Ink-Free Reversible Optical Writing in Monolayers by Polymerization of a Trifunctional Monomer: Toward Rewritable Molecular Paper

A Langmuir-Blodgett film consisting of a dense array of trifunctional monomers bearing three 1,8-diazaanthracene units is polymerized at an air/water interface or after transfer on solid substrates. The transfer does not affect the excimer fluorescence of the film, indicating that the monomers' packing with their diazaanthracene units stacked face-to-face is retained-a prerequisite for successful polymerization. The monomer film can be polymerized in confined areas on solid substrates by UV irradiation with a confocal microscope laser. The underlying chemistry of the polymerization, a [4+4]-cycloaddition of the diazaanthracene units, leads to disappearance of the fluorescence in the irradiated regions which enables writing into the monolayer on a mu m scale-thus the term molecular paper. The reaction can be reversed by heating which leads to a recovery of the fluorescence and to erasing of the writing. Alternative pathways for this phenomenon are discussed and control experiments are conducted to rule them out.