Unusual aggregation behavior of porphyrin dye tetrakis (4- sulfonatophenylporphyrin) within aqueous deep eutectic solvents

Abstract

Aggregation behavior and photophysics of an anionic porphyrin dye named tetrakis(4-sulfonatophenyl)porphyrin (TPPS) was studied first time in four different choline chloride based deep eutectic solvents (DESs) i.e., reline, ethaline, glyceline, and maline. In three DESs (reline, ethaline, and glyceline), TPPS mainly remains in monomer form with minute J-aggregates. However, in fourth DES maline, a completely different behavior was observed where TPPS formed extended J- and H-aggregates. Further, effect of change in pH and role of water as additive was assessed through UV–vis molecular absorption and fluorescence emission spectroscopy. It is important to note that pH change showed no effect on TPPS spectra in maline, whereas, addition of water was found to disrupt both J- and H- aggregates. © 2025 Elsevier B.V.