Organization of a new tetraalkynyl porphyrin by the Langmuir-Blodgett technique

A new tetraalkynyl porphyrin: the meso-tetra(trimethylsilylethynyl)-beta-tetra(acetic acid)porphyrin, abbreviated as H2P1, has been synthesized and organized by the Langmuir-Blodgett technique. When spread alone on pure water, it spontaneously stacks in a herringbone manner. Different methods have been used to break the pi-pi interactions and favor a flat-on anchoring of the macrocycle onto the water surface. Stable Langmuir and Langmuir-Blodgett films have been thus obtained and characterized by UV and IR spectroscopies and X-ray diffraction. A first method consists in introducing divalent cations into the subphase. It leads to an almost planar arrangement with a tilt angle of the macrocycle of ca. 15 degrees. Another approach consisting in mixing a H2P1/tricosylamine complex with methyl eicosanoate was also tried. An optimal proportion of 1:4:10 was found, leading to a tilt angle of ca. 25 degrees.