Anisotropic growth of J aggregates of pseudoisocyanine dye at a mica/solution interface revealed by AFM and polarization absorption measurements

We investigated the J-aggregation process of pseudoisocyanine chloride at a mica/solution interface by using tapping mode atomic force microscopy (TM-AFM) and polarization absorption measurements. At a mica/solution interface, pseudoisocyanine chlorides form J aggregates that have three-dimensional leaf-like island structures. The islands are anisotropically oriented with respect to the lattice of a mica substrate. This anisotropic alignment may result from the epitaxial interaction between the positively charged N atoms of the molecules and the regularly aligned negative holes left by the dissociating K+ ions. On the basis of both the orientation of islands to the lattice of a mica and the epitaxial interaction, we proposed that in the internal structure of the J aggregate, the long axis of the dye molecules is parallel to the long axis of the islands.