Luminescence of zinc tetraphenylporphyrin in ethylene glycol-in-oil microemulsions

Photophysical properties of zinc-tetraphenylporphyrin (ZnTPP) were studied in n-heptane/AOT/ethylene glycol and isooctane/AOT/ethylene glycol microemulsions. Results of steady state and transient fluorescence techniques show the existence of different spectroscopic ZnTPP species located at different environments of the reverse micelles. The behavior of such species depends on the molar ratio [ethylene glycol]/[AOT]. Upon addition of ethylene glycol to the medium, a large displacement of ZnTPP molecules from the apolar bulk to the polar phase takes place due to the existence of a "strong" interaction between the polar solvent and the Zn metal ion (solvation type). The equilibria of ZnTPP between the different environments was quantified from absorption and emission spectra.