Analysis of Molecular Orientation within Self-Organized Dye Particles with Near-Field and Polarized Evanescent-Field Excited Fluorescence

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Typical one- or two-dimensional registration was observed in organic dye particles of micrometer and submicrometer size that were formed as precipitates on an ozone-treated hydrophilic glass surface when the organic solvent evaporated from a thin film of specimen solution at a precisely controlled evaporation rate. We successfully identified near-field-excited near-field fluorescence from single particles within these self-organized particle arrays. However, some of the particles, especially most of the small particles with diameters around 2 μm or less, did not show fluorescence under near-field observation. In contrast, far-field fluorescence, when excited by a polarized evanescent field, was observed, with its intensity depending on the excitation polarization, indicating that molecules' transition moment within dye particles orient parallel to the substrate surface. These two observations suggest that the near-field at the tip of the probe was polarized parallel to the probe axis. Another observation, that molecules seemed to orient in a similar direction among neighboring 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.
Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physicsの論文
2006-01-15