Effects of NaCl upon TPPS4 triplet state characteristics and singlet oxygen formation

The quantum yield (φT) and lifetime (τT) of the triplet state (T) of water-soluble meso-tetrasulphonatophenyl porphyrin (TPPS4) and the kinetic profile and quantum yield (φO21) of the singlet oxygen 1O2, produced due to the energy transfer from T to molecular oxygen, were investigated for biprotonated (pH 4.0) and non-protonated (pH 7.0) TPPS4 forms as a function of the NaCl concentration. The study was performed with the help of flash-photolysis technique compared with the data obtained by optical absorption spectroscopy. The 1O2 characteristics were monitored by kinetics and spectrum of its infrared phosphorescence.As shown, for biprotonated TPPS4 the addition of NaCl reduces both φT and τT due to two processes: “quenching” by Na+ and/or Cl− ions and successive formation of H and J TPPS4 aggregates. The triplet state formation for the porphyrin J aggregates was detected. For non-protonated TPPS4, no aggregation in the presence of salt occurs and the observed reduction of φT and τT was due to the interaction with Na+ and/or Cl− ions. The reduction of φT was accompanied by the simultaneous reduction of (φO21). No NaCl effects on the quenching constant of T by O2 and on the 1O2 lifetime were observed.