Morphological control of the supramolecular pseudoisocyanine J-aggregates by the functions of a mica/solution interface

The effect of a mica/solution interface on the formation of supramolecular pseudoisocyanine chloride (PIC-Cl) J-aggregates was investigated by AFM observing the morphology and alignment of the J-aggregates relative to a mica surface upon applying a PIC-Cl solution onto a mica surface. When a PIC-Cl solution was placed directly on freshly cleaved mica (Method 1), the resulting J-aggregates formed leaf-like islands that are anisotropically oriented with respect to the lattice of a mica substrate. These anisotropic alignment might results 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 during the nucleation process. Based on their epitaxial interactions, the supramolecular structure of the J-aggregate has been proposed that the long axis of PIC-Cl molecules is parallel to the long axis of the island. In contrast, when a PIC-Cl solution was poured onto an aliquot of pure water already present on the mica surface (Method 2), the J-aggregates formed streaks of needle-like islands that were oriented in only one direction which corresponded well to the stream of the poured PIC-Cl solution. Based on these results, possible aggregation mechanisms were proposed where the stream of the solution is participating. It is revealed for the first time that both the morphology and alignment of the J-aggregate islands relative to a mica surface can be controlled by how the PIC-Cl solution is applied onto the mica surface.