Effect of protonation on the photophysical properties of meso-tetra(sulfonatophenyl) porphyrin

We present an experimental investigation on the photophysical properties of meso-tetra(sulfonatophenyl) porphyrin (TPPS4) in its bi-protonated and deprotonated states in water solutions at pH 4.0 and 7.0, respectively. The Z-scan technique at 532 nm with single 70 ps pulses as well as with pulse trains, was used in association with other complementary techniques such as UV–Vis absorption spectroscopy and time resolved fluorescence. The saturation behavior and the time evolution of nonlinear optical absorption were analyzed with a five-energy-level diagram. Photophysical parameters such as ground and excited states absorption cross-sections, together with the fluorescence lifetime and intersystem crossing time were determined.