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A venir ...

 
Jeudi 14 Décembre 2017
Emilie Franceschini
Laboratoire de Mécanique et d’Acoustique LMA CNRS UPR 7051
Ultrasonics reveal red blood cell aggregation and cell death index
Quantitative UltraSound (QUS) techniques for estimating cellular structures are based on frequency analysis of signals backscattered from biological tissues. Our QUS method is model-based: the backscatter coefficient (obtained from the power spectrum of the backscattered signals) is estimated from experiments and is fit to a theoretical scattering model. The fit parameters can provide a meaningful description of the tissue microstructure (i.e., scatterer size, shape, scattering strength and spatial organization). During this seminar, I will focus on two questions in the field of QUS: 1) How the high cellular number density and cell clustering in blood affect ultrasound backscattering? 2) What causes an increase of ultrasound backscatter during the cell death process?

Lundi 8 Janvier 2018
Anthony D'ALEO
CINaM UMR 7325, Campus de Luminy - Department of Physics, QMMRC, Ewha Womans University, Seoul 120-750, South Korea
Curcuminoid borondifluoride for preparation of efficient TADF near infrared OLEDs and organic solid-state lasers
Thermally-activated delayed fluorescent (TADF) emitters have been successfully used in organic light-emitting diodes (OLEDs) with up to 100% internal quantum efficiencies and are now considered as the third generation of OLED materials.1 However, the developed dyes, to date, are pretty much limited to visible wavelength (going from sky blue to the red part of the spectrum). In this context, it remains challenging to obtain Near InfraRed (NIR) dyes2 with high photoluminescence quantum yields and electroluminescence external quantum efficiency (EQE). In this context, I will report on the fabrication of NIR TADF OLEDs with a maximum EQE of nearly 10%. The devices used a solution-processable heavy-metal-free donor-acceptor-donor borondifluoride curcuminoid derivative3,4,5 as NIR emitter. Photophysical study and density function theory were used to characterize the dye. This compound shows large ground state and excited state dipole moments. Furthermore, a rather high photoluminescence quantum yield (up to 69%) in solid matrices with an emission maximum wavelength typically in the range between 720 and 750 nm was obtained. Time-resolved photophysical measurements show that the TADF mechanism of this NIR emitter is due to a reverse intersystem crossing from triplet charge transfer (CT) to singlet CT excited states. In addition, the TADF emission wavelength and efficiency are found to strongly depend on the dye concentration in the emissive layer due to the large dipole moments of this compound. In the last part of this talk, I will demonstrate that this new TADF materials exhibits amplified spontaneous emission in the NIR region, suggesting the possibility to harvest triplet excitons for stimulated emission. References [1] H. Uoyama, K. Goushi, K. Shizu, H. Nomura and C. Adachi, “Highly efficient organic light-emitting diodes from delayed fluorescence” Nature 492, pp.234-238, 2012. [2] ]: A. D'Aléo, M. H. Sazzad, D.-H. Kim, EY. Choi, J. W. Wu, G. Canard, F. Fages, J.-C. Ribierre and C. Adachi “Boron difluoride hemicurcuminoid as an efficient far red to near-infrared emitter: toward OLEDs and laser dyes” Chem. Commun. Vol53, pp.7003-7006, 2017. [3] A. Felouat, A. D'Aléo, F. Fages, “Synthesis and Photophysical Properties of Difluoroboron Complexes of Curcuminoid Derivatives Bearing Different Terminal Aromatic Units and a meso-Aryl Ring” J. Org. Chem. Vol78, pp.4446-4455, 2013 [4] K. Kamada, T. Namikawa, S. Senatore, C. Matthews, P.-F. Lenne, O. Maury, C. Andraud, M. Ponce-Vargas, B. Le Guennic, D. Jacquemin, P. Agbo, D. D. An, S. S. Gauny, X. Liu, R. J. Abergel, F. Fages, A. D’Aléo “Two-photon absorption and brightness optimization of curcuminoid borondifluoride complexes” Chem. Eur. J. Vol22, pp.5219–5232, 2016. [5] G. Canard, M. Ponce-Vargas, D. Jacquemin, B. Le Guennic, A. Felouat, M. Rivoal, E. Zaborova, A. D'Aléo and F. Fages “Influence of the electron donor groups on the optical and electrochemical properties of borondifluoride complexes of curcuminoid derivatives: a joint theoretical and experimental study” RSC Adv. Vol7, 10132-10142, 2017.

Jeudi 18 Janvier 2018
Matthias HILLENKAMP
Institut Lumière Matière, UMR5306 CNRS, Université Claude Bernard Lyon 1, France and Instituto de Física
Size effects in physically prepared metal nanoparticles
In this presentation I will discuss experimental methods for the fabrication of mono- and bi-metallic clusters and nanoparticles in the gas phase by physical means. When embedded in stable solid matrices, they form cluster-assembled nanostructures with variable and size-dependent properties. In particular I will address the following topics as examples: Fabrication of cluster-assembled nanostructures: magnetron sputtering/aggregation versus laser vaporization. Size effects in the magnetic anisotropy of embedded cobalt nanoparticles: from surface to shape. Size effects in the electronic and vibrational relaxation in small silver clusters as evidenced by ultrafast femtosecond spectroscopy: the departure from the scalable size regime. Study of size effects in the electronic structure of size-selected very small silver clusters: optical spectroscopy vs. Electron Energy Loss Spectroscopy. Structural, optical and magnetic properties of bi-metallic FeAg nanoparticles: optical spectroscopy, magnetometry and synchrotron-based XMCD and EXAFS.