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arXiv · 2610.24925

Symmetry-breaking chelation enables room-temperature all-optical spin coherence readout of aqueous Cu(II) for chemoselective discrimination

Jinlei Li·Qiaoyun Wu·Qiaoqiao Shao·Zhubin Hu·Haitao Sun·Zhenrong Sun·Donghai Feng
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Abstract

Optical initialization and readout of molecular electron spins in water remains challenging for 3d transition-metal complexes. Their Laporte-forbidden d-d transitions yield weak transition dipole moments, so optical spin detection in aqueous Cu(II) previously required ~1 M concentrations. Here we overcome this constraint through symmetry-breaking chelation. Coordinating Cu(II) with EDTA imposes a non-centrosymmetric ligand field with enhanced metal-ligand covalency, relaxing Laporte restrictions and amplifying d-d transition dipole moments. This design enhances absorption and magnetic circular dichroism by 7.3- and 5.6-fold, enabling ultrafast spin readout down to 100 μM with an apparent dephasing time T2^*~0.54 ns. As a proof-of-concept for selective molecular-spin sensing, histidine addition extends T_2^* to ~0.8 ns in a concentration-dependent manner, whereas glycine produces no measurable effect. These results show that symmetry breaking provides a strategy to create molecular spin-photon interfaces, opening avenues toward all-optical, analyte-responsive quantum sensing in water.

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Jinlei Li, Qiaoyun Wu, Qiaoqiao Shao, Zhubin Hu, Haitao Sun, Zhenrong Sun, Donghai Feng. 2026-10-18. Symmetry-breaking chelation enables room-temperature all-optical spin coherence readout of aqueous Cu(II) for chemoselective discrimination. https://arxiv.org/abs/2610.24925

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