Huge Electro-/photo-/acidoinduced Second-order Nonlinear Contrasts from Multiaddressable Indolinooxazolodine

In this work, linear and nonlinear optical properties of electro-/acido-/photoswitchable indolino[2,1-b]oxazolidine derivatives were investigated. The linear optical properties of the closed and open forms have been characterized by UV–visible and IR spectroscopies associated with DFT calculations. Nonlinear optical properties of the compounds have been obtained by ex situ and in situ hyper-Rayleigh experiments in solution. We show that protonated, oxidized, and irradiated open forms exhibit the same visible absorption and NLO features. In particular, the closed and open forms exhibit a huge contrast of the first hyperpolarizability with an enhancement factor of 40–45. Additionally, we have designed an original electrochemical cell that allows to monitor in situ the hyper-Rayleigh response upon electrical stimulus. We report notably a partial but good and reversible NLO contrast in situ during oxidation/reduction cycles. Thereby, indolinooxazolidine moieties are versatile trimodal switchable units which are very promising for applications in devices

Methyl group reorientation in molecular crystals : present knowledge and prospective

The physical methods which are more usually used to study the internal reorientation of the methyl group in the solid state are briefly described. A short review of the present knowledge and of the future prospects are presented in the case of some molecular crystals and more especially for toluene and nitromethane

Étude théorique du potentiel de rotation du groupe méthyle dans un cristal de nitrométhane à 4°K

Une étude théorique de la rotation du groupement méthyle d’une molécule de nitrométhane en Interaction avec les trente plus proches voisines a été effectuée afin de retrouver et d’interpréter le potentiel expérimental. Après avoir analysé l’origine du potentiel, l’étude a été poursuivie afin de déterminer le rôle de chaque type d’atomes ainsi que la contribution des différentes molécules au potentiel

Effect of the internal rotation of the CHD2 group on the CH stretching mode of nitromethane NO2CHD2 in crystalline phase

The infrared and Raman spectra of nitromethane NO2CHD2 in crystalline state have been recorded in the CH stretching mode range in a large temperature range (17 to 185 K). At very low temperatures, three bands are observed; each of them is assigned to the vibration of a CH oscillator localized in a different site. A quantum theory of these spectra shows that no tunnelling effect appears; this is in agreement with the classical interpretation. Furthermore, this theory ascribes the temperature dependence of the relative intensities of the v(CH) bands to the population density of the first torsional levels in the vibrational ground state and suggests a very simple ordering of the isotopic system CHD2 at 4 K, the CH vibrator being localized in the plane perpendicular to the molecular plane. At higher temperatures, the strong relaxation observed on these v(CH) bands is due to the CHD2 group reorientation and can be described, mostly, by a great amplitude random jump process.Les spectres infrarouges et Raman du nitrométhane NO2CHD 2 cristallisé ont été enregistrés dans la région de la vibration de valence CH dans un grand domaine de températures (17 à 185 K). A très basse température, les spectres présentent trois bandes; chacune d'elles est attribuée à la vibration d'un oscillateur CH localisé dans un site différent. Une théorie quantique de ces spectres montre qu'aucun effet tunnel n'apparaît, ce qui est en accord avec l'interprétation classique. De plus, cette théorie permet de relier la variation des intensités relatives des bandes v(CH) en fonction de la température à la densité de population des premiers niveaux de torsion dans l'état fondamental de vibration et suggère une mise en ordre très simple du système isotopique CHD2 à 4 K, le vibrateur CH étant localisé dans le plan perpendiculaire au plan de la molécule. A plus haute température, la forte relaxation observée sur ces bandes v(CH) est due à la réorientation du groupe CHD2 et peut être décrite, pour sa plus grande partie, par un processus de sauts aléatoires de grande amplitude

Ab-Initio calculations of proline vibrations with and without water, consequences on the infrared spectra of proline-rich proteins

The infrared spectra of proline rich proteins display a strong band in the 1450 cm-1 region. In the literature, this band was assigned either to the deformation modes of the CH2 and CH3 groups or to the CN stretching mode of proline residues. In order to establish the correct assignment of this band, the impact of proline vibrations in a polypeptide chain is studied and ab-initio calculations are performed for a model molecule (I) containing a repeat unit of polyproline. A strong band is effectively calculated in the 1450 cm-1 region and mostly assigned to CN stretching whereas, due to the absence of N-H bond, there is no amide II band. These results are in good agreement with the spectral features observed in the FTIR spectra of gliadins. Moreover, the spectral shifts calculated when a water molecule is complexed with (I) are consistent with the hydration effect observed in the experimental data

Ab-Initio calculations of proline vibrations with and without water, consequences on the infrared spectra of proline-rich proteins

International audienceThe infrared spectra of proline rich proteins display a strong band in the 1450 cm-1 region. In the literature, this band was assigned either to the deformation modes of the CH2 and CH3 groups or to the CN stretching mode of proline residues. In order to establish the correct assignment of this band, the impact of proline vibrations in a polypeptide chain is studied and ab-initio calculations are performed for a model molecule (I) containing a repeat unit of polyproline. A strong band is effectively calculated in the 1450 cm-1 region and mostly assigned to CN stretching whereas, due to the absence of N-H bond, there is no amide II band. These results are in good agreement with the spectral features observed in the FTIR spectra of gliadins. Moreover, the spectral shifts calculated when a water molecule is complexed with (I) are consistent with the hydration effect observed in the experimental data