Crystallization-mediated twisting of supramolecular nanoribbons from plant-derived triterpenes

Controlling crystallization can tailor crystal properties, yet directing the supramolecular organization of small bio-based molecules remains challenging because of their configurational diversity and chemical complexity. Here, we direct the self-assembly of birch-bark-derived betulin (BT), a nonionic triterpene, into twisted supramolecular nanoribbons (BT_S). By interrupting classical nanolayer restacking and coupling interfacial dynamics with amphiphilic balance, surfactant- and salt-mediated antisolvent crystallization perturbs growth symmetry and biases directional molecular packing. The resulting twisted nanoribbons exhibit defined dimensions (width ~200 nm, thickness ~50 nm and ∼3.6 μm pitch) and aligned BT nanolayers with ~1.3 nm interlayer spacing. Polarization-resolved optical coherence tomography reveals depth-resolved mesoscale polarization anisotropy and links ribbon topology to effective refractive index and linear and circular birefringence. Molecular dynamics simulations support cooperative twisting driven by hydrophobic interactions and London dispersion forces. This crystallization-mediated strategy enables multiscale periodicity and tunable optical anisotropy, expanding opportunities for sustainable soft photonic and optoelectronic materials derived from biomolecules. Controlling the crystallization conditions allows to tailor the properties of crystals, but achieving directed supramolecular organization of small bio-based molecules remains challenging. Here the authors demonstrate direct supramolecular twisting and hierarchical organization in a triterpene system by directing the self-assembly of betulin into nanoribbons.