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

Molecular dynamics in liquid cyclopropane. III. Depolarized Rayleigh scattering

Depolarized Rayleigh scattering profiles of pure liquid cyclopropanes H 6 and D6 were recorded in the temperature range 155-298 K and at room temperature for dilution at different concentrations in carbon tetrachloride. The analysis of these profiles shows that they cannot be interpreted by assuming only orientational fluctuations of the molecules. The symmetrized spectral densities Î(v) and v 2.Î(v) are well reproduced if one assumes that they result from a weighted sum of two components. The former, nearly Lorentzian, whose width at room temperature and different dilutions in carbon tetrachloride, is close to the rotational Raman one indicates the effect of molecular reorientations. At lower temperature this component becomes wider than the rotational Raman profile, which indicates an organization of the liquid in which the molecules tend to be oriented orthogonally to one other. The second component, much wider, is a damped oscillator profile. The characteristic relaxation time of this oscillator, which is shorter than the orientational correlation time, could be that of a fast variable governing the temporal evolution of the induced polarizabilities. The effect of the temperature on this relaxation time is discussed within the framework of the theories of induced spectra. The intensity of this component, which represents the major part of the spectrum, is of the order of magnitude normally expected for a spectrum produced by a dipole-induced dipole mechanism. It decreases with temperature, probably as a result of an effect of symmetrization of the molecular environment. Nevertheless, the eventual coupling of the orientational slow variable with the fast variable can have an influence on the ratio of the intensities of both components. Finally, the values of the correlation time and of the second and fourth moments associated with the fast variable are weakly temperature dependent and are such that the profile associated with this variable presents an exponential shape in a large frequency range.Les profils Rayleigh dépolarisés du cyclopropane H6 et D 6 ont été enregistrés à l'état liquide pur dans la gamme de températures 155-298 K et à température ambiante en solution à différentes concentrations dans le tétrachlorure de carbone. L'analyse des profils obtenus montre qu'ils ne peuvent pas être interprétés en prenant en compte seulement les fluctuations orientationnelles des molécules. Les densités spectrales symétrisées Î(V) et v2.Î(v) sont bien reproduites en supposant qu'elles résultent d'une somme pondérée de deux composantes. La première, sensiblement Lorentzienne dont la largeur à température ordinaire et aux différentes dilutions dans le tétrachlorure de carbone est voisine de la largeur rotationnelle Raman, traduit l'effet des réorientations moléculaires. Cette composante devient à plus basse température plus large que le profil rotationnel Raman, ce qui indique une organisation du liquide où les molécules tendent à s'orienter mutuellement de manière orthogonale. La deuxième composante, beaucoup plus large, est un profil d'oscillateur amorti. Le temps de relaxation caractéristique de cet oscillateur beaucoup plus court que le temps de corrélation orientationnel, pourrait être celui d'une variable rapide commandant l'évolution temporelle des polarisabilités induites. L'influence de la température sur ce temps de relaxation est discutée à la lumière des théories des spectres induits. L'intensité de cette composante qui représente la majeure partie du spectre est de l'ordre de grandeur attendu dans l'hypothèse d'un spectre induit par mécanisme dipôle-dipôle induit. Elle diminue avec la température par suite probablement d'un effet de symétrisation de l'environnement moléculaire. Toutefois, le couplage éventuel de la variable lente orientationnelle et de la variable rapide peut influer sur le rapport d'intensité des deux composantes. Enfin, les valeurs du temps de corrélation et des moments d'ordre deux et quatre associés à la variable rapide dépendent peu de la température et sont telles que le profil associé à cette variable a une allure exponentielle dans un large domaine de fréquence

Revisited vibrational assignments of imidazolium-based ionic liquids

Imidazolium-based ionic liquids (ILs) involving anions of variable coordinating strength have been investigated using infrared (IR) and Raman spectroscopies, density functional theory (DFT) calculations and selective deuteration of the imidazolium CH groups. Particular emphasis has been placed on the vibrational assignments of the anion and cation internal vibrations, a prerequisite before any interpretation of spectral changes due to ion-ion interactions in these unconventional liquids. The vibrations of highly symmetric and weakly coordinating anions, such as PF(6)(-), have unperturbed wavenumbers, but unexpected IR or Raman activity for some modes, showing that the anion is subjected to an anisotropic electric field. The stretching as well as the in-plane and out-of-plane bending modes of the imidazolium CH groups are anharmonic. They give broad bands that reflect a large distribution of interactions with the surrounding anions. All the bending modes are mixed with ring vibrations and the stretching modes are complicated by Fermi resonance interactions with overtones and combination of in-plane ring modes. However, the stretching vibration of the quasi-diatomic C((2))-D bond appears to be a good spectroscopic probe of the increasing cation-anion interactions when the coordinating strength of the anion increases. The broad absorption observed in the far IR with weakly coordinating anions remains practically unchanged when the acidic C((2))-H imidazolium bond is methylated and even when the imidazolium cation is substituted by tetra-alkyl ammonium or pyrrolidinium cations. It is concluded that this absorption is a general feature of any IL, coming from the relative translational and librational motions of the ions without needing to invoke C((2))-H anion hydrogen bonds