Interactions between a surface-active cationic 3H-indole molecular probe and micellar environments

We report herein the interactions of a cationic surface-active molecular pr obe having long aliphatic chains, i.e., [2-(p-hexylamino)phenyl-3,3-dimethy l-5-ethoxycarbonyl-3H-indole]methyldioctadecylammonium iodide (1), with SDS (sodium dodecyl sulfate) and CTAB (cetyltrimethylammonium bromide) micelle s investigated by spectral and photophysical characterizations. According t o the absorption and fluorescence spectral characteristics and the fluoresc ence quantum yield, the interaction of 1 with SDS exhibits different patter ns that depend on the SDS concentration: (1) formation of ion-pairs at very low concentration of SDS; (2) complex coacervation below the critical mice llar concentration (c.m.c.) of SDS; (3) solubilization of the coacervate ph ase into micelles above the c.m.c. The fluorescence quantum yield measureme nt as well as the pH effect studies reveal that the hexyl group and a part of the anilino moiety of 1 penetrate the micellar interface, while the indo lic moiety of 1 resides in the bulk phase. Lifetime measurements support th e existence of three interaction patterns between 1 and SDS, and further in dicate that 1 recognizes one location in the SDS micelle and two in the CTA B micelle.