Spectroscopic and AFM Studies on the Structures of Pseudoisocyanine<i>J</i>Aggregates at a Mica/Water Interface

Abstract

J aggregates of a pseudoisocyanine dye (PIC) at a mica/solution interface were in situ observed in solution for the first time by atomic force microscopy (AFM), confirming formation of the aggregates showing a narrow J absorption band (peak, ∼580 nm; line width (HWHM), ∼120−125 cm-1) at room temperature. The J aggregates possessed the three-dimensional island structure with the height of about 3−6 nm, consisting of at least ∼106 PIC molecules, but not a two-dimensional monolayer structure. The growth processes of the J aggregates were discussed on the basis of the morphological changes of the islands with a dye concentration (i.e., Volmer−Weber type growth process), while the optical properties such as the absorption peak position, line width, or fluorescence lifetime (∼50 ps) were unchanged. These results indicated that the physical aggregation size observed was much larger than the coherence size of the J aggregate.