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Assembling molecular Sierpiński triangle fractals

Nature Chemistry 7, 389–393 (2015) | Download Citation

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Abstract

Fractals, being “exactly the same at every scale or nearly the same at different scales” as defined by Benoit B. Mandelbrot, are complicated yet fascinating patterns that are important in aesthetics, mathematics, science and engineering. Extended molecular fractals formed by the self-assembly of small-molecule components have long been pursued but, to the best of our knowledge, not achieved. To tackle this challenge we designed and made two aromatic bromo compounds (4,4″-dibromo-1,1′:3′,1″-terphenyl and 4,4‴-dibromo-1,1′:3′,1″:4″,1‴-quaterphenyl) to serve as building blocks. The formation of synergistic halogen and hydrogen bonds between these molecules is the driving force to assemble successfully a whole series of defect-free molecular fractals, specifically Sierpiński triangles, on a Ag(111) surface below 80 K. Several critical points that govern the preparation of the molecular Sierpiński triangles were scrutinized experimentally and revealed explicitly. This new strategy may be applied to prepare and explore various planar molecular fractals at surfaces.

  • Compound C18H12Br2

    4,4''-dibromo-1,1':3',1''-terphenyl

  • Compound C24H16Br2

    4,4'''-dibromo-1,1':3',1'':4'',1'''-quaterphenyl

  • Compound C30H20Br2

    4,4''''-dibromo-1,1':4',1'':3'',1''':4''',1''''-quinquephenyl

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Acknowledgements

This work was jointly supported by National Natural Science Foundation of China (51121091, 21133001, 21333001, 21261130090, 61321001, 913000002) and Ministry of Science and Technology (2011CB808702, 2013CB933404), China, with partial support from the Singapore National Research Foundation CREATE-SPURc. We thank X. Ma at the School of Mathematics in Peking University for his assistance and discussions on the fractal structure analysis.

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Affiliations

  1. SKLSCUSS, BNLMS, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China

    • Jian Shang
    • , Jingxin Dai
    • , Xiong Zhou
    •  & Kai Wu

  2. Key Laboratory for the Physics and Chemistry of Nanodevices, Department of Electronics, Peking University, Beijing 100871, China

    • Yongfeng Wang

  3. Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Strasse, Marburg 35032, Germany

    • Min Chen
    • , Julian Kuttner
    • , Gerhard Hilt
    •  & J. Michael Gottfried

  4. Department of Chemical Physics, School of Chemistry and Materials Science, University of Science and Technology of China, Hefei 230026, China

    • Xiang Shao

  5. SPURc, 1 CREATE Way, #15-01, CREATE Tower, Singapore 138602, Singapore

    • Kai Wu

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Contributions

J.S., Y.F.W., J.M.G. and K.W. designed the experiments. J.S., M.C., J.X.D. and X.Z. performed the experiments. J.K. and G.H. synthesized the precursors. J.S., Y.F.W., X.S. and K.W. analysed the data and wrote the manuscript. All the authors discussed the results and commented on the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Yongfeng Wang or J. Michael Gottfried or Kai Wu.

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https://doi.org/10.1038/nchem.2211

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