Syngonanthus nitens: Why it looks like spun gold

• The paper explains why the stems of this crop display a golden shine.
• Flavonoids are shown to be responsible for the optical properties of the dried plant stems.
• We show theoretically and experimentally why flavonoids absorb in the UV.

We report on the optical properties of Syngonanthus nitens, the golden grass, which is used to produce golden handicraft articles. The dry stems of the plant were analyzed with scanning electron microscopy, X-ray photoelectron spectroscopy, fluorescence microscopy; angle resolved optical reflectance and absorption/emission spectroscopy. The extract of the stems composed by 8 glucopyranosylflavones was also optically characterized. Electronic and geometric properties of the flavonoids were studied using ab initio and semi-empirical quantum mechanical calculations. The experimental and theoretical results explain the characteristic golden color of S. nitens dried stems.