Langmuir–Blodgett films of a polymerisable N,N'-disubstituted dithiooxamide coordination compound

The monolayer properties of the amphiphile N,N'-bis(10,12-pentacosadiynyloxycarbonylmethyl)dithiooxamide at the air–water interface were studied by measuring surface pressure–area isotherms. The amphiphile itself does not form stable monolayers on an aqueous subphase but when Cu(II) ions are added to the subphase a coordination polymer is formed, which forms stable monolayers at the air–water interface. The monolayer stability is strongly influenced by the counterion, pH and temperature of the subphase. Electron microscopy shows that at a low surface pressure (about 2 mN m-1) a monolayer of loosely packed islands is formed. When the surface pressure has increased a more homogeneous monolayer is formed with small holes which disappear when the monolayer is stabilised at a constant surface pressure for a few hours. The monolayers of the coordination polymer can be transferred onto solid substrates by a Y-type transfer. The presence of Cu(II) ions is confirmed by XPS measurements and UV/Vis spectroscopy shows a strong absorption at 370 nm, indicating that a strongly conjugated coordination polymer is formed at the air–water interface. SAXR measurements reveal that the LB films have a rather irregular layer structure and upon exposure to UV light, the diacetylene groups are only partly converted to polydiacetylene; moreover, the coordination polymer is partly destroyed.