Self-Organized Arrays of Submicrometer Aggregates of π-Conjugated Dye and Its Near-Field Optical Study

Abstract

A wetting/dewetting process was utilized to prepare a self-organized formation of organic dye particles of micrometer and submicrometer size in one- or two-dimensional registration. The near-field scanning optical microcopy (NSOM) study successfully identified near-field-excited near-field fluorescence from single particles. The majority of small particles with diameters around 2 µm or less, however, did not show fluorescence under near-field observation. In contrast, far-field fluorescence, when excited by a polarized evanescent field, was observed, with the intensity depending on the excitation polarization. This indicates that molecule transition moment within dye particles was oriented parallel to the substrate surface. These observations suggest that the near-field at the probe tip was polarized parallel to the probe axis. Another observation, that molecules were oriented in a similar direction among adjacent particles, suggests that the dewetting process contributed to the alignment of the molecular direction among adjacent particles, which further proves that the present specimen was formed by a self-organizing mechanism.