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Barrau S.,CNRS Materials and Transformations Unit of UMET | Vanmansart C.,CNRS Materials and Transformations Unit of UMET | Moreau M.,CNRS Laboratory of Infrared and Raman Spectrochemistry | Addad A.,CNRS Materials and Transformations Unit of UMET | And 3 more authors.
Macromolecules | Year: 2011

The crystallization kinetics and the resulting structure and morphology of polylactide (PLA) were investigated in the presence of carbon nanotubes (CNTs). Nanocomposite samples prepared by solution and melt mixing present homogeneous filler dispersion, as observed by scanning electron microscopy. Calorimetric characterization of the nonisothermal and isothermal crystallization behavior analyzed according to Avrami's theory provides evidence of the significant impact of CNTs on the crystallization kinetics of the PLA matrix. The nucleating effect of the nanofillers is confirmed by Raman spectroscopy experiments. Indeed, during isothermal crystallization, the nanotube characteristic vibrations are strongly affected by the development of polymer crystalline phase. Additionally, CNTs increase the number of nucleation sites and thereby decrease the average spherolite size as observed by optical microscopy. The PLA crystal structure is not modified by the presence of CNTs, as probed by X-ray diffraction. © 2011 American Chemical Society. Source

Deschamps T.,Ecole Polytechnique - Palaiseau | Deschamps T.,Lyon Institute of Nanotechnologies | Vezin H.,CNRS Laboratory of Infrared and Raman Spectrochemistry | Gonnet C.,Draka Comteq France | Ollier N.,Ecole Polytechnique - Palaiseau
Optics Express | Year: 2013

Using a combination of experimental techniques such as optical absorption, Raman scattering, continuous wave and pulse Electron Spin Resonance (ESR), we characterize a set of γ-irradiated Yb3+ doped silica glass preforms with different contents of phosphorous and aluminum. We demonstrate that when P is introduced in excess compared to Al, nearly no radiodarkening is induced by γ-rays. On the other hand, when Al>P, a large absorption band is induced by radiation. Thermal annealing experiments reveal the correlation between the decrease of the optical absorption band and the decrease of the Al-Oxygen Hole Center (AlOHC) ESR signal, demonstrating the main role of AlOHC defects in the fiber darkening. HYSCORE (HYperfine Sublevel CORElation) pulse-ESR experiments show a high Al-P nuclear spin coupling when P>Al and no coupling when Al>P. This result suggests that both AlOHC and POHC creation is inhibited by Al-O-P linkages. Confronting our data with previous works, we show that the well-known photodarkening process, meaning losses induced by the IR pump, can also be explained in this framework. © 2013 Optical Society of America. Source

Barras A.,Lille University of Science and Technology | Boussekey L.,CNRS Laboratory of Infrared and Raman Spectrochemistry | Courtade E.,CNRS Atomic and Molecular Physics Laboratory | Boukherroub R.,Lille University of Science and Technology
Nanoscale | Year: 2013

Hypericin (Hy), a naturally occurring photosensitizer (PS), is extracted from Hypericum perforatum plants, commonly known as St. John's wort. The discovery of the in vitro and in vivo photodynamic activities of hypericin as a photosensitizer generated great interest, mainly to induce a very potent antitumoral effect. However, this compound belongs to the family of naphthodianthrones which are known to be poorly soluble in physiological solutions and produce non-fluorescent aggregates (A. Wirz et al., Pharmazie, 2002, 57, 543; A. Kubin et al., Pharmazie, 2008, 63, 263). These phenomena can reduce its efficiency as a photosensitizer for the clinical application. In the present contribution, we have prepared, characterized, and studied the photochemical properties of Hy-loaded lipid nanocapsule (LNC) formulations. The amount of singlet oxygen (1O2) generated was measured by the use of p-nitroso-dimethylaniline (RNO) as a selective scavenger under visible light irradiation. Our results showed that Hy-loaded LNCs suppressed aggregation of Hy in aqueous media, increased its apparent solubility, and enhanced the production of singlet oxygen in comparison with free drug. Indeed, encapsulation of Hy in LNCs led to an increase of 1O2 quantum yield to 0.29-0.44, as compared to 0.02 reported for free Hy in water. Additionally, we studied the photodynamic activity of Hy-loaded LNCs on human cervical carcinoma (HeLa) and Human Embryonic Kidney (HEK) cells. The cell viability decreased radically to 10-20% at 1 μM, reflecting Hy-loaded LNC25 phototoxicity. © 2013 The Royal Society of Chemistry. Source

Perrier A.,University Paris Diderot | Aloise S.,CNRS Laboratory of Infrared and Raman Spectrochemistry | Olivucci M.,University of Siena | Olivucci M.,Bowling Green State University | And 2 more authors.
Journal of Physical Chemistry Letters | Year: 2013

The understanding of the intimate electronic processes in photochromes is essential to optimize the properties of light-controllable devices. For one of the most studied classes of molecular switches, namely, dithienylethenes, the relative efficiencies of the normal and inverse structures remained puzzling. Indeed, despite a larger ratio of the active antiparallel conformers for the latter, the quantum yields of cyclization of inverse dithienylethenes do not exceed those of its normal counterpart. In the present contribution, we provide the first explanation of this experimental outcome using multireference ab initio quantum chemistry. We demonstrate the existence of a fluorescent intermediate on the S1 state of the inverse system that generates a photochemically unreactive conformation in the ground state. This study paves the way toward a rational development of efficient molecular photochromes presenting a photon-quantitative response. © 2013 American Chemical Society. Source

Mutoh K.,Aoyama Gakuin University | Sliwa M.,CNRS Laboratory of Infrared and Raman Spectrochemistry | Abe J.,Aoyama Gakuin University | Abe J.,Japan Science and Technology Agency
Journal of Physical Chemistry C | Year: 2013

Recently, we have developed a series of fast photochromic imidazole dimers with a [2.2]paracyclophane ([2.2]PC) moiety that bridge diphenylimidazole units and succeeded the acceleration of the thermal decoloration rate. The colorless [2.2]PC-bridged imidazole dimers show a photoinduced homolytic bond cleavage of the C-N bond between the imidazole rings to give a pair of colored imidazolyl radicals upon UV light irradiation, followed by the radical-radical coupling reaction to form the initial C-N bond between the imidazole rings. The decoloration reaction to give the initial imidazole dimer proceeds only thermally. The high quantum yield close to unity of the photochromic reaction and the large extinction coefficient of the radical achieve both high optical density at the photostationary state and rapid switching speed. The application to rapid fluorescence switching has been investigated to develop a new type of photochromic fluorescence switching molecule applicable to super-resolution microscopy. The widespread absorption of the colored radical lying between 500 and 900 nm enables the efficient quenching of the excited electronic state of the fluorophores by Förster resonance energy transfer (FRET) from the fluorophores to the radical moiety. We successfully developed a [2.2]PC-bridged imidazole dimer possessing a fluorescein moiety as a fluorescence unit. This photochromic dye shows fast photochromism to give a pair of imidazolyl radicals that quench the fluorescence from the fluorescent unit by the FRET mechanism. The fluorescence intensity can be switched rapidly with the fast photochromism. © 2013 American Chemical Society. Source

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