Optically Active Chiral CuO Nanoflowers

Helical symmetry can be found in most flowers with a rotation of contort petal aestivation. For micro- and nanoscale analogies, flower mimicking structures have been reproduced; however, the conceptual chirality of nanoflowers has not yet been defined. Here, the chirality of the flower was defined by its nanosized chiral structure and consequent optical activity (OA), opening new horizons for the physical theory and chiral materials. We report the surfactant-mediated hydrothermal synthesis of chiral CuO nanoflowers using sodium dodecyl sulfate (SDS) as a structure-directing agent, an amino alcohol as a symmetry-breaking agent, and cupric salt as the inorganic source. Two levels of hierarchical chirality exist for a CuO nanoflower including primary helically arranged nanoflakes and secondary helical subnanopetals that form nanopetals. The nanoflowers exhibited a prominent optical response to circularly polarized light (CPL) at the absorption bands characteristic of CuO.