Phosphoniumyl cationic porphyrins - Self-aggregation origin from pi-pi and cation-pi Interactions

The electrospectroscopic properties of four cationic porphyrins possessing phosphoniums residues in the periphery of the porphyrin plane are investigated in aqueous and organic solvent phases. The electronic spectra of the phosphoniumyl porphyrins in pure water and in the presence of inorganic and organic electrolytes are compared, and it is proposed that self-aggregation of the phosphoniumyl porphyrins arises from pi-pi interaction forming H-aggregates and that this geometry can be transformed into J-aggregates by cation-pi interaction between the porphyrin plane and the peripheral phosphonium cations on addition of NaCl. H-1 NMR spectra provide evidence that the highly polarizable phosphonium cation interacts strongly with the highly polarizable porphyrin pi-surface.