The effect of cations(H +,Li +,Na + and K +) on the J aggregation of tetrakis( p sulfonatophenyl) porphyrin diacid (H 2+ 4TSPP 4- ) was studied by UV Vis absorption spectra.It was demonstrated that the presence of these cations promotes the J aggregation of H 2+ 4TSPP,implying that the external cations are necessary to balance the Coulomb repulsion between the sulfonate groups of adjacent H 2+ 4TSPP 4- molecules in the J aggregate.The excitionic energy of the J aggregate was evaluated under the dipole dipole interaction,which is qualitatively consistent with the experimental result.The results support the staircase structural model of the aggregate.
