The self-assembly of organic molecules into supramolecular materials with structural ordering beyond the nanometre scale is challenging. Here, we report the spontaneous self-assembly of a chiral discotic triphenylene derivative into millimetre-sized droplets. The structure of the droplets is characterized by high positional and orientational ordering and a three-dimensional integrity similar to that of single crystals. Notwithstanding, these assemblies slide when placed on a vertical substrate demonstrating their fluid nature. X-ray imaging shows that during the sliding process the internal crystal-like structure is maintained and that the droplets undergo clockwise or counterclockwise unidirectional rotation, depending on the chirality of their molecular components. Rheological measurements suggest that this rotational behaviour might result from the distinct yield stress between the (R)- and (S)-enantiomers. Overall, our findings demonstrate that molecular chirality can determine the movement direction of a supramolecular structure, thus expanding the fundamental understanding of the structure and dynamics of soft materials.
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Crystal data of (R)-2 is available from the Cambridge Crystallographic Data Centre (CCDC) under reference number 1824673. Any other data supporting the findings of this study are available within the article and its supplementary files and available from the authors upon reasonable request.
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This work was supported by a Grant-in-Aid for Scientific Research on Innovative Areas “π-Figuration” (26102008) from The Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan, and KAKENHI (17H01034) from the Japan Society for the Promotion of Science (JSPS). This work was also supported in part by “Dynamic Alliance for Open Innovation Bridging Human, Environment and Materials” from MEXT, Japan. The synchrotron XRD experiments were performed at the BL45XU beamline in the SPring-8 with the approval of the RIKEN SPring-8 Center (proposal numbers 20140056, 20150068, 20160027 and 20170055). We thank Y. Shinozaki (Anton Paar Japan) for his assistance with the dynamic viscoelasticity measurements of (R)-2. We are grateful to S.-i. Adachi and R. Kumai (High Energy Accelerator Research Organization) and G. Ungar and X. Zeng (The University of Sheffield) for very valuable discussions about structural characterization. The authors would also like to thank Suzukakedai Materials Analysis Division, Technical Department, Tokyo Institute of Technology, for their support with the NMR measurements.