The layered structures of graphite and related nanographene molecules play a key role in their physical and electronic properties . The well-ordered molecular alignment of nanographenes and its structural determination are of interest in order to gain insight into a variety of carbon materials. It is well known that the one-dimensional (1D) assembly of planar nanographenes (e.g. hexa-peri-hexabenzocoronene) can be achieved by introducing suitable peripheral substituents that tune solubility (Figure ) . The 1D assembly of bowl-shaped nanographenes was also achieved by convex-concave π-π stacking along with non-covalent interactions . However, the stacking modes of negatively curved nanographenes remains unclear, owing to the lack of suitable nanographene molecules. In 2013, our group reported warped nanographene (WNG), a large nonplanar nanographene containing five seven-membered rings (Figure ) . In spite of its large structure with 80 carbon atoms (C80H30), WNG is soluble in various organic solvents because its negative curvature hinders π-π stacking. During related works on WNGs , we found that a synthetic intermediate of WNG (1-biph) efficiently forms stacked π-π dimers in the crystalline state . Considering the high solubility of the WNG family and the existence of a ππ stacking mode, we hypothesized that substituent-free 1D assemblies could be realized by using negatively curved nanographenes (Figure ). Herein, we report the synthesis and 1D self-assembly of a newly designed nanographene 1-H (C68H28), a negatively curved PAH with 12 carbon atoms fewer than WNG (Figure ). Serendipitously, we discovered that 1-H self-assembles in various organic solvents and works as a highly efficient gelator that forms organic gels at concentrations of <1 wt%. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) measurements confirm that 1-H forms fibers with diameters of ~2.8 nm. The presence of efficient π-π interactions in the fiber structures is supported by a bathochromic shift in the fluorescence spectrum of the gel state relative to that of dilute solutions of 1-H. Finally, using three-dimensional (3D) electron crystallography, the double-helix π-π stacking mode of 1-H in the supramolecular nanofiber was revealed.