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Quantum nanomagnets in on-surface metal-free porphyrin chains

Nature Chemistry volume 15, pages 53–60 (2023)Cite this article

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Abstract

Unlike classic spins, quantum magnets are spin systems that interact via the exchange interaction and exhibit collective quantum behaviours, such as fractional excitations. Molecular magnetism often stems from d/f-transition metals, but their spin–orbit coupling and crystal field induce a significant magnetic anisotropy, breaking the rotation symmetry of quantum spins. Thus, it is of great importance to build quantum nanomagnets in metal-free systems. Here we have synthesized individual quantum nanomagnets based on metal-free multi-porphyrin systems. Covalent chains of two to five porphyrins were first prepared on Au(111) under ultrahigh vacuum, and hydrogen atoms were then removed from selected carbons using the tip of a scanning tunnelling microscope. The conversion of specific porphyrin units to their radical or biradical state enabled the tuning of intra- and inter-porphyrin magnetic coupling. Characterization of the collective magnetic properties of the resulting chains showed that the constructed S = 1/2 antiferromagnets display a gapped excitation, whereas the S = 1 antiferromagnets exhibit distinct end states between even- and odd-numbered spin chains, consistent with Heisenberg model calculations.

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Fig. 1: Construction of molecular nanomagnets in metal-free porphyrins.
Fig. 2: Characterization of intra-unit magnetic coupling within porphyrin monomers.
Fig. 3: Characterization of inter-unit magnetic coupling within porphyrin dimers.
Fig. 4: Antiferromagnetic coupled finite S = 1/2 spin chain.
Fig. 5: Antiferromagnetic coupled finite S = 1 spin chains.

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Data availability

Data supporting the findings of this study are available within the paper and its Supplementary Information. The Supplementary Information includes details of experiments, synthetic procedures and characterization data of the molecular precursor, as well as details of calculations. Source data are provided with this paper.

Code availability

The Heisenberg Hamiltonians were solved using Python. Details of this code are available from the corresponding author on request.

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Acknowledgements

S.W. acknowledges financial support from the National Key R&D Program of China (no. 2020YFA0309000), the National Natural Science Foundation of China (nos. 11874258 and 12074247), the Shanghai Municipal Science and Technology Qi Ming Xing Project (no. 20QA1405100), Fok Ying Tung Foundation for young researchers and SJTU (no. 21×010200846). This work is also partially supported by the Ministry of Science and Technology of China (grants nos. 2019YFA0308600, 2016YFA0301003 and 2016YFA0300403), NSFC (grants nos. 11521404, 11634009, 92065201, 11874256, 11790313 and 11861161003), the Strategic Priority Research Program of Chinese Academy of Sciences (grant no. XDB28000000) and the Science and Technology Commission of Shanghai Municipality (grants nos. 2019SHZDZX01, 19JC1412701 and 20QA1405100). We acknowledge the π 2.0 cluster of the Center for High Performance Computing at Shanghai Jiao Tong University.

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Author notes

  1. These authors contributed equally: Yan Zhao, Kaiyue Jiang, Can Li.

Authors and Affiliations

  1. Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai, China

    Yan Zhao, Can Li, Yufeng Liu, Gucheng Zhu, Dandan Guan, Yaoyi Li, Hao Zheng, Canhua Liu, Jinfeng Jia, Mingpu Qin & Shiyong Wang

  2. The meso-Entropy Matter Lab, School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai, China

    Kaiyue Jiang & Xiaodong Zhuang

  3. School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA

    Michele Pizzochero & Efthimios Kaxiras

  4. Department of Physics, Harvard University, Cambridge, MA, USA

    Efthimios Kaxiras

  5. Tsung-Dao Lee Institute, Shanghai Jiao Tong University, Shanghai, China

    Dandan Guan, Yaoyi Li, Hao Zheng, Canhua Liu, Jinfeng Jia, Mingpu Qin & Shiyong Wang

  6. Shanghai Research Center for Quantum Sciences, Shanghai, China

    Dandan Guan, Yaoyi Li, Hao Zheng, Canhua Liu, Jinfeng Jia & Shiyong Wang

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Contributions

S.W. conceived the experiments. Y.Z., C. Li and G.Z. performed the SPM experiments. K.J. and X.Z. synthesized the molecular precursors. Y. Liu performed the DFT calculations in the gas phase. M.P. and E.K. performed the DFT calculations on Au(111). C. Li and M.Q. performed the modelling calculations. D.G., Y. Li, H.Z., C. Liu and J.J. analysed the STS data. S.W., Y.Z. and C. Li wrote the paper. All authors discussed the results and implications and commented on the manuscript at all stages.

Corresponding authors

Correspondence to Xiaodong Zhuang or Shiyong Wang.

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Nature Chemistry thanks Pavel Jelinek, Jiong Lu, Oleg Yazyev and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–22, molecular precursor synthesis details and calculation details.

Supplementary Data 1

Raw NMR data, unprocessed STM and AFM images, source dI/dV spectroscopic data and computational data for supplementary information.

Source data

Source Data Fig. 1

Unprocessed STM and AFM images.

Source Data Fig. 2

Unprocessed STM images, AFM images, source dI/dV spectra and DFT electronic geometries.

Source Data Fig. 3

Unprocessed STM images and source dI/dV spectra.

Source Data Fig. 4

Unprocessed STM images and source dI/dV spectra.

Source Data Fig. 5

Unprocessed STM images, AFM images, source dI/dV spectra and Heisenberg calculations.

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Zhao, Y., Jiang, K., Li, C. et al. Quantum nanomagnets in on-surface metal-free porphyrin chains. Nat. Chem. 15, 53–60 (2023). https://doi.org/10.1038/s41557-022-01061-5

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