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

Abstract

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. © 2014 SPIE.