104 research outputs found
Huge Electro-/photo-/acidoinduced Second-order Nonlinear Contrasts from Multiaddressable Indolinooxazolodine
In this work, linear and nonlinear optical properties of electro-/acido-/photoswitchable indolino[2,1-b]oxazolidine derivatives were investigated. The linear optical properties of the closed and open forms have been characterized by UV–visible and IR spectroscopies associated with DFT calculations. Nonlinear optical properties of the compounds have been obtained by ex situ and in situ hyper-Rayleigh experiments in solution. We show that protonated, oxidized, and irradiated open forms exhibit the same visible absorption and NLO features. In particular, the closed and open forms exhibit a huge contrast of the first hyperpolarizability with an enhancement factor of 40–45. Additionally, we have designed an original electrochemical cell that allows to monitor in situ the hyper-Rayleigh response upon electrical stimulus. We report notably a partial but good and reversible NLO contrast in situ during oxidation/reduction cycles. Thereby, indolinooxazolidine moieties are versatile trimodal switchable units which are very promising for applications in devices
Photoinduced 3D orientational order in side chain liquid crystalline azopolymers
We apply experimental technique based on the combination of methods dealing
with principal refractive indices and absorption coefficients to study the
photoinduced 3D orientational order in the films of liquid crystalline (LC)
azopolymers. The technique is used to identify 3D orientational configurations
of trans azobenzene chromophores and to characterize the degree of ordering in
terms of order parameters. We study two types of LC azopolymers which form
structures with preferred in-plane and out-of-plane alignment of
azochromophores, correspondingly. Using irradiation with the polarized light of
two different wavelengths we find that the kinetics of photoinduced anisotropy
can be dominated by either photo-reorientation or photoselection mechanisms
depending on the wavelength. We formulate the phenomenological model describing
the kinetics of photoinduced anisotropy in terms of the isomer concentrations
and the order parameter tensor. We present the numerical results for absorption
coefficients that are found to be in good agreement with the experimental data.
The model is also used to interpret the effect of changing the mechanism with
the wavelength of the pumping light.Comment: uses revtex4 28 pages, 10 figure
Effects of Sodium Salts of Lyotropic Anions on Low-Temperature, Ordered Lipid Monolayers
SECOND HARMONIC GENERATION UPON THERMAL POLING AND LIGHT-INDUCED CHIRALITY IN THE AMORPHOUS p(DR1M) AZOBENZENE POLYMER FILMS
Quantitative Determination of the Polar Order Induced under High Electric Field in Amorphous PDR1M Azobenzene Polymer Films
Chromophore Orientations upon Irradiation in Gratings Inscribed on Azo-Dye Polymer Films: A Combined AFM and Confocal Raman Microscopic Study
Effects of silicone coating degradation on GaN MQW LEDs performances using physical and chemical analyses
International audienceThis work presents a physics of failure (POF) methodology coupling failure signatures with physico-chemical analyses. The aim is to work out electro-optical failure signatures located in packaged InGaN/GaN Multiple Quantum Wells Light Emitting Diodes (MQW LEDs). Electrical and optical characteristics performed after accelerated ageing tests (30 mA/85 °C/1500 h), confirm a 65% drop of optical power and an increase of one decade of leakage current spreading at the silicone oil/chip interfaces. Through measurements of silicone coating fluorescence emission spectra, we demonstrate that the polymer enlarges the LED emission spectrum and shifts central wavelength. This shift is related to silicone oil spectral instability and the central wavelength of packaged LED appears to be temperature insensitive. In this paper, we discriminate the degradation of bulk silicone oil responsible for optical losses from the polymer/chip interface inducing larger leakage current
Synthetic Studies toward C-Glucosidic Ellagitannins: A Biomimetic Total Synthesis of 5-O-Desgalloylepipunicacortein A
C-glucosidic ellagitannins constitute a subclass of bioactive polyphenolic natural products with strong antioxidant properties, as well as promising antitumoral and antiviral activities that are related to their capacity to interact with both functional and structural proteins. To date, most synthetic efforts toward ellagitannins have concerned glucopyranosic species. The development of a synthetic strategy to access C-glucosidic ellagitannins, whose characteristic structural feature includes an atropoisomeric hexahydroxydiphenoyl (HHDP) or a nonahydroxyterphenoyl (NHTP) unit that is linked to an open-chain glucose core by a C-aryl glucosidic bond, is described herein. The total synthesis of the biarylic HHDP-containing 5-O-desgalloylepipunicacortein A (1?beta) was achieved by either using the natural ellagic acid bis-lactone as a precursor of the requested HHDP unit or by implementing an atroposelective intramolecular oxidative biarylic coupling to forge this HHDP unit. Both routes converged in the penultimate step of this synthesis to enable a biomimetic formation of the key C-aryl glucosidic bond in the title compound
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