Effect of the interface on the photophysics of eosin-Y in reverse miceles

The photophysics of the xanthene dye eosin-Y (Eos) was studied in reverse micelles (RMs) of sodium 1,4-bis (2-ethylhexyl) sulfosuccinate (AOT) and benzylhexadecyldimethylammonium chloride (BHDC). Special interest was assigned to the effect of organization on the triplet state properties. In the reverse micellar media both the absorption and emission spectra of the dye present a red shift with respect to water. It is concluded that Eos in both reverse micellar systems is localized in the interface. Although this is predictable in BHDC due to the positive charge at the interface and the negative charge of the dye, it is notable in the case of the negative interface of AOT. In this case it may be concluded that Eos resides in the interface co-micellizing with the surfactant, although more exposed to water than in the case of BHDC. Triplet state decay kinetics and absorption spectra were determined by laser flash photolysis. The triplet lives longer in RMs than in homogeneous solvents. The compartmentalization of the dye precludes the auto-quenching which shorts the lifetime in homogeneous solvents. The quenching by aliphatic amines was also investigated. The hydrophilic triethanolamine (TEOA) is localized in the water pool, and the triplet quenching is more efficient than in homogeneous solvents. On the other hand the quenching by tributylamine (TBA) which is located in the bulk organic solvent is much less efficient. The quenching by TEOA in RMs can be understood in terms of an exchange mechanism between micelles. Quantum yields of radicals produced in the triplet quenching process were determined.

► The photophysics of Eosin-Y was investigated in reverse micelles (RMs) of AOT and BHDC. ► The dye molecules remain at the interface sensing a less polar medium in the case of BHDC. ► The triplet lifetime is much longer in the RMs than in homogeneous organic solvents. ► Apparent triplet quenching rate constants by tri-ethanolamine (TEOA) and tri-butylamine (TBA) were determined in MeOH and in RMs. ► Triplet quenching by TEOA is near two orders of magnitude more effective in AOT than in homogeneous solution.