Competition of Major Forces Dominating the Structures of Porphyrin Assembly

Abstract

Here we take the self-assembly of porphyrin molecules as an example to discover the reason for the diversity of assembled structures. The self-assembly is conducted at a range of pH conditions. Irregular, tubular, and rodlike particles are formed at pH 1.5, 6.5 and 12.5, respectively. X-ray diffraction spectra and UV absorption show that these particles have the same crystalline structures, while the packing types of molecules are different. At low pH, the molecules assemble together by end to end attachment with a J-type aggregation, forming irregular particles. This assembly is dominated by the competition of π–π interaction and repulsion force. The latter force is induced by the protonation of molecules under acid conditions. With the increase of pH, the repulsion force is attenuated and finally disappears under basic conditions. The π–π interaction becomes the major force under basic conditions, leading to a H-type aggregation via face to face attachment and forming rodlike particles. At the middle pH...