Chemical Reactivity in Monolayers: Study of an Amphiphilic Tetrapyridinoporphyrazine in Langmuir-Blodgett Films
Résumé
This paper reports on the synthesis, association in solution, monomolecular layer formation, and Langmuir-Blodgett (LB) homolayer and alternate layer properties of an amphiphilic copper tetrapyridinoporphyrazine. The high conjugation of the four pyridinium rings with the central porphyrazine core has a great influence on the chemical properties in solution and in a monolayer. The degree of association is dependent on the Lewis acidity of the solvent, the oligomeric forms-stable in pure chloroform solution--being broken by any donor-acceptor interaction between the porphyrazine ring and Lewis acids such as acetic acid, nitrogen dioxide, or iodine. The amphiphilic porphyrazine forms stable monomolecular layers to film pressure up to 35 "am-'. The aromatic ring reacts with water, giving rise to a virtually two-electron-reduced porphyrazine through a donor-acceptor complex. This complex can be transferred onto solid substrates and is indefinitely stable in LB films. It is characterized by infrared, electronic, and ESR spectroscopy. The chemical reduction in the monolayer state is inhibited by Lewis acids present either in the bath or in the monolayer. ESR studies on homolayers and alternate layers built from mixtures of the amphiphilic porphyrazine and w-tricosenoic acid show that the porphyrazine rings lie flat on the substrate, and provide an estimation of the plane-to-plane and in-plane coupling between the copper ions