Pierre-Marie Gassin

Surface Activity and Molecular Organization of Metallacarboranes at the Air–Water Interface Revealed by Nonlinear Optics

Because of their amphiphilic structure, surfactants adsorb at the water-air interface with their hydrophobic tails pointing out of the water and their polar heads plunging into the liquid phase. Unlike classical surfactants, metallabisdicarbollides (MCs) do not have a well-defined amphiphilic structure. They are nanometer-sized inorganic anions with an ellipsoidal shape composed of two carborane semicages sandwiching a metal ion. However, MCs have been shown to share many properties with surfactants, such as self-assembly in water (formation of micelles and vesicles), formation of lamellar lyotropic phases, and surface activity. By combining second harmonic generation and surface tension measurement, we show here that cobaltabis(dicarbollide) anion {[(C2B9H11)2Co](-) also named [COSAN](-)} with H(+) as a counterion, the most representative metallacarborane, adsorbs vertically at the water surface with its long axis normal to the surface. This vertical molecular orientation facilitates the formation of intermolecular and nonconventional dihydrogen bonds such as the B-H(δ-)···(δ+)H-C bond that has recently been proven to be at the origin of the self-assembly of MCs in water. Therefore, it appears here that lateral dihydrogen bonds are also involved in the surface activity of MCs.

Second harmonic generation at liquid interface: molecular organization, supramolecular assemblies, and chirality

Second Harmonic Generation (SHG) was used to study the optical properties of molecular films formed at liquid interfaces (air-water or dodecane-water interfaces). The technique was applied to a two-dimensional film of hemicyanine molecules: dye (4-(4-dihexadecylaminostyryl)-N-methylpyridinium iodide) (DiA) and 4-(4-(diethylamino)styryl)-Nmethylpyridinium iodide (sDiA). First, at the air-water interface, the SHG intensity was measured as a function of the incident fundamental and outgoing harmonic wave polarization. The orientation of the molecules was determined by the analysis of the polarization plots. Secondly, the adsorption of sDiA at the dodecane-water interface was characterized by the SHG technique. Finally, in the case of DiA molecules, the formation of aggregates at the air-water interface was monitored by the analysis of SHG intensity fluctuations.

Second-Harmonic Scattering in Layered Double Hydroxide Colloids: A Microscopic View of Adsorption and Intercalation

The interaction of methyl orange dye with a layered double hydroxide colloidal material is investigated using real-time polarization-resolved second-harmonic scattering (SHS). Interlayer charge compensating anion exchange is studied from initial carbonate or nitrate anions to methyl orange negatively charged dye. A theoretical model, taking into account the field retardation effect, is presented to simulate the polarization-resolved SHS experiments. Various geometrical dye configurations inside or around the host material have been modeled. A comparison with the experimental data permits to give a microscopic description of the dye organization and its time evolution during the intercalation process in the material.