The molecular aggregation state of a porphyrin-perylenediimide dyad can be changed by treating with trifluoroacetic acid. Transmittance electron microscopy (TEM) images revealed that lamella micro- structures were formed when the dyad precipitated from neutral solvent, but spherical nano-particles were obtained when precipitating from acidic solution. X-ray diffraction patterns showed that the la- mella microstructures and the nanoparticles were polycrystalline and amorphous solids, respectively. By using rational perylenediimide and porphyrin as reference compounds, careful analyses on the UV-visible spectra of the dyad and the references under different conditions were conducted and the results demonstrated that both the porphyrin and perylendiimide subunits of the dyad took J-aggregation in neutral solvent, but after being treated with trifluoroacetic acid and chloroform solu- tion, the perylenediimide subunit changed to an H-aggregation while the porphyrin subunits changed to a random packing mode.
