Tuning Hofmeister ion sensitivity in porphyrin J-aggregation through molecular charge density

This study investigates the self-assembly kinetics of three structurally related sulfonato-phenylporphyrins, 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS[Formula: see text], 5,10,15-tris (4-sulfonatophenyl)-20-phenyl-porphyrin (TPPS[Formula: see text] and 5,15-bis(4-sulfonatophenyl)-10,20-phenyl-porphyrin ([Formula: see text]-TPPS[Formula: see text] into supramolecular J-aggregates in acidic aqueous solutions, using a series of inorganic acids. The aggregation process, followed by UV/Vis spectroscopy, monitoring the characteristic B-band disappearance (434 nm) and the sharp, red-shifted J-band appearance (490 nm), exhibits typical sigmoidal, autocatalytic kinetic profiles. Kinetic parameters derived from Pasternack’s model reveal that TPPS 4 and t-TPPS 2 aggregation rates adhere to the Hofmeister series for anions (SO[Formula: see text] Cl[Formula: see text] Br[Formula: see text] NO[Formula: see text] ClO[Formula: see text], correlating linearly with the anions’ structure-making/breaking abilities. Notably, [Formula: see text]-TPPS 2 kinetics are an order of magnitude faster than TPPS 4 . In contrast, TPPS 3 exhibits deviations from Hofmeister behavior together with smaller critical nucleus sizes, likely reflecting its distinct nano-ribbon morphology compared with the nano-tubes/stacked platelets structures formed by the other porphyrins. This work highlights how subtle molecular changes and the ionic environment tune macroscopic material properties via non-covalent interactions.