Herringbone structure in two-dimensional single crystals of cyanine dyes. I. Detailed structure analysis using electron diffraction

Abstract

The crystalline structure of two-dimensional aggregates of different carbocyanine molecules was investigated in detail by means of electron diffraction. The aggregates are formed by electrostatic adsorption of anionic dye molecules from an aqueous solution at a positively charged ammonium lipid monolayer. From the diffraction pattern we deduce a herringbonelike arrangement of the dye molecules as described by a centered, rectangular unit cell containing two identical molecules. The aggregate structures of the systems investigated here differ only by the mutual orientation of the molecules and the axis ratios of the unit cell. For further optical studies we determine the angle α between the main axes of the differently oriented molecules with very high precision. We calculate electron diffraction intensities of several structures which are simulated on the computer and compare them to experimental data. We observe that the dye aggregates are aligned to one of the crystal axes of the lipid lattice.