Spectroscopic and AFM studies on the structures of pseudoisocyanine J aggregates at a mica water interface

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, similar to 580 nm; line width (HWHM), similar to 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 similar to 10(6) 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 (similar to 50 ps) were unchanged. These results indicated that the physical aggregation size observed was much larger than the coherence size of the J aggregate.