Hourglass nanographenes unlock strong, robust multi-spin entanglement

Researchers from the National University of Singapore (NUS) and collaborators have developed a predictive design strategy for creating graphene-like molecules with multiple interacting spins and enhanced resilience to magnetic perturbations, opening new avenues for molecular-scale quantum information technologies and next-generation spintronics.

The research team was led by Professor LU Jiong from the NUS Department of Chemistry and the NUS Institute for Functional Intelligent Materials, together with Professor WU Jishan from the NUS Department of Chemistry, and international collaborators, including key contributor Professor Pavel Jelínek from the Czech Academy of Sciences in Prague.

Magnetic nanographenes, which are molecules composed of fused benzene rings, are of growing interest for quantum technologies because they can host unpaired electrons, or spins, that may be used to store and process information. Unlike conventional magnetic materials based on metal atoms, these carbon-based systems offer chemical versatility and long spin coherence times. However, engineering a single molecule that contains multiple strongly coupled spins in a stable and controlled manner remains a major challenge.

A new design strategy

Building on a well-known molecular structure called “Clar’s goblet”, the research team synthesised two extended nanographenes, C₆₂H₂₂ and C₇₆H₂₆, using atomically precise on-surface chemistry, with their structures and properties characterised by scanning probe microscopy. By changing the molecular shape in two different ways, through lateral and vertical extension, the researchers were able to independently control both electron–electron interactions and the number of zero-energy modes. Although both molecules host four unpaired spins, these arise from distinct mechanisms. In one molecule, the spins are driven entirely by the geometry of the carbon framework. In the other, they result from a combination of geometric effects and enhanced interactions between electrons.

The research breakthrough was published in the journal Nature Synthesis on 21 April 2026.

Prof Lu said, “Our work establishes a clear structure–property relationship in hourglass-shaped nanographenes through combined experimental and theoretical investigations. These advances offer unprecedented control over the magnetic properties of molecular materials, opening new possibilities for molecular qubits and quantum simulators based on carbon platforms.”

Enhanced magnetic resilience

The research team also compared the magnetic resilience of the two tetraradical molecules using scanning probe microscopy measurements with a magnetic sensor. Although both molecules contain four strongly correlated spins, they behaved differently under external magnetic perturbations. One molecule showed much stronger resilience, meaning its quantum state was harder to disrupt during measurement. This robustness is especially important for applications such as molecular qubits, where preserving fragile quantum states is essential.

“Looking ahead, we aim to probe spin dynamics and coherence times at the single-molecule level, and to achieve coherent control of these entangled spins. This marks an important step towards the development of molecular qubits and spintronic nanodevices,” added Prof Lu.