Formation of J-Aggregates of 21-thia-5,10,15,20-tetra-(4-sulfonatophenyl)-porphyrin in Acidified Aqueous Solutions

The formation of Jaggregates of 21-thia-5,10,15,20-(tetra-4-sulfonatophenyl)-porphyrin in acidified aqueous solutions is reported for the first time. The spectral-luminescent properties of these species were measured and ascribed to excitonic interactions. The number of coherent interacting monomeric porphyrin molecules in the aggregate was determined. J-Aggregates of this heteroporphyrin were found to fluoresce. The fluorescence quantum yield Φ fl was found to be 1.8·10 –4 . The J-aggregates were found to be photolabile. Upon their photo-excitation to the absorption band at 503 nm, these species collapse to the monomeric doubly-protonated molecules. The photomonomerization process is reversible: the J-aggregates form again upon maintenance of the solution in the dark.