Photochemical creation of covalent organic 2D monolayer objects in defined shapes via a lithographic 2D-polymerization

In this work, we prepare Langmuir-Blodgett monolayers with a trifunctional amphiphilic anthraphane monomer. Upon spreading at the air/water interface, the monomers self-assemble into 1 nm-thin monolayer islands, which are highly fluorescent and can be visualized by naked eye upon excitation. In-situ fluorescence spectroscopy indicates that in the monolayers, all the anthracene units of the monomers are stacked face-to-face forming excimer pairs, whereas at the edges of the monolayers free anthracenes are present acting as edge groups. Irradiation of the monolayer triggers [4+4]-cycloadditions among the excimer pairs, effectively resulting in a two-dimensional polymerization. The polymerization reaction also completely quenches the fluorescence, allowing to draw patterns on the monomer monolayers. More interestingly, after transferring the monomer monolayer on a solid substrate, by employing masks or the laser of a confo-cal scanning microscope, it is possible to arbitrarily select the parts of the monolayer that one wants to polymerize. The unpolymerized regions can then be washed away from the substrate, leaving two-dimensional macromolecular monolayer objects of the desired shape. This is the first photolithographic process that employs 2D-polymerizations and affords 1 nm-thin coatings.