Change in aggregation state of a porphyrin-perylene-diimide dyad induced by trifluoroacetic acid

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 microstructures 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 lamella 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 solution, the perylenediimide subunit changed to an H-aggregation while the porphyrin subunits changed to a random packing mode.