Langmuir films and Langmuir-Blodgett multilayers incorporating mechanically-threaded molecules - Pseudorotaxanes

This paper describes the synthesis of a π-electron rich aromatic lipid containing a polyether thread intercepted by a 1,5-dioxynaphthalene moiety. The terminus of one end of the polyether is a methoxyl group and the other a glycerol unit linked via the 2-oxo position, while the 1,3-oxo functions are covalently attached to octadecyl chains. This compound, when cospread at the air-water interface with the tetracationic cyclophane, cyclobis(paraquat-p-phenylene), and the phospholipid, dimyristoylphosphatidic acid, as its monoanion, forms self-assembled pseudorotaxanes which are self-organized into a two-dimensional supramolecular array at the interface. The electrostatic interactions between the tetracationic cyclophane and the monoanions of the phospholipid anchor the cyclophane to the interface. This anchoring allows the naphthalene moiety to remain threaded through the cavity of the cyclophane by a combination of charge-transfer and hydrogen-bonding interactions. These Langmuir films can, subsequently, be transferred to a quartz support to fabricate Langmuir-Blodgett multilayers. In characterising these self-organized systems, surface pressure-area isotherms and surface potential measurements have been used in conjunction with fluorescence and UV-Vis spectroscopies. This research may have implications in sensor technology and molecular information storage devices.