Architecture and Surface Properties of Monomolecular Films of a Cyanine Dye and Their Light-Induced Modification

Abstract

Monolayers of a water-insoluble cyanine dye are deposited on negatively charged substrates such as glass, mica, or a thin film of a poly(acrylic acid) (PA) by adsorption from a solvent in which the dye is scarcely soluble. The choice of the substrate has a strong influence on the architecture of the dye layers. A submonolayer coverage of the monomeric dye is formed on PA, whereas a complex layer structure of J-aggregated dye molecules is formed on mica. The dye layers on mica have different affinities for the adsorption of charged colloidal particles and macromolecules. Photooxidation of the dye yields a water-soluble product. This photochemical reaction is the basis for forming surface structures of different reactivity by photopatterning of the dye layers. After photopatterning the bleached dye is dissolved in water. Conditions were found where macromolecules or colloidal particles adsorb preferentially either to exposed or to unexposed areas of photopatterns on a mica substrate.