The use of carbon-based materials in electrochemical double-layer supercapacitors (EDLC) is currently being the focus of much research. Even though activated carbon (AC) is the state of the art electrode material, AC suffers from some drawbacks including its limited electrical conductivity, the need for a binder to ensure the expected electrode cohesion and its limited accessibility of its pores to solvated ions of the electrolyte. Owing to their unique physical properties, carbon nanotubes (CNTs) or graphene could overcome these drawbacks. It has been demonstrated that high specific capacitance could be obtained when the carbon accessible surface area of the electrode was finely tailored by using graphene combined with other carbonaceous nanoparticles such as CNTs12.In this work, to further increase the specific capacitance of the electrode, we have covalently grafted onto the surface of single-walled carbon nanotubes (SWCNTs), exfoliated graphite or graphene oxide (GO), anthraquinone (AQ) derivatives which are electrochemically active materials. The modified SWCNTs and graphene-like materials have been characterized by Raman spectroscopy, X-ray photoemission and cyclic voltammetry . Then suspensions based on mixtures of modified SWCNTs and modified graphene-like materials have been prepared and transformed into electrodes either by spray coating or by filtration. These electrodes have been characterized by SEM and by cyclic voltammetry in 0.1M H2S04 electrolyte.
The Copper(I)-catalyzed Azide-Alkyne Cycloaddition (CuAAC) has been investigated as a versatile synthetic
pathway to graft highly chemically sensitive "push-pull" chromophores onto a polymer backbone. We
demonstrate that the CuAAC is highly efficient in mild conditions, chemioselective and is a powerful tool to
design new powerful organic NLO side-chain copolymers.
In the first part of this paper, we use a specially developed sensitive polymer (PLG) which belongs to the polysiloxane family. Thin layers of this polymer are deposited onto the surface of the optical transducers. Results will be presented on the response of diffraction-based optical transducers such as gratings and also on interferometric transducers and especially integrated Mach-Zehnder (MZ) interferometers. In the first case, a relief grating is coated with the sensitive polymer. A small variation of the refractive index of this layer, due to the presence of pollutant, induces a variation of the intensity of the diffracted orders which can be measured. In the second case, one arm of the integrated MZ interferometers is coated with the polymer. The variation of the refractive index of the polymer causes a phase shift in the measuring arm which can be measured by the modification of the output intensity. Assessment of sensitivity for the detection of nitro-aromatic compounds using a PLG sensitive layer on both sensors are presented and are also compared to the response of a SAW-based sensor coated with the same polymer.
In the second part of this paper, synthesis, spectroscopy and fluorescence quenching behaviour of a N-(2,5-ditertio-butylphenyl)-1,8-naphthalimide functionalised polystyrene (PST-NI) are reported. PST-NI was synthesized by free radical polymerisation of the corresponding monomer. The molecular weight (Mn) is 43 000 g.mol-1. Introduction of a bulky moiety on the naphthalimide chromophores avoids P-stacking of the polymer side chains as well as excimer formation and hence leads to very high fluorescence quantum yields in thin solid films (up to 60%). Upon 1 minute exposure to DNT vapour, it was shown that a 5.5 nm thick film of PST-NI exhibits a 45% drop in its fluorescence intensity, which makes this polymer very attractive for sensing applications.
The synthesis, spectroscopic characterization and fluorescence quenching efficiency of a polymer (PSt-NI) and a low molecular weight molecule (NI) containing the 4-(N, N disubstituted)amino-N-2,5ditertiobutylphenyl-1,8-naphthalimide chromophore are reported. Similar spectroscopic properties of thin films and solutions are observed. This is consistent with the absence of interactions between polymer side chains. The absorption and fluorescence spectra of PSt-NI studied in various solvents of different polarity are compared to the corresponding spectra of NI. The longest wavelength absorption of PSt-NI and NI is characterized by a band with a maximum wavelength around 410 nm. The peak position is sensitive to the polarity of the solvent, which is in agreement with the charge transfer character of the transition. The fluorescence spectrum of PSt-NI shows a maximum emission in chloroform at 515 nm and is red shifted compared to those of NI. Fluorescence lifetimes of PSt-NI and NI are measured in presence and absence of 2,4-dinitrotoluene (DNT) and the results are interpreted via the Stern-Volmer analysis. In solution, the fluorescence quenching of NI is purely collisional, whereas both dynamic and static quenching are observed with PSt-NI Upon 1 minute exposure to DNT vapor, it was shown that a 5 nm thick film of PSt-NI exhibited a 45% drop in its fluorescence intensity, which makes this polymer very attractive for sensing applications.
Recent years have seen considerable interest in the possibility of using rare earth chelates as emissive materials in organic media. Lanthanides luminescence is quite interesting in applications requiring high spectral purity (for example in OLEDs), or infra red luminescence, in active optical waveguides for telecommunications. The use of organic optical amplification modules is attractive for their ease of fabrication, and therefore their potential low cost, but the high losses at NIR wavelength and the limitation of the emission lifetime due to the quenching effect of the organic matrix greatly limits their performances. However, rare earth chelates offer the possibility to reduce by several orders of magnitude the pump power needed for population inversion, using the absorption of the organic ligand followed by an energy transfer to the rare earth ion. By choosing a ligand with a high molecular absorption, it should then be possible to balance the short emission lifetime and hence to obtain optical amplification. We report on the synthesis and characterisation of the optical near infrared properties of an erbium phthalocyanine. The complex shows very high absorption in the 670nm region, is highly soluble and shows minimum concentration quenching effect. The red absorption could allow the use of standard laser diode as pump source in a planar polymer amplifier device.
Electro-optical properties of polymer dispersed liquid crystal (PDLC) or holographic polymer dispersed liquid crystal (H-PDLC) are very sensitive to the photoinduced phase separation process (PIPS). In order to improve initial mixture and recording setup, real time monitoring of diffraction efficiency is currently performed using
a diffusion model based on the moderation Fick's law. Nevertheless, this model does not take into account neither change of affinity for liquid crystal molecules when the monomer polymerization occurs nor the droplets morphology observed by scanning electron microscopy. In this paper, a new model consistent with the general Onsager theory of transport is introduced. As an application, droplet's growth and spatial response of H-PDLC films are described using dimensionless numbers and very general normalized parameters which open new method
of improvement for electro-optical devices based on PDLC's or H-PDLC's.
A series of 4-aminonaphthalimide functionalized polymers has been synthesized. They differ by the nature of their backbone: and by the nature of the substituent at the imide nitrogen atom. The absorption and emission properties of these polymers have been investigated. Photoluminescence quantum yields in the solid state up to 35 percent were observed. Cyclic voltammetry in conjunction with UV-visible spectrometry have been performed in order to determine the HOMO and LUMO energy levels of the different materials. Electroluminescent devices were fabricated with these polymers as emitting layers, and ITO and Ca as anode and cathode, respectively. Monolayer devices showed a limited performance. Efficient green light emission was obtained with a bilayer device based on PVK as a hole transport material and a polystyrene derivative as an emitting layer. A maximum luminance of 7100cd/m2 was obtained under 16V. The device had a maximum external quantum efficiency of 1 percent and a maximum external energetic efficiency of 0.2 percent. Doping PST-NI-BuP with 20 percent DCM resulted in red-orange emission with a brightness as high as 1800 cd/m2. Doping PST-NI-BuP with 20 percent DCM resulted in red-orange emission with a brightness as high as 1800 cd/m2. Moreover, this study showed a strong influence of the chemical environment of the naphthalimide moiety on the photoluminescence and electroluminescent properties of the polymers.
We report the fabrication of efficient green light-emitting diodes using a side-chain polymer based on a high-electron affinity (EA) naphtalimide moiety (PNI). The chromophore is attached to a polymethacrylate backbone through a spacer, and emits in the green with high efficiency. In single-layer light-emitting diodes (LEDs), we find that the electroluminescence (EL) efficiency is not limited by Al cathodes as for poly(p-phenylene-vinylene), PPV, and we attribute this to the increased EA. We report maximum internal efficiencies of about 1.7 percent for Ca and 0.9 percent for Al in double-layer devices where PPV serves as both Hole-injector and emitter. Compared to some oxadiazole based electron injection/transport layer, PNI gives higher efficiencies at high currents, and longer lifetimes. Tuning of emission in the red is possible by dye-doping the PNI and causing the emission to happen in this layer. We discuss the properties of the different device configurations with a view to the electronic structure of the materials and in particular to the influence of the thickness of the individual layers on efficiency and driving conditions.
The considerably interest in the possibility of fabricating efficient optical limiters based on solid-state materials have led us to develop an easy method for producing RSA compound doped in PMMA. The chosen RSA dye was a soluble silicon phthalocyanine (SiPc(OC7H15)). By comparing the non linear absorption of this compound in solution in THF and in PMMA, we show that broadband solid-state limiters can be made with such a dye for visible nanosecond-pulse excitation. The importance of broadband criterion such as the photopic transmission to adjust the transmission at low incident energy in conjunction with the color neutrality are also stressed.
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