Intramolecular Path Determination of Active Electrons on Push-Pull Oligocarbazole Dyes-Sensitized Solar Cells

Several push-pull oligocarbazole dye-sensitizers have been studied using theoretical methods in order to better understand the relationship between structural electronic or optical properties and intramolecular path of active electrons during the ionization and injection processes. DFT/TD-DFT calculations were performed on a series of five dye sensitizers. They differ by the presence of electron donating group (EDG) by inductive effect (noted+I) or electron releasing group (ERG) by mesomeric effect (noted+M) or electron withdrawing group by inductive effect (noted-I) on the pushed part of the dyes studied. Our work focused on the internal distribution of electrons in the different parts of dye that are the push/pull moieties and the π -bridge. The study concerned the ground state, the electronic transition process and the excited state. In each situation, the fragment acting in the ionization or transition phenomena were identified. In the ground state, the electrons of the push part appear to be the least bound because they have the highest probabilities of ionization. In the excited state, the ionized atoms are essentially positioned in the pushing part and some neighboring atoms of the bridge. In the electronic transition, the active atoms are located in the π -conjugated part but only on the side adjacent to the acceptor group. To arrive to this conclusion, we optimized the structures of the five dyes in their ground and excited states. We calculated the atomic charges, the wavelengths and intensities of electronic transitions in the visible domain, the reorganization energies as well as the oxidation potential. It appears that +M donor ligands improve the performance of a dye because the great distribution of atoms to be ionized in the push parts.     

Modèle multi-bulles pour la cavitation

In this study we propose new multi-bubble model for cavitation, in which, to simulate the interactions within a cloud of cavitation at the initial stage, the dynamic behaviour of two nonidentical bubbles localised in a volume of control is studied. The presence of two bubbles introduces an instability in which the exchange of volume seems an additional degree of freedom. Depending on the conditions of expansion, the small bubble can disappear or not. If the small bubble disappears, the volume of control is readjusted to introduce a new small bubble and to continue calculation in a new sequence. The model makes it possible for many small bubbles to disappear as in the appearance of cavitation, which is at the origin of certain phenomena observed in the zone of the appearance, such as emission of the noise. The model reveals especially the pressure rather like a result than a datum.The comparison of the size of the bubbles and the pressure varying in time, obtained with the model are coherent with the measurements taken by Ohl [Phys. Fluids 14 (10) (2002) 3512–3521]. To cite this article: M. Adama Maiga, D. Buisine, C. R. Mecanique 337 (2009).     

Towards the total synthesis of trichormamide A,a cyclic undecapeptide

Lipocyclopeptides isolated from marine sources hold great promise as new lead for therapeutics. Here, we propose the first attempt towards the total synthesis of Trichormamide A. This synthesis will help to confirm the proposed structure of the cyclic lipopeptide.     

Experimental observation of the transition between gas-phase and aqueous solution structures for acetylcholine, nicotine, and muscarine ions

Structural information on acetylcholine and its two agonists, nicotine, and muscarine has been obtained from the interpretation of infrared spectra recorded in the gas-phase or in low pH aqueous solutions. Simulated IR spectra have been obtained using explicit water molecules or a polarization continuum model. The conformational space of the very flexible acetylcholine ions is modified by the presence of the solvent. Distances between its pharmacophoric groups cover a lower range in hydrated species than in isolated species. A clear signature of the shift of protonation site in nicotine ions is provided by the striking change of their infrared spectrum induced by hydration. On the contrary, structures of muscarine ions are only slightly influenced by the presence of water.     

Nickel nanofibers and nanowires: Elaboration by reduction in polyol medium assisted by external magnetic field

Nickel nanowires, with diameter 250 nm and a length of several microns, were prepared by the polyol process (chemical reduction) while an external magnetic field of 1.4 T has been applied during preparation. This combination has allowed the elaboration of Ni nanowires with a yield of over 90%. X-ray diffraction (XRD) showed that these nanowires crystallize with the face-centered-cubic structure. Magnetic static measurements showed the effect on the nanoparticles’ morphology of the external magnetic field applied during the synthesis. They also allowed studying the effect of the external magnetic field on the magnetic properties of nanowires as a function of their orientation. When nanowires are aligned parallel with magnetic field, the hysteresis loop obtained is very open with a coercivity field (Hc) value of 385 Oe and a high remanence to saturation ratio Mr/Ms of 0.85.