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 obs erving 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 result ing J-aggregates formed leaf-like islands that are anisotropically oriented with respect to the lattice of a mica substrate. These anisotropic alignme nt might results from the epitaxial interaction between the positively char ged N atoms of the molecules and the regularly aligned negative holes left by the dissociating K+ ions during the nucleation process. Based on their e pitaxial interactions, the supramolecular structure of the J-aggregate has been proposed that the long axis of PIC-Cl molecules is parallel to the lon g axis of the island. In contrast, when a PIC-Cl solution was poured onto a n 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 o nly one direction which corresponded well to the stream of the poured PIC-C l solution. Based on these results, possible aggregation mechanisms were pr oposed where the stream of the solution is participating. It is revealed fo r 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 solu tion is applied onto the mica surface. (C) 2001 Published by Elsevier Scien ce B.V.