Specific dye adsorption at oriented monolayers

Abstract

We studied the adsorption of water soluble cyanine dyes (pseudoiso-cyanine and “stains-all”) to monomolecular layers of arachidic acid at the water-air interface in a Langmuir trough. Fluorescence microscopy was employed to on-line monitor the formation of J-aggregates upon adsorption. Large two-dimensional monodomain single crystals could be grown by this self-assembly process with optical properties reminiscent of those found and extensively studied for amphiphilic derivatives of the same chromophors [12]. In addition to the necessary Coulombic interaction between subphasedye and target monolayer, we found that details of the crystal morphology also crucially depend on substrate parameters, e.g., the packing density during adsorption. After transfer of the monolayer to a hydrophobic solid support, either as a Langmuir-Blodgett film or in a flow cuvette, i.e., still in contact with the aqueous phase, absorption spectroscopy as well as fluorescence spectroscopy and -microscopy was employed to characterize the adsorbate stability, its desorption, re-adsorption or exchange reactions.