Protoporphyrin IX Zinc(II) Organization at the Air/Water Interface and Its Langmuir−Blodgett Films

Protoporphyrin IX zinc(II) (ZnPP) and its mixtures with N-hexadecylethylenediamine, hexadecyltrimethylammonium bromide, and didodecyldimethylammonium bromide in a molar ratio of 1:2 were used to investigate the Langmuir monolayer and Langmuir−Blodgett (LB) film behaviors. The well-defined Langmuir monolayers were formed at the air/water interface for ZnPP alone and its hybrids with surfactants. While the ultraviolet−visible spectrum of ZnPP alone indicated the formation of an H-aggregate in the LB film from the blue shift of the Soret band, the introduction of surfactants into the ZnPP LB film reduced the π−π interaction between ZnPP macrocycles. Linear dichroism revealed that the average orientation angle of the protoporphyrin macrocycle against the substrate surface was in the range of 39.5−44.5° in a ZnPP LB film and three ZnPP/surfactant LB films. Fourier transform infrared spectra of the LB films suggested that the alkyl chains of the surfactants take a disordered gauche conformation and porphyrin ca...