Abstract
Free radicals, generally formed through the cleavage of covalent electron-pair bonds, play an important role in diverse fields ranging from synthetic chemistry to spintronics and nonlinear optics. However, the characterization and regulation of the radical state at a single-molecule level face formidable challenges. Here we present the detection and sophisticated tuning of the open-shell character of individual diradicals with a donor–acceptor structure via a sensitive single-molecule electrical approach. The radical is sandwiched between nanogapped graphene electrodes via covalent amide bonds to construct stable graphene–molecule–graphene single-molecule junctions. We measure the electrical conductance as a function of temperature and track the evolution of the closed-shell and open-shell electronic structures in real time, the open-shell triplet state being stabilized with increasing temperature. Furthermore, we tune the spin states by external stimuli, such as electrical and magnetic fields, and extract thermodynamic and kinetic parameters of the transition between closed-shell and open-shell states. Our findings provide insights into the evolution of single-molecule radicals under external stimuli, which may proof instrumental for the development of functional quantum spin-based molecular devices.
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Data availability
The data supporting the findings of this study are available within the paper and Supplementary Information. The datasets used in Supplementary Information are available online from the Zenodo repository at https://zenodo.org/records/10603012. Source data are provided with this paper.
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Acknowledgements
The authors acknowledge primary financial support from the National Key R&D Program of China (2021YFA1200101 (to X.G.) and 2022YFA0128700 (to X.G.)), the National Natural Science Foundation of China (22150013 (to X.G.), 21727806 (to X.G.), 21933001(to X.G.), 22288201 (to X.L.), 22322304 (to X.L.), 22375065 (to Y.L.) and 51973063 (to Y.L.)), the Tencent Foundation through the XPLORER PRIZE (to X.G.), ‘Frontiers Science Center for New Organic Matter’ at Nankai University (63181206 (to X.G.)), the Natural Science Foundation of Beijing (2222009 (to X.G.)), the Tip-top Scientific and Technical Innovative Youth Talents of Guangdong Special Support Program (2019TQ05C890 (to Y.L.)) and the National Science Foundation (OIA-1757220 (to N.R.)).
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X.G., F.H. and Y.L. conceived the idea for the paper. C.Ya., J.C. and G.K. fabricated the devices and performed the device measurements. Z.C., W.Z., W.L., J.H. and W.C. carried out the molecular synthesis and characterization. C.S., M.A.S. and N.R. performed calculations for the analysis of the open-shell character and aromaticity. C.Yu., X.L. and J.Y. built and analysed the theoretical model and performed the quantum transport calculation. X.G., F.H., Y.L. and C.Ya. analysed the data and wrote the paper. All the authors discussed the results and commented on the manuscript.
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Nature Nanotechnology thanks Pascal Gehring, Weida Hu and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Yang, C., Chen, Z., Yu, C. et al. Regulation of quantum spin conversions in a single molecular radical. Nat. Nanotechnol. (2024). https://doi.org/10.1038/s41565-024-01632-2
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DOI: https://doi.org/10.1038/s41565-024-01632-2
