Micro rings self-assembled from organic NPB and their polarized optical properties

Micro rings of organic NPB have been prepared by evaporating chloroform solution on a silicon surface, which is assisted with a template of water droplets. The topography and optical properties of NPB rings were investigated by microscopy techniques. It is found that the polarized fluorescence microscope images of rings show pronounced polarization related to their central angle Φ. This indicates that the NPB molecules within a ring are ordered. Systematic investigation indicates that the water droplets condensed on silicon are essential for the ring formation. Such strategy is available for other small molecules, e.g., fullerene, porphyrin, and phthalocyanine.