Formation of J-Aggregates of the 21-Thia-5,10,15,20-Tetra-(4-Sulfonatophenyl)-Porphyrin in Water Solutions

Abstract

The formation of J-aggregates of 21-thia-5,10,15,20-tetra-(4-sulfonatophenyl)-porphyrin in acidified water solutions is herein revealed for the first time and their spectral-luminescent properties are measured. It is shown that the spectral-luminescent properties of J-aggregates are due to the excitonic interactions, and the number of coherent interacting monomeric porphyrin molecules in the aggregate is evaluated. It is found that J-aggregates of heteroporphyrin have fluorescence, and the fluorescence quantum yield Фfl is found to be as low as 1.8 × 10^–4. The photolability of J-aggregates is found, namely, upon J-aggregate photoexcitation to the absorption band at 503 nm they collapse to the monomeric doubly protonated molecules. The process of photomonomerisation is reversible: upon keeping the solution in the dark, J-aggregates form again.