Self-assembly of acridine orange dye at a mica/solution interface: Formation of nanostripe supramolecular architectures

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Optical waveguide spectroscopy and atomic force microscopy (AFM) have been used to characterize the supramolecular architectures of acridine orange (AO) dye self-assembled at a mica/aqueous solution interface. Under the saturated adsorption conditions, optical waveguide spectroscopy revealed that the dye formed H-type aggregates at the interface. In situ AFM visualized interesting morphology of the dye aggregates showing nanosized meandering stripes with the width of ∼ 1.5 nm (or brightness periodicity of ∼ 3 nm ). Electrostatic adsorption of the dye cations onto a mica surface as well as the intermolecular π – π stacking brought about the ordered nanostructures. We propose an interfacial aggregation model that shows a meandering staircase structure with the intermolecular slip angle of 60°. According to the model, the AO molecule occupies a surface area of about 1.0 nm 2.