Fluorescence behaviour of 4-[5-(2-phenyloxazolyl)] benzenesulfonic acid and N-hexyl-4-[5-(2-phenyloxazolyl)] benzenesulfonamide in homogeneous micellar and microemulsion systems

The fluorescence and excitation spectra of 4-5-(2-phenyloxazolyl)]benzenesulfonic acid (PPOS) and N-hexyl-4-5-(2-phenyloxazolyl)] benzenesulfonamide (PPOSA) were investigated in homogeneous solutions of varying polarities (hexane, heptane, butanol and water) and in aqueous micellar systems of anionic surfactants (bis(2-ethylhexyl)sulfosuccinate, sodium salt (AOT), sodium dodecyl sulfate (SDS)) and cationic surfactants (benzyldimethylhexadecylammonium chloride (CDBA), hexadecyltrimethylammonium chloride (CTAB)). These compounds were also investigated in different oil-in-water (o/w) and water-in-oil (w/o) microemulsions of the system composed of SDS, n-butanol, cyclohexane and water. The results revealed that the two probes exhibit pronounced spectral changes in response to the changes in the polarity of the medium, and in hydrophobic—hydrophilic interactions. The spectral behaviour of PPOS and PPOSA in micellar systems indicates that these two probes are incorporated at the interface of the cationic micelles. In microemulsions, however, the probes exhibit different Stokes shifts compared with those found for homogeneous solutions, indicating different salvation processes of both the ground and the excited states.