Influences of hydrophilic and hydrophobic substituents on the organization of supramolecular assemblies of porphyrin derivatives formed at the air/water interface

Monolayers and Langmuir–Blodgett (LB) films of several kinds of porphyrin derivatives that have different substituted alkyl chain length, chain numbers and central metals were studied by π-A isotherms, UV–Vis, polarized UV–Vis and fluorescence spectroscopy and low angle X-ray diffractometry (LAXD). The orientation angles of porphyrin rings and alkyl chains were derived from the polarized UV–Vis spectra and LAXD patterns of the monolayers or LB films, respectively. The rings of the freebase porphyrins with different alkyl chain length or number have similar orientation angles in the films due to the same hydrophilic groups on the rings, and those of metal porphyrins have different orientation angles from each other. The orientation of the alkyl chains is related to the special positions of the chains on the rings and the orientation of the rings. The influences of the hydrophilicity of the hydrophilic groups and the alkyl chain number and length on the organization of the supramolecular assemblies of the porphyrin derivatives were discussed.