Double-Helix Supramolecular Nanofibers Assembled from Negatively Curved Nanographenes.

Kenta Kato,Yusuke Nakanishi,Yuh Hijikata,Yasutomo Segawa,Kiyofumi Takaba,Kenichiro Itami,Takuma Kawada,Saori Maki-Yonekura,Nobuhiko Mitoma,Koji Yonekura,Jenny Pirillo,Lawrence T Scott,Taishi Nishihara,Taito Hatakeyama

doi:10.1021/jacs.1c00863

Abstract

The layered structures of graphite and related nanographene molecules play key roles in their physical and electronic functions. However, the stacking modes of negatively curved nanographenes remain unclear, owing to the lack of suitable nanographene molecules. Herein, we report the synthesis and one-dimensional supramolecular self-assembly of negatively curved nanographenes without any assembly-assisting substituents. This curved nanographene self-assembles in various organic solvents and acts as an efficient gelator. The formation of nanofibers was confirmed by microscopic measurements, and an unprecedented double-helix assembly by continuous π-π stacking was uncovered by three-dimensional electron crystallography. This work not only reports the discovery of an all-sp2-carbon supramolecular π-organogelator with negative curvature but also demonstrates the power of three-dimensional electron crystallography for the structural determination of submicrometer-sized molecular alignment.

Highlights

The layered structures of graphite and related nanographene molecules play a key role in their physical and electronic properties (1–6)
To the best of our knowledge, there is no report of any unfunctionalized aromatic hydrocarbon that works as an organogelator (19–26). Intrigued by this unique behavior, we conducted a detailed investigation of the gelating ability of 1-H in various organic solvents (Figure 3C)
The pitch length of the helix is 3.1 nm, and 8 molecules constitute a helical repeat unit (Figure 4H). These findings clearly demonstrate the power of 3D electron crystallography for the structural determination of nanometer-sized molecular alignments, even for cases in which single crystals suitable for x-ray crystallography cannot be obtained

Summary

Main Text

The layered structures of graphite and related nanographene molecules play a key role in their physical and electronic properties (1–6). 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. 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 1B). 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 1C). To the best of our knowledge, there is no report of any unfunctionalized aromatic hydrocarbon that works as an organogelator (19–26) Intrigued by this unique behavior, we conducted a detailed investigation of the gelating ability of 1-H in various organic solvents (Figure 3C). This behavior stands in sharp contrast to the structurally similar derivative 1-Cl, which readily forms single crystals

Materials and Methods

Findings

Data processing and structure determination