Driss Rayane

Bio: Driss Rayane is an academic researcher from University of Lyon. The author has contributed to research in topics: Dipole & Polarizability. The author has an hindex of 28, co-authored 75 publications receiving 2045 citations. Previous affiliations of Driss Rayane include University of Montpellier & Claude Bernard University Lyon 1.

Direct measurement of the electric polarizability of isolated C60 molecules

Abstract: We present the first direct measurement of the electric polarizability of isolated C60 molecules by molecular beam deflection technique. We have obtained a value of 76.5±8.0 A3 which is consistent with most of the recent calculations and slightly lower than the value of the polarizability of C60 measured in fullerite crystals.

Non-linear optical properties of gold quantum clusters. The smaller the better.

Abstract: By developing a new method for synthesizing atomically monodisperse Au15 nanoclusters stabilized with glutathione molecules and using the current state-of-the-art methods for synthesizing monodisperse protected Au25 nanoclusters, we investigated their nonlinear optical (NLO) properties after two-photon absorption. The two-photon emission spectra and the first hyperpolarizabilities of these particles were obtained using, in particular, a hyper-Rayleigh scattering technique. The influence on NLO of the excitation wavelength, the size as well as the nature of the ligands is also explored and discussed. Au15, the smallest stable thiolated gold nanocluster, presents remarkable nonlinear properties with respect to two-photon processes. The two-photon absorption cross-section at 780 nm for Au15 is ∼65 700 GM. This experimental cross-section value points to a quantum yield for two-photon emission of about 3 × 10−7 at 475 nm for Au15. The first hyperpolarizability β for Au15 clusters (509 × 10−30 esu), as compared to Au25 clusters (128 × 10−30 esu), is larger considering the difference in the number of gold atoms. Also, 1030 β per atom values reported for Au15 and Au25 clusters are more than two orders of magnitude larger than the values reported for Au NPs in the size range 10–50 nm, outlining the quantum cluster regime.

Synthesis, characterization and optical properties of low nuclearity liganded silver clusters: Ag31(SG)19 and Ag15(SG)11.

Abstract: We report a simple synthesis of silver:glutathione (Ag:SG) clusters using a cyclic reduction under oxidative conditions. Two syntheses are described which lead to solutions containing well-defined Ag31(SG)19 and Ag15(SG)11 clusters that have been characterized by mass spectrometry. The optical properties of silver:glutathione (Ag:SG) cluster solutions have been investigated experimentally. In particular, the solution containing Ag15(SG)11 clusters shows a bright and photostable emission. For Ag31(SG)19 and Ag15(SG)11 clusters, the comparison of experimental findings with DFT and TDDFT calculations allowed us to reveal the structural and electronic properties of such low nuclearity liganded silver clusters.

Permanent electric dipole and conformation of unsolvated tryptophan.

Abstract: We have coupled a matrix assisted laser desorption source to an electric beam deflection setup to measure the permanent electric dipole of tryptophan isolated in a molecular beam. The permanent electric dipole is sensitive to the geometry and can be used as a tool to probe the conformation. For tryptophan, the dominant conformation present in the molecular beam has a dipole moment that agrees with the lowest energy conformation found at the B3LYP-DFT/6-31G* and MP2/6-31G* levels of theory. This conformation is stabilized by (COOHNH2) hydrogen bonding and through a favorable interaction between the NH2 group and the indole ring. Other low-energy conformations found in the calculations have dipole moments that are either too small or too large to account for the experimental results. In recent years there has been considerable interest in obtaining structural information for unsolvated and partially solvated biomolecules.1 These studies can provide detailed information about intramolecular interactions and solvent interactions that determine the conformations in all environments. In particular, a variety of sophisticated spectroscopic methods have been employed to examine isolated amino acids such as glycine,2,3 alanine,4 arginine,5 phenylalanine,6 tryptophan7-9 and tyrosine.8,10 The first spectroscopic results for tryptophan isolated in a molecular beam were obtained in 1985 by Levy and collaborators.7 They identified six different conformations in the resonantly enhanced two-photon ionization spectrum of jet-cooled tryptophan. More recently, high-resolution vibronic spectra were recorded for tryptophan at 0.38 K in helium droplets.8 However, the equilibrium structure has still not been determined. In the work described here we have used electric deflection of a molecular beam to directly probe the permanent dipole of tryptophan. Until very recently,11 this approach has mainly been restricted to the study of alkali halide dimers.12 This is the first application of the electric deflection method to a biomolecule. The experimental apparatus consists of a matrix assisted laser desorption (MALD) source coupled to an electric beam deflection setup that incorporates a position-sensitive time-of-flight mass spectrometer. Tryptophan and nicotinic acid were mixed in a 1:10 molar ratio and pressed to form a rod. A pulsed molecular beam of tryptophan was produced by desorbing molecules from the rod with the third harmonic of a Nd:YAG laser into a helium carrier gas. At the exit of the source, the tryptophan molecules are thermalized to 85 K in a 50 mm long nozzle cooled by liquid nitrogen. The molecular beam is collimated by two slits, and then goes through an electric deflector with a “two-wire” electric field configuration.13 One meter after the deflector, the molecules are ionized with the fourth harmonic of a Nd:YAG laser (266 nm) in the extraction region of a position-sensitive time-of-flight mass spectrometer.13 The tryptophan is two-photon ionized. The wavelength used for ionization (266 nm) is close to the resonance band of the indole moeity in tryptophan. There is relatively little fragmentation, roughly 80% of the ion signal is observed at the parent mass channel. Measurements of the molecular beam profile were performed as a function of the electric field in the deflector. The beam velocity was determined with a chopper. Figure 1 shows examples of the molecular beam profiles obtained without and with an electric field of 6.7 × 106 V/m in the deflector. The profiles were averaged over 10 000 laser shots. A symmetrical broadening of the profile and a decrease in the intensity on the beam axis are observed when the field is turned on. Similar profiles with a regular increase in the broadening are observed as the electric field is increased from 0 to 1.5 × 107 V/m. The force in the deflector is due to the interaction between the electric field Fz and the dipole μ of the molecule. It can be written as:14

Atomically Precise Colloidal Metal Nanoclusters and Nanoparticles: Fundamentals and Opportunities

Abstract: Colloidal nanoparticles are being intensely pursued in current nanoscience research. Nanochemists are often frustrated by the well-known fact that no two nanoparticles are the same, which precludes the deep understanding of many fundamental properties of colloidal nanoparticles in which the total structures (core plus surface) must be known. Therefore, controlling nanoparticles with atomic precision and solving their total structures have long been major dreams for nanochemists. Recently, these goals are partially fulfilled in the case of gold nanoparticles, at least in the ultrasmall size regime (1–3 nm in diameter, often called nanoclusters). This review summarizes the major progress in the field, including the principles that permit atomically precise synthesis, new types of atomic structures, and unique physical and chemical properties of atomically precise nanoparticles, as well as exciting opportunities for nanochemists to understand very fundamental science of colloidal nanoparticles (such as the s...

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Abstract: : The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Atomically Precise Clusters of Noble Metals: Emerging Link between Atoms and Nanoparticles

Abstract: Atomically precise pieces of matter of nanometer dimensions composed of noble metals are new categories of materials with many unusual properties. Over 100 molecules of this kind with formulas such as Au25(SR)18, Au38(SR)24, and Au102(SR)44 as well as Ag25(SR)18, Ag29(S2R)12, and Ag44(SR)30 (often with a few counterions to compensate charges) are known now. They can be made reproducibly with robust synthetic protocols, resulting in colored solutions, yielding powders or diffractable crystals. They are distinctly different from nanoparticles in their spectroscopic properties such as optical absorption and emission, showing well-defined features, just like molecules. They show isotopically resolved molecular ion peaks in mass spectra and provide diverse information when examined through multiple instrumental methods. Most important of these properties is luminescence, often in the visible–near-infrared window, useful in biological applications. Luminescence in the visible region, especially by clusters prot...

Property-optimized gaussian basis sets for molecular response calculations.

Abstract: With recent advances in electronic structure methods, first-principles calculations of electronic response properties, such as linear and nonlinear polarizabilities, have become possible for molecules with more than 100 atoms. Basis set incompleteness is typically the main source of error in such calculations since traditional diffuse augmented basis sets are too costly to use or suffer from near linear dependence. To address this problem, we construct the first comprehensive set of property-optimized augmented basis sets for elements H–Rn except lanthanides. The new basis sets build on the Karlsruhe segmented contracted basis sets of split-valence to quadruple-zeta valence quality and add a small number of moderately diffuse basis functions. The exponents are determined variationally by maximization of atomic Hartree–Fock polarizabilities using analytical derivative methods. The performance of the resulting basis sets is assessed using a set of 313 molecular static Hartree–Fock polarizabilities. The mean...

Atomically precise metal nanoclusters: stable sizes and optical properties

Abstract: Controlling nanoparticles with atomic precision has long been a major dream of nanochemists. Breakthroughs have been made in the case of gold nanoparticles, at least for nanoparticles smaller than ∼3 nm in diameter. Such ultrasmall gold nanoparticles indeed exhibit fundamentally different properties from those of the plasmonic counterparts owing to the quantum size effects as well as the extremely high surface-to-volume ratio. These unique nanoparticles are often called nanoclusters to distinguish them from conventional plasmonic nanoparticles. Intense work carried out in the last few years has generated a library of stable sizes (or stable stoichiometries) of atomically precise gold nanoclusters, which are opening up new exciting opportunities for both fundamental research and technological applications. In this review, we have summarized the recent progress in the research of thiolate (SR)-protected gold nanoclusters with a focus on the reported stable sizes and their optical absorption spectra. The crystallization of nanoclusters still remains challenging; nevertheless, a few more structures have been achieved since the earlier successes in Au102(SR)44, Au25(SR)18 and Au38(SR)24 nanoclusters, and the newly reported structures include Au20(SR)16, Au24(SR)20, Au28(SR)20, Au30S(SR)18, and Au36(SR)24. Phosphine-protected gold and thiolate-protected silver nanoclusters are also briefly discussed in this review. The reported gold nanocluster sizes serve as the basis for investigating their size dependent properties as well as the development of applications in catalysis, sensing, biological labelling, optics, etc. Future efforts will continue to address what stable sizes are existent, and more importantly, what factors determine their stability. Structural determination and theoretical simulations will help to gain deep insight into the structure–property relationships.