Aggregation of TPPS on spreading films of achiral cationic amphiphiles: Effect of the charge and rigid spacer on the morphologies and supramolecular chirality

Aggregation of an anionic TPPS (tetrakis(4-sulfonatophenyl)porphine) on the spreading films of cationic amphiphiles containing one, two and four positive charges at the air/water interface were investigated. The positive charge centers in these amphiphiles were separated by a rigid spacer. It was found that TPPS in the subphase could aggregate onto the spreading films as J-aggregate. The complex films formed in situ at the air/water interface could be transferred onto solid substrate by a horizontal lifting method. Although the amphiphiles and the TPPS were achiral, CD signals were detected for the complex films. A possible helical sense of the TPPS stacked in the complex film was suggested to be responsible for the supramolecular chirality of the multilayer films. The charge distributions and spacers have great influence on the CD intensity as well as their split and the surface morphologies. AFM measurements revealed nanofiber structures in the surface morphologies for the complex films of TPPS with amphiphiles having one or two positive charges, while nanorod morphologies were observed for that with four positive charges. It was suggested that the charge centers in the amphiphiles limited the aggregation of TPPS and the interactions between the adjacent J-aggregates.