Subtleties of Catanionic Surfactant Reverse Micelle Assemblies Revealed by a Fluorescent Molecular Probe.

In this work, the absorption and emission behavior of the cationic hemicyanine trans-4-[4-(dimethylamino)styryl]-N-methylpyridinium iodide (HC) in reverse micelles (RMs) formed by the catanionic surfactants: benzyl-n-hexadecyldimethylammonium-1,4-bis-2-ethylhexylsulfosuccinate (AOT-BHD) and cetyltrimethylammonium-1,4-bis-2-ethylhexylsulfosuccinate (AOT-CTA) has been investigated. Our results show that the HC spectroscopic behavior changes when the dye is dissolved in AOT-BHD or in AOT-CTA RMs. While HC undergoes an intramolecular charge-transfer process upon excitation in AOT-CTA RMs, in AOT-BHD RMs this process is inhibited due to a specific interaction between HC and the polar head group of the BHD+ cation. This implies that the chemical structure of CTA+ and BHD+ cations has great impact on the excited stated from which HC emission occurs. Additionally, the structural difference between both cations impacts on the water-RM interface interaction, which provides a way to have control on the solvation process in these RMs. Furthermore, differences in the interfacial fluidity between both catanionic RMs is observed, result particularly interesting if these systems want to be used as nanoreactors.