The synthesis, spectroscopic characterization and complexing properties of calixarene-based fluorescent
sensors are reported. The calixarene bearing four dansyl fluorophores (Calix-DANS4) exhibits a very high affinity for
the detection of lead. A fluorimetric micro-device based on the use of a Y-shape microchannel was developed and
allows lead detection with a 5 ppb detection limit. For mercury detection, a fluorescent molecular sensor containing a
calixarene anchored with four 8-quinolinoloxy groups (Calix-Q) has been synthesized. The absorption and fluorescence
spectra of this sensor are sensitive to the presence of metal cations. An efficient fluorescence quenching is observed
upon mercury complexation because of a photoinduced electron transfer from the fluorophore to the bound mercury.
Calix-Q shows a high selectivity towards Hg2+ over interfering cations (Na+, K+, Ca2+, Cu2+, Zn2+, Cd2+ and Pb2+) and a
70 ppb sensitivity.
New fluorinated poly(arylene ether sulfone)s (FPAES) and poly (arylene ether ketone)s (FPAEK) with two types of NLO chromophores as pendant groups were obtained by a polycondensation reaction carried out using very mild reaction conditions. The glass transition temperature (Tg) of these copolymers is between 168 and 190°C. The SHG intensity was measured during thermal corona poling : the dipole orientation starts at 100°C, and reaches a maximum at 160°C, which is lower than Tg. During cooling of the film under the applied electric field, we observed an unusual drop of the SHG intensity starting at 120°C and reaching 70 % of the maximum value. The physical origin of this drop has been investigated and is possibly attributable to a secondary phase transition of the copolymers. Despite this decrease, d33 coefficients measured after poling vary between 2 and 15 pm/V at 1907 nm fundamental wavelength, depending on the first hyperpolarisability of the NLO chromophore. The dipole orientation of all these copolymers is very stable provided the temperature of the films is kept below the temperature threshold of 120 °C, which is below the Tg of the polymers.
Various push-pull azobenzene molecular derivatives showing glassy properties have been processed as thin monomeric amorphous films using spin-coating and thermal evaporation in vacuum. This latter deposition technique yielded homogenous thin films whose surface RMS roughness has been found less than 0.3 Å. Contrarily to spin-coated films requiring external poling for SHG emission, evaporated thin films have proved spontaneously active in second harmonic generation (SHG) when probing at 1.907 μm. Heating above Tg and continuous illumination with an Ar+ laser in the sample absorption maximum band caused dramatic and irreversible disappearance of the spontaneous SHG signal. Applying an external static electric field by using corona discharge induced SHG reversible modulation whose sign has been tuned by changing the bias from positive to negative. Films obtained by vacuum evaporation under a 4 kV voltage underwent considerable morphology changes characterized by the formation of stable 250 nm high nanoclusters evidenced by AFM imaging. The dramatic decrease in SHG has been attributed to the formed nanopillars whose growth depends apparently on the substrate polarization state and must obey a centrosymmetric organization.
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.
Hybrids organic-inorganic nanocomposites are obtained though the hydrolysis and condensation of diethoxymethylsilane and methyltriethoxysilane alkoxides with or without the use of Lewis acids such as Zr(OPrn)4 or Al(etac)(OBus)2 precursors. These materials which present both reductive and hydrophobic behavior are performant host matrices for rare-earth cations and for photochromic dyes such as from spirooxazines (SO), diarylethene derivatives (DE) and furylfulgides (FF). We report the room temperature synthesis of new Eu2+ doped hybrid materials together with their absorption and emission properties. The photochromic properties of the different dyes (SO, DE, FF) in these hybrid solid matrices are also described. Very fast kinetics of coloration and thermal fading (0.2 s-1) are reproducibly evaluated for spiroxazines, while for the first time, quantum yields of the coloration process of diarylethene derivatives and furylfulfydes embedded in solid sol-gel derived matrices are measured.
Several dyes such as a spiropyran, a spirooxazine and two tetraarylporphyrins have been incorporated inside hybrid organic-inorganic matrices synthesized through the acid hydrolysis of dimethyldiethoxysilane and zirconium n- propoxide. These matrices are nanocomposites with well defined hydrophilic (zirconium oxopolymer nodules) and hydrophobic (polydimethylsiloxane chains) domains. As a consequence, they are good candidates to investigate dye-matrix interactions in matrices containing transition metal. These interactions are shown to occur through hydrogen bonds, covalent bonds or Lewis acid-base type bonds. They strongly modify the optical response of the dyes (absorption-emission spectra, lifetime, kinetics...).
Thin films of new side-chain polyimides bearing disperse red one (DR1) groups have been poled by the corona technique assisted by visible irradiation at low temperatures, far below the high glass transition temperature (Tg) of these polymers. The second harmonic generation (SHG) signal reached at the end of this photoassisted poling process is higher than with thermal poling. Furthermore, by a simple method based on absorption measurements with polarized light at variable incidence, it has been shown that the degradation ratio of the chromophores is much lower with photoassisted poling than with thermal poling at a temperature near Tg.
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