Fluorescence quenching of a squaraine dye by water in AOT reversed micelles

Abstract

The photophysics of a fluorescent probe bis[4-(dimethylamino)phenyl]squaraine (HSq) was studied in AOT water-in-oil microemulsions, using steady-state and transient (picosecond resolution) techniques. The interaction of HSq with water occurs only in the excited state and is reaction controlled with a bimolecular rate constant of k_q=3.87×10⁸M^-1 s^-1 accounting for the nonradiative processes. The kinetic data obtained in AOT reversed micelles were treated assuming two distinct spectroscopic species located in the interfacial region that were equally quenched by the water present in their vicinity with the same rate constant. The parameters obtained enable the distinction of processes occurring in the hydrophobic and hydrophilic interfacial domains and the estimation of the number of water molecules per AOT molecule in each domain, respectively three and nine.