Structural and Optical Controls of Mesoscopic Supramolecular Aggregates by the Function of an Interface of Two Phases

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The J aggregates of a pseudoisocyanine (PIC) dye were formed at a mica/aqueous solution interface and showed characteristic optical features. The J aggregates at various dye concentrations were in situ observed in solution by atomic force microscopy (AFM), and they were elucidated to possess three-dimensional domain island structures for the first time. Because the absorption peak wavelength, line width, or fluorescence lifetime was independent of the growth processes of the aggregates, the physical aggregation size (>〜10^6 molecules) is suggested to be much larger than the coherence size at room temperature.Aqueous mixed solutions of PIC and its structural analogous asymmetric cyanine (AC) dye formed amalgamated J aggregates at a mica/solution interface, and the formation mechanism of the aggregates was clarified by determining the optical, structural, and morphological properties of such aggregates. The florescence microscopy system constructed in our laboratory showed that the emissive amalgamated J aggregates possessed mesoscopic island domain morphology. The J aggregates covered the interface completely while the AC mole fraction was small. With increasing the AC mole fraction, the emissive J aggregate islands decreased in size and number and were discretely distributed, although AFM showed that the interface was still completely covered by adsorbed molecules. For the first time, our results show that dye adsorption from PIC/AC mixture solutions generated two types of island domain formation at the mica/solution interface (mesoscopic phase separation) : emissive amalgamated J aggregate island (PIC rich domain) and non-emissive island in the absence of J aggregates (AC-rich domain).