Cl- Complexation Induced H- and J-Aggregation of meso-Tetrakis(4-sulfonatothienyl)porphyrin Diacid in Aqueous Solution

Various porphyrin diacids are known to show controlled self-assembly by inorganic anions. Following the unexpected finding that meso-tetrakis(4-sulfonatothienyl)porphyrin diacid shows Cl- specific aggregation in spite of having the anionic substituents, the aggregation behavior of the diacid in aqueous solution with Cl- was investigated in detail. We found that Cl- induces the H-aggregate, followed by the transformation into the J-aggregate with increasing Cl- concentration. For the J-aggregate formation, negatively charged sulfonic acid groups were suggested to be of minor influence. The J-aggregate forms nanoscale macrostructures composed of highly oriented molecules on substrate. To our knowledge, this is the first report of both H- and J-type aggregate formation of a porphyrin diacid in the presence of an aqueous inorganic anion. These results would open the gate for controlling the chromophore packing structure of a porphyrin diacid complexed with an inorganic anion by varying the composition.