Molecular Ordering in Self-Organized Dye Particles--Near-Field and Polarized Evanescent-Field Fluorescence Study--

Shinji KINOSHITA
Akihiro TOMIOKA
Atsushi FUJIMOTO
Yasuaki ITAKURA

Publication
IEICE TRANSACTIONS on Electronics   Vol.E89-C    No.12    pp.1735-1740
Publication Date: 2006/12/01
Online ISSN: 1745-1353
DOI: 10.1093/ietele/e89-c.12.1735
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Towards the Realization of Organic Molecular Electronics)
Category: Evaluation of Organic Materials
Keyword: 
self assembled,  dewetting process,  pi conjugated dye,  near field,  evanescent field,  molecular orientation,  

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Summary: 
Self-organized organic dye particles of micrometer and submicrometer size were prepared by utilizing a wetting/dewetting process of polar solvent on a hydrophilic glass substrate. The near-field scanning optical microscopy successfully identified near-field excited near-field fluorescence from single particles, however, the majority 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 the intensity depending on the excitation polarization, indicating that molecules' transition moment within dye particles was oriented parallel to the substrate surface. Single particle fluorescence spectrum consistently showed an identical sharp peak with a large redshift, indicating that the particles were composed of identical dye aggregates similar to J-aggregates. 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 orientation among adjacent particles, which further proves that the present specimen was formed by a self-organizing mechanism.