This work was supported by the ERATO programme from JST (JPMJER1302 to K.I.), the JSPS KAKENHI (grants JP26810057, JP16H00907, JP17K1955 and JP18H02019 to H.I.), the SUMITOMO Foundation (141495 to H.I.) and the DAIKO Foundation (H.I.). We acknowledge Taoka Chemical Co., Ltd for providing samples. We thank K. Kuwata (Nagoya University) for MALDI–TOF mass measurements; M. Kamigaito and M. Uchiyama (Nagoya University) for measurements of molecular weight by size-exclusion chromatography multi-angle light scattering (SEC-MALS); T. Hashizume (Hitachi Ltd and Tokyo Institute of Technology) for advice on the STM and AFM measurements; C. M. Crudden (Queen’s University and Nagoya University), G. J. P. Perry (Nagoya University) and A. Miyazaki (Nagoya University) for comments and proofreading. Computations were performed at the Research Center for Computational Science, Okazaki, Japan. ITbM is supported by the World Premier International Research Center (WPI) Initiative, Japan.

Reviewer information

Nature thanks Lawrence T. Scott and the other anonymous reviewer(s) for their contribution to the peer review of this work.