Etude théorique de la molécule d'anthracène par la spectroscopie Infrarouge

Dans ce travail, la géométrie optimisée, les fréquences des vibrations, les intensités infrarouges et les degrés de liberté de la molécule organique d'anthracène sont déterminés dans son état fondamental à l'aide de la fonctionnelle B3LYP (Becke à trois paramètres de Lee-Yang-Parr) avec la base 6-31+G*. Les résultats calculés sont en meilleure concordance avec les données expérimentales

Détermination des déplacements chimiques de RMN (1H) pour quelques molécules organiques

Dans ce travail, nous avons étudié quelques hydrocarbures aromatiques polycycliques (PAHs) en phase gazeuse par la spectroscopie de Résonance Magnétique Nucléaire (RMN 1H) en utilisant la méthode des Orbitales Atomiques Invariantes de Jauge (GIAO). Nous avons déterminé les paramètres magnétiques nucléaires de RMN (constantes d'écran et déplacements chimiques) pour les trois molécules organiques : benzène, naphtalène et anthracène. Ces paramètres d'investigation constituent des sondes théoriques très sensibles pour les structures électroniques et géométriques pour un composé

Investigation théorique ab-initio des molécules organiques

Dans ce article, nous avons fait l'étude théorique de deux molécules organiques (benzène et naphtalène) par la spectroscopie d'Infrarouge via la fonctionnelle B3LYP (Becke à trois paramètres de Lee-Yang-Parr) avec la base 6-31+G* dans leurs états stables. Nous avons calculé les fréquences des vibrations et déterminé les modes de vibration pour ces systèmes.

Role of surface defects in colloidal cadmium selenide (CdSe) nanocrystals in the specificity of fluorescence quenching by metal cations

International audienceThis study aimed to answer the question as whether crystal defects at the surface of soluble capped CdSe nanocrystals (or quantum dots, QDs) in water colloidal suspension are involved in the mechanism of fluorescence quenching induced by metal cations. Nanocrystals of CdSe were synthesized by an aqueous protocol, varying the ratio between the CdSe precursors and the grafted ligand mercaptosuccinic acid (MSA). Changing the MSA/CdSe ratio during synthesis impacts the crystal nucleation growth, which plays an important role in surface construction of CdSe QDs and changes the surface state. In this way, we could modulate the crystal surface defects of CdSe, as verified by analysis of the individual bands which constitute the emission spectra and are associated with different relaxation processes. We found that the various tested metal cations, which interact in solution with the MSA ligand grafted on the QDs, quench their fluorescence differently, depending on the MSA/CdSe ratio used in synthesis. The crystal defects modulate the excitonic relaxation in CdSe and we demonstrated here that the surface defects intervene in the quenching of QDs induced by the binding of cations

Raman Tweezers Microspectroscopy of Functionalized 4.2 nm Diameter CdSe Nanocrystals in Water Reveals Changed Ligand Vibrational Modes by a Metal Cation

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Raman Tweezers Microspectroscopy of Functionalized 4.2 nm Diameter CdSe Nanocrystals in Water Reveals Changed Ligand Vibrational Modes by a Metal Cation

International audienceWe demonstrated the possibility of acquiring Raman spectra of colloidal quantum dots (QDs) at low concentration in water with a size as small as 2.5 nm in diameter using Raman tweezers microspectroscopy. We measured the spectra of CdSe QDs capped with thioglycerol and with L-cysteine. This technique was applied to probe the interaction between Co 2+ and Cys-CdSe QDs whose fluorescence emission is quenched in the presence of this metal cation. The quenching mechanism was so far hypothetical. The Raman spectra of Cys-CdSe QDs recorded in the absence and in the presence of Co 2+ demonstrated the binding of Co 2+ cations to the carboxylate groups of the L-cysteine ligand grafted on the surface of the 4.2 nm CdSe QDs. The frequency of modes for the grafted ligand is changed with respect to the free ligand in solution. Considering the vibrational coupling between the excitonic state and the ligand, we inferred that the binding of a metal cation to the grafted ligand modifies this coupling, so that exciton relaxation through crystal defects is favored. This result rationalizes the fluorescence quenching observed during the metal cation-QD interaction

A Context-Based Approach for Real-Time Adaptation Need Detection

International audienceThe increasingly dynamic and changing environment in which business processes are evolving requires companies to adapt them frequently. Thus, we propose in this paper a new context-based approach recommending to analyze well the environmental changes. This approach recommends to structure knowledge required for process adaptation need in accordance with our BPMN4V-Context meta-model, which supports the modeling of the operating environment, using the context along with the versions of the model of each BPMN process and their use conditions. It also advocates (i) a filtering activity to retain only significant context changes in the monitored data, as low-level context parameters, (ii) a reasoning activity to deduce high-level context parameters from filtered low-level ones, enhancing the current situation of running processes and (iii) examining the current situation before its analysis in order to resolve problems related to the used units and synonym values. Finally, the feasibilit y and applicability of this approach is demonstrated by a case study from the crisis domain and two performance tests

Tailoring the photophysical properties and excitonic radiative decay of soluble CdSe quantum dots by controlling the ratio of capping thiol ligand

International audienceWe report the physical and photophysical properties of CdSe quantum dots capped with three different thiol compounds (thioglycolic acid, 3-mercaptopropionic acid, mercaptosuccinic acid) synthesized through a hydrothermal protocol. We calculated the true molecular weight and molar absorption coefficient of QDs from their diameter (not from any empirical relation) which are in the range 3.5 – 5.9 nm. The aqueous synthesis method ensures the insertion of the sulfur atoms of thiol ligands in the crystal CdSe cubic lattice, producing hexagonal crystal unit defects at the surface of the QDs. The QDs steady-state emission spectra were analyzed in terms of Gaussian components, in correlation with the time-resolved emission. We have elaborated MSA-CdSe QDs capped with mercaptosuccinic acid using various stoichiometric Cd/MSA ratios during the aqueous synthesis. Modulating the Cd/MSA ratio directly affects the size and photophysics of the QDs, in particular the fluorescence emission spectrum and decay. We rationalized the effect on QDs size by a change of the CdSe formation rate during synthesis. Acting on the Cd/MSA ratio appears a mean of modulating the emission spectrum and understanding the photophysical processes involved with respect to the QD structure

A context-based approach for modelling and querying versions of BPMN processes

International audienceVersioning is an interesting solution to deal with business process flexibility. It consists of the definition of several process versions for taking into account the significant changes occurring to the processes. It allows the running of several instances of the same process according to different models. However, in a multi-version environment, where numerous versions co-exist, it is important to specify the context in which these versions can be used. The context is used in particular to find out, for a given situation, the appropriate process version to be executed at run-time. We aim in this paper at offering a solution to model the context of versions of intra- and inter-organisational processes and query these versions using their context. More precisely the recommended solution extends BPMN2.0, the de-facto standard for process modelling, to consider versions and contexts, and introduces a context based language for versions querying

Synthesis, characterization and spectral temperature-dependence of thioglycerol-CdSe nanocrystals

International audienceWater-soluble CdSe quantum dots (QDs) have been synthesized with thioglycerol as a stabilizer through a novel hydrothermal route. The obtained thioglycerol capped CdSe (TG-CdSe) nanocrystals were characterized regarding their morphology and structural, thermal and optical properties. The resulting nanocrystals were synthesized in the cubic structure with a near spherical shape, as confirmed by X-ray diffraction and transmission electron microscopy. Combining transmission electron microscopy imaging and calculations using UV–visible absorption spectrum and X-ray diffraction pattern, the diameter of the synthesized nanocrystals was estimated to 2.26 nm. As confirmed by its Fourier transform IR spectrum, thioglycerol was successfully liganded on the surface of the resulting nanocrystals. Band structure parameters of the TG-CdSe nanoparticles were determined and quantum confinement effect was evidenced by optical absorption, fluorescence and Raman measurements. The thermal properties of the TG-CdSe were explored by thermal gravimetric analysis and differential scanning calorimetry. The temperature dependence of both the absorption and fluorescence spectra in the physiological range makes the TG-CdSe nanocrystals sensitive temperature markers, a property that must be taken into account when developing any probing applications, especially for cellular imaging