Supramolecular rosette intermediated homochiral double helix.

Precise organization of organic molecules into homochiral double-helix remains a challenge due to the difficulty in controlling both self-assembly process and chirality transfer across length scales. Here, we report that a type of bisnaphthalene bisurea molecule could assemble into chirality-controlled nanoscale double-helices by a supramolecular rosette-intermediated hierarchical self-assembly mechanism. A solvent-mixing self-assembly protocol is adopted to direct bisnaphthalene bisurea cyclization into chiral discrete rosettes through cooperative intramolecular and intermolecular hydrogen bonds. Controlled hexagonal packing of rosettes at higher concentrations gives one-dimensional single-stranded nanofibers, which intertwine into well-defined double-helix nanostructures with preferred chirality that depends on the absolute configurations of bisnaphthalene bisurea. The hierarchical organization of bisnaphthalene bisurea molecules enables effective excitation energy delocalization within the double-helix, which contributes to near-unity energy transfer from double-helix to adsorbed acceptor dyes even in donor/acceptor ratios over 1000, leading to bright circularly polarized luminescence from the originally achiral acceptor. The experimental and theoretical simulation results not only provide a hierarchical strategy to fabricate homochiral double-helix but also bring insights in understanding the high-efficiency light-harvesting process in photosystem II.