Preparation of Langmuir-Blodgett “built-up” multilayer films of a lightly substituted model aromatic, anthracene

It is generally considered almost impossible to make Langmuir-Blodgett “built-up” multilayer films of conjugated (aromatic) molecules unless their aromaticity is very heavily diluted with aliphatic substituents or molecules; this severely limits the scientific and technological applications of such films. For example, even to handle anthracene-derivative monolayers on water (without any attempt to transfer them to a substrate) has in the past required the anthracene to be substituted with an aliphatic side chain containing at least twelve carbon atoms; this prevents instability of the water-borne monolayer. As a result, the interesting and useful electrical and optical properties which conjugated multilayers would be expected to possess (because of the extended molecular π electron systems) are heavily diluted by aliphatic properties. We now report the successful deposition of high quality multilayers of lightly substituted anthracene derivatives, with aliphatic side chains as short as four CH₂ units. Improved techniques may well permit even shorter side chains to be used. We describe the deposition methods in detail and give experimental evidence that high quality films from one monolayer thick (about 1.5 nm) to 500 monolayers were indeed obtained; the interesting electrical and optical properties of these films, and their unique structure, will be discussed in detail at a later date. If these preparation techniques can be extended to other conjugated systems, as seems likely, the range of highly organized structures which can be constructed by the Langmuir-Blodgett method has been greatly increased, and the prospects for its technological use (in applications ranging from electronic devices to high temperature superconductors) have been improved.