École normale supérieure de Cachan

About: École normale supérieure de Cachan is a education organization based out in Cachan, Île-de-France, France. It is known for research contribution in the topics: Decidability & Finite element method. The organization has 2717 authors who have published 5585 publications receiving 175925 citations.

Direct measurement of the photon statistics of a triggered single photon source.

Abstract: We studied intensity fluctuations of a single photon source relying on the pulsed excitation of the fluorescence of a single molecule at room temperature. We directly measured the Mandel parameter Q(T) over 4 orders of magnitude of observation time scale T by recording every photocount. On time scale of a few excitation periods, sub-Poissonian statistics is clearly observed and the probablility of two-photons events is 10 times smaller than Poissonian pulses. On longer times, blinking in the fluorescence, due to the molecular triplet state, produces an excess of noise.

Designing Dye–Nanochannel Antenna Hybrid Materials for Light Harvesting, Transport and Trapping

Abstract: We discuss artificial photonic antenna systems that are built by incorporating chromophores into one-dimensional nanochannel materials and by organizing the latter in specific ways. Zeolite L (ZL) is an excellent host for the supramolecular organization of different kinds of molecules and complexes. The range of possibilities for filling its one-dimensional channels with suitable guests has been shown to be much larger than one might expect. Geometrical constraints imposed by the host structure lead to supramolecular organization of the guests in the channels. The arrangement of dyes inside the ZL channels is what we call the first stage of organization. It allows light harvesting within the volume of a dye-loaded ZL crystal and also the radiationless transport of energy to either the channel ends or center. One-dimensional FRET transport can be realized in these guest-host materials. The second stage of organization is realized by coupling either an external acceptor or donor stopcock fluorophore at the ends of the ZL channels, which can then trap or inject electronic excitation energy. The third stage of organization is obtained by interfacing the material to an external device via a stopcock intermediate. A possibility to achieve higher levels of organization is by controlled assembly of the host into ordered structures and preparation of monodirectional materials. The usually strong light scattering of ZL can be suppressed by refractive-index matching and avoidance of microphase separation in hybrid polymer/dye-ZL materials. The concepts are illustrated and discussed in detail on a bidirectional dye antenna system. Experimental results of two materials with a donor-to-acceptor ratio of 33:1 and 52:1, respectively, and a three-dye system illustrate the validity and challenges of this approach for synthesizing dye-nanochannel hybrid materials for light harvesting, transport, and trapping.

Hybrid Molecular-Based Magnets Containing Organic NLO Chromophores: A Search toward an Interplay between Magnetic and NLO Behavior

Abstract: A new hybrid molecular-based ferromagnet of formula [(dmaph)PPh3][MnCr(ox)3], where [(dmaph)PPh3]+ stands for the (4-dimethylaminophenyl)triphenylphosphonium cation (ox2- being the oxalate anion), has been synthesized. It crystallizes in the monoclinic P21 space group, with lattice parameters a = 13.954(2) A, b = 16.297(2) A, c = 14.323(2) A, and β = 99.27(1)°. Refinement based on Fo2 yields R = 0.072 and wR2 = 0.156. The compound exhibits a ferromagnetic interaction between Cr3+ and Mn2+, with a long-range magnetic ordering at TC = 4.5 K. The hyperpolarizability (β) of the cation is calculated within the framework of the INDO/SOS-based method, which indicates a β value comparable to that of p-nitroaniline for an absorption maximum at 306 nm (emax = 28 500 M-1 cm-1). This result is consistent with the observation of a SHG efficiency 4 times that of urea for the parent [(dmaph)PPh3]Br salt, at 1.907 μm. The non-centrosymmetric [(dmaph)PPh3][MnIICrIII(ox)3] derivative is used as a model compound for an inve...