Phase- and Shape-Controlled Synthesis of Single Crystalline Perylene Nanosheets and Its Optical Properties

Two-dimensional single-crystalline nanostructures of perylene with uniform square and rhombus shapes have been prepared successfully via a simple reprecipitation method with the assistance of surfactant CTAB templates. The X-ray diffraction (XRD) measurements reveal that the square and rhombus nanosheets can be indexed to alpha- and beta-phase perylene crystals, respectively. On the basis of the analysis of time-dependent growth processes, we found that selective adhesion of CTAB molecules on the crystal (001) plane facilitates to the formation of sheetlike structures, whereas polymorph transition from alpha- to beta-phase achieved by altering the surfactant CTAB concentration results in the evolution of the nanosheet from square to rhombus morphologies. Single-nanoparticle spectrscopy depicts that square and rhombus nanosheets show distinct shape-dependent optical properties that are directly related to their crystal structures. Furthermore, the optical waveguiding behaviors have been revealed through the scanning near-field optical microscopy (SNOM) technique. This expands the optical waveguides from 1D to 2D nanostructures and has a potential application in novel optoelectronic devices.