Exploring the locations of different groups of a cationic surface-active 3H-indole probe molecule in AOT-based water-in-oil microemulsions

We report herein the spectral and photophysical studies of the locations of different groups of a probe molecule, i.e., [2-(p-hexylamino)phenyl-3,3-dimethyl-5-ethoxycarbonyl-3H-indole]methyldioctadecylammonium iodide (1) in the microemulsion of sodium bis(2-ethylhexyl)sulfosuccinate (AOT). Two models were suggested: (1) the aliphatic chains, the hexyl group together with the part from the amino nitrogen to indolic nitrogen penetrate into the interface of the microemulsion, while the part from the indolic nitrogen to the right side resides outside the interface; (2) the aromatic main chain of 1 lies flat at the inner interface. The measured spectral characteristics, micropolarity, and fluorescence lifetime of 1 support the two models.