Effect of zinc cations on the kinetics for supramolecular assembling and the chirality of porphyrin J-aggregates

Dilute aqueous solutions of anionic meso-4-sulfonatophenyl-porphyrin (TPPS) extract zinc(II) ions from glass or quartz surface at room temperature and efficiently form the corresponding metal complex (ZnTPPS). The partial or complete formation of ZnTPPS has been probed by UV/Vis spectroscopy and both static and time-resolved fluorescence. The source of zinc(II) ions has been clearly identified through Inductively Coupled Plasma Optical Emission Spectrometry. The presence of increasing amounts of ZnTPPS slows down the rate of TPPS J-aggregate formation in acid solution, influencing the nucleation step and has a profound impact on the onset of chirality in these species. This evidence points to an important role of this adventitious metal ion in the interpretation of various spectroscopic and kinetic data on the self-assembly of the TPPS porphyrin and provides some insights into controversial findings on their chirality. The use of this metal derivative as starting compound to in situ formation of monomeric TPPS is suggested.