Molecular ordering in self-organized dye particles: polarized evanescent-field studies.

ABSTRACT

Self-organized rhodamine 6G particles prepared by wetting/dewetting process of an ethanol solution on a hydrophilic glass surface did show fluorescence without quenching. Polarized evanescent-field excitation showed that the molecule's transition moment within dye particles was oriented unidirectionally and parallel to the substrate surface. The deduced dye orientation showed correlation between adjacent particles, which implies a simultaneous aggregate growth from a common crystal seed grown in a possible 'arm' region connecting the adjacent droplets just before these droplets were disconnected upon solvent evaporation. The dye orientation of most particles pointed about 45 degrees off the dewetting direction. By contrast, the particles of another pi-conjugated NK1420 dye, J-aggregates of which grow easily from an oversaturated solution, showed dye orientation along the dewetting direction preferably, still indicating the effect of self-organization, however based on a different mechanism.