor-acceptor-donor triad ma... more Ultrafast transient absorption spectroscopy is performed on a novel donor-acceptor-donor triad made of two identical bisthiophene derivatives as electron donors and a central perylenediimide moiety as electron acceptor. The triad is extended at both ends by covalently bound siloxane chains that confer self-organisation into thin smectic films at ambient temperature. When diluted in chloroform, selective excitation of the donor moiety leads to resonance energy transfer within 130 fs to the acceptor moiety, followed by the formation of a charge transfer (CT) state in B3 ps. The CT state recombines entirely on a 55 ps time scale. In the liquid crystal films, excitonic intermolecular coupling leads to significant changes in the dynamics. Most remarkably, ultrafast intra-and intermolecular CT state formation occurs in about 60 fs, i.e. on a time scale comparable to electronic coherence times. While the intra-molecular CT states recombine on the same time scale as in solution or even faster, inter-molecular CT states live for about 1 ns. Last, triplet states of the perylenediimide moiety dominate the differential absorption after B1 ns. We anticipate that the fast recombination of intra-molecular CT states and the triplet state formation may severely limit the photo-current in these materials.

Optics Express, 2007

We report on the creation of micro-patterns in an oriented nematic elastomer (an artificial muscl... more We report on the creation of micro-patterns in an oriented nematic elastomer (an artificial muscle material) by photopolymerization of surface aligned nematic liquid crystal monomers. We demonstrate that microscopic techniques are able to create accurate patterns in rubber-like liquid crystal materials. Two approaches, based on one and two-photon excitations respectively, are implemented using a microscope-based setup. Due to its high spatial selectivity, the two-photon excitation mode yields finer patterns. Benefitting from the intrinsic, thermally-induced, contractile properties of the material, gratings with variable steps in response to temperature changes were fabricated.

$Research paper thumbnail of Low-Tg Photorefractive Materials Based on Bifunctional Molecules$

Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals, 1998

Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals, 1997

Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals, 1993

... ER 11, Str. des 17. Juni 135, 0-1000 Berlin 12, Germany and S. MERY and R. SHASHIDHAR Center ... more ... ER 11, Str. des 17. Juni 135, 0-1000 Berlin 12, Germany and S. MERY and R. SHASHIDHAR Center for BiolMolecular Science and Engineering, Code 6090, Naval Research Laboratoty, Washington, DC 20375-5000, U. SA (Received June 15, 1992) ...

Macromolecules, 1995

The synthesis and mesomorphic properties of a series of ferroelectric liquid crystalline polysilo... more The synthesis and mesomorphic properties of a series of ferroelectric liquid crystalline polysiloxanes bearing chiral4-[(4-((n-alkyloxy)sulfinyl)phenyl)ethynyllphenyl4-(undecyloxy)benzoate as mesogenic pendant groups are presented. In these polymers, the chirality is introduced via an asymmetric sulfur atom. The synthesis of the materials was possible through three successive polymer-analogous reactions. The last key synthetic step is the polyesterification of the poly((undecy1oxy)benzoic acidmethylsiloxane) with the n-alkyl4-[(4-hydroxyphenyl)ethynyllbenzenesulfinate derivatives, which could be carried out efficiently. Up to 97% overall substitution rates of the siloxane units by the mesogenic moiety could thus be obtained. In this paper are also reported the results of the preliminary investigations of the ferroelectric properties, carried out in the SC* phase of one polymer. Finally, the comparison of the mesomorphic properties of a sulfinate-based polymer and molecule with their carboxylate-based counterparts is briefly reviewed.

Macromolecules, 2007

Recently, controlled radical polymerization techniques have been performed by some authors to pol... more Recently, controlled radical polymerization techniques have been performed by some authors to polymerize dendronized (meth)acrylic monomers. 8g,15-17 The polymerization techniques used were atom transfer radical polymerization (ATRP) 8g,15,16 and reversible addition ...

Macromolecules, 2003

The dynamics of the electrooptic and dielectric properties in low-Tg photorefractive guesthost po... more The dynamics of the electrooptic and dielectric properties in low-Tg photorefractive guesthost polymers are directly related to the orientational dynamics of doping nonlinear optical chromophores. We report on experimental results on the orientational mechanisms of chromophores above T g, investigated by ellipsometry and dielectric spectroscopy. These measurements have been performed on plasticized poly(N-vinylcarbazole) and polysiloxane functionalized with a carbazole pendant, doped with nonlinear optical chromophores. The data are compared to the mechanically measured complex shear compliance of the materials. The results of this comparison demonstrate that the orientational dynamics of chromophores are entirely ruled by the viscoelastic properties of the polymer matrix. In addition, the influence of the chromophore size is investigated and interpreted by using free volume and rheological laws. Finally, the evidence of an anelastic memory, induced by the orientation of the chromophores below T g, is pointed out. † Groupe d'Optique Non Linéaire et d'Optoélectronique. ‡ Groupe des Matériaux Organiques.

Macromolecules, 2000

Wormlike dendrimers made of flexible and noninteracting segments were synthesized. Starting from ... more Wormlike dendrimers made of flexible and noninteracting segments were synthesized. Starting from a poly(methylhydrosiloxane) G0 and using short propylsilane branches, the synthesis did not go beyond the second generation, as predicted from steric congestion. The starting polymer and the G1 and G2 dendrimers synthesized were studied by small-angle neutron scattering. The molecular-weight dependence of their radius of gyration (Rg ∝ M ν , ν growing from 0.53 for G0 to 0.94 for G2) showed the backbone conformation to go from very flexible for G0 to nearly rodlike for G2. This was supported by the growth of the persistence length from 12 to over 200 Å, as deduced from an analysis of the data according to Benoît-Doty's law. The dendrimers being made of flexible parts, their stretching was attributed to the congestion of the peripheral branches. The absence of liquid crystallinity was imputed to the dynamical flexibility of the molecules.