Langmuir–Blodgett multilayers of six compact porphyrin amphiphiles

Abstract

By a modification of the Jackson–MacDonald condensation between two symmetrically substituted dipyrrylmethanes, we have synthesised two porphyrin free-base amphiphiles and four metalloporphyrin amphiphiles all of which serve as models for the naturally derived product mesoporphyrin IX dimethyl ester. These compounds have different substituents along their hydrophobic edge to those found in mesoporphyrin IX, which has the sequence Me, Et, Me, Et. Our materials have the sequences (Me)₄ or (Et)₄ thus making the hydrophobic edge slightly larger, or slightly smaller than that contained in mesoporphyrin IX.

Upon an aqueous subphase, Langmuir films were obtained at pressures in the range 14–50 mN dm³ mol^–1, with, at full compression, molecular areas of the order of 65 Ų and angles-of-tilt of the macrocyclic plane to the subphase of some 80°. LAXRD data were taken on Langmuir–Blodgett multilayer films of the (Et)₄ compounds which proved to have the threshold minimum magnitude of hydrophobic edge for multilayer formation, with Y-type bilayers being given by the zinc and silver complexes.