J- and H-aggregates of 5,10,15,20-tetrakis-(4-sulfonatophenyl)-porphyrin and interconversion in PEG-b-P4VP micelles

Micellization of poly(ethylene glycol)-block-poly(4-vinylpyridine) (PEG114-b-P4VP61) induced by 5,10,15,20-tetrakis-(4-sulfonatophenyl)-porphyrin (TPPS) in acidic solutions were studied by dynamic and static light scattering, atomic force microscope, and UV-vis spectroscopy. The resultant complex micelles had a core-shell structure with the electrostatically complex TPPS/P4VP as the core and the soluble PEG as the shell. The anionic TPPS in the micellar core formed J-aggregates at pH 1.5-2.5 and H-aggregates at pH 3.0-4.0, respectively. Interconversion between the J-aggregates and the H-aggregates was carried out by adjusting the pH value of the micelle solutions. It is worth noting that the micelles showed strong split Cotton effect in the circular dichroism spectra although TPPS and the copolymer were all achiral. The resulting chirality sign could be selected by the hydrodynamic forces of a stirring vortex. Positive or negative chiral signals appeared when stirring clockwise or anticlockwise.