Excited-state absorption of meso-tetrasulfonatophenyl porphyrin: Effects of pH and micelles

• Excited-states spectra of porphyrin (S1 → Sn and T1 → Tm) were obtained.
• It was employed UV/Vis absorption, flash photolysis and Z-scan techniques.
• Molecular symmetry can be preserved upon excitation.
• Distortion of porphyrin ring has great influence on singlet and triplet states.
• TPPS porphyrin is a promising candidate for optical limiting applications.

The influence of the environment on the excited state transitions of meso-tetrakis(p-sulfonatophenyl) porphyrin (TPPS) is reported. TPPS was investigated in protonated and non-protonated forms, and in the presence of the cationic cetyltrimethylammonium bromide (CTAB) micelles. The singlet excited-state absorption spectra were measured by using the white-light continuum Z-scan technique and the triplet–triplet absorption spectra were acquired employing an association of laser flash photolysis and Z-scan techniques. Our results show that the perseveration of the molecular symmetry, upon excitation, depends on the state of multiplicity of the molecules, as well as on the environment and structural characteristics of the porphyrin. Additionally, it was observed that for excited molecules, the ring distortion caused by the protonation of porphyrin ring has great influence on the changes observed for the symmetry and vibronic structure. The results clearly show that the porphyrin investigated is a promising candidate for optical limiting applications for all investigated environments.