Monolayer studies on an acetic acid substituted porphyrin and its complexes with aliphatic amines or quaternary ammonium salts at the air-liquid interface

Monolayers of 5,10,15,20-tetra-4-oxy(acetic acid)phenylporphyrin (TAPP) and its complexes formed with n-octadecylamine (ODA) in molar ratios of 1:1, 1:2, 1:3, and 1:4, n-hexadecylamine (HDA) (1:4), dimethlyldihexadecylammonium bromide (DMDAB) (1:4), and tetrahexadecylammonium bromide (THDAB) (1:4) at the air-Cd2+ solution interface have been studied. The formation of the complexes was confirmed by W-vis spectra of spreading solutions and surface pressure-area (pi-A) isotherms of monolayers. pi-A isotherms of spreading monolayers and UV-vis spectra of transferred monolayers show that the molecular areas and the maxima of the Soret bands of these porphyrin complexes changed significantly and regularly with the: mixed molar ratios and the different mixed species. However, the porphyrin ring orientation angles that were measured by linear dichronic measurements are similar for TAPP and the complexes in different monolayers. These results indicate that the number and the length of the attached alkyl chains on the porphyrin periphery have no influence on the orientation of the rings, but have great influences on the organization of the rings. Brewster angle microscopy (BAM) observations show different monolayer behaviors for these systems, indicating that the introduction of aliphatic amines or quaternary ammonium salts greatly affects the intermolecular interactions.