Aggregation behavior of tetrakis (4-sulfonatophenyl) porphyrin in the inner water pool of inverse microemulsions

TX-100/n-hexanol/water/cyclohexane inverse microemulsions were used to entrap tetrakis(4-sulfonatophenyl)porphyrin(TPPS). The aggregation behavior of TPPS in the inner phase of nonionic W/O inverse phase was investigated on changing pH, the size of the microemulsions[w(0) = n (H2O)/n (TX-100)] and the concentration of porphyrin. The apparent pK(a) of TPPS in a microemulsion was found to be much lower than that in an open aqueous solution, and exhibited a decrease on decreasing the w(0) value. Deprotonized TPPS was prevalently presented when pH > pK(a). While the main species J-aggregates and protonized TPPS existed when pH < pK(a), and more protonized TPPS self-assembled into J-aggregates on increasing the concentration of TPPS. At fixed pH, the deprotonized TPPS tended to become protonized and self-assembled into J-aggregates on increasing the inner water pool dimension (w(0) value).