Amphiphilic porphyrins in reverse micelles: the influence of the molar ratio of water to surfactant and side-chain length on their triplet-state lifetimes. A case study

Abstract

Using bis(2-ethylhexyl) sodium sulfosuccinate (AOT) as surfactant, a series of amphiphilic porphyrins terminated with imidazole were studied in AOT/isooctane/water reverse micelles, intending to mimic the relationship between microenvironments in organisms and the amphiphilic properties of porphyrins for photodynamic therapy (PDT) applications. Laser flash photolysis experiments and fluorescence quenching of porphyrins by phenothiazine show that longer side-chain lengths and higher molar ratio of water to AOT (w_o) of reverse micelles promotes firm embedding of porphyrin molecules in the interfacial region of reverse micelles. Such an embedding may shift porphyrins from aggregated to monomeric form in reverse micelles and, accordingly, the slower excited-state decay may increase the efficiency of the photosensitizer in PDT. The variation in the ability of singlet oxygen generation detected by ESR also supports such a conclusion. The effect of amphiphilic properties on the status of porphyrins in microenvironments provides light on the synthesis of other amphiphilic porphyrins for PDT applications.