Micrometer-sized rings self-assembled from thiacyanine dye molecules and their waveguiding properties

To fabricate ring-shaped waveguides on a micrometer scale, chloroform solutions of thiacyanine (TC) dyes having alkyl groups of different chain lengths ranging from -C2H5 to -C8H17 were drop-cast on a glass substrate and were allowed to evaporate under different conditions. It was found that the TC dyes with -C8H17 groups (TC8) self-assembled into well-defined rings with diameters of 5-30 mu m on evaporating the solution under highly humid conditions (relative humidity: -90%). The morphological and optical properties of the individual rings were investigated by microscopy techniques. The polarized fluorescence microscope image of the rings showed pronounced polarization effects, indicating that the molecules inside the rings are highly ordered. The mechanism of ring formation was discussed on the basis of the molecular arrangement within the rings. Furthermore, the waveguiding properties of the rings were investigated by spatially resolved fluorescence microscopy. It was found that the TC8 rings guided their fluorescence along the rings.