Slow Electron Spin Relaxation at Ambient Temperatures with Copper Coordinated by a Rigid Macrocyclic Ligand

Espinosa, Matthew R.; Guerrero, Fernando; Kazmierczak, Nathanael P.; Oyala, Paul H.; Hong, Alexandria; Hadt, Ryan G.; Agapie, Theodor

doi:10.1021/jacs.5c00803

Title: Slow Electron Spin Relaxation at Ambient Temperatures with Copper Coordinated by a Rigid Macrocyclic Ligand

Journal Article · 17 April 2025 · Journal of the American Chemical Society

DOI: https://doi.org/10.1021/jacs.5c00803 · OSTI ID:2560487

Espinosa, Matthew R. ^[1];

^[1];

^[1]; Hong, Alexandria ^[1];

^[1];

^[1]

California Institute of Technology (CalTech), Pasadena, CA (United States)

Paramagnetic transition metal complexes can serve as quantum bits, storing phase information through unpaired electrons. Despite their promise, these systems often require low temperatures and tend to rapidly decohere. Recent efforts have sought to improve longitudinal relaxation (T₁), which provides an upper limit for phase coherence (T_m), by investigating existing literature compounds with reduced vibrational coupling and orbital angular momentum. However, synthetic strategies for improving T₁ through novel ligand design have remained scant. Here, we disclose the synthesis of a new modular macrocyclic ligand framework with four nitrogen donors (N₄) derived from phenanthroline that supports room-temperature coherent Cu(II) spin centers. The optimized complex more than doubles the T₁ over the next best Cu(II)-N₄ compound and exhibits a room temperature coherence time (T_m) of 0.28 μs, close to previously reported values. This performance enhancement arises from a tight binding site with short Cu–N distances, resulting in a stronger ligand field and reduced thermal accessibility of symmetric vibrational modes. This work demonstrates a practical approach to enabling spin coherence at room temperature, a factor critical to accessing relevant quantum bits and biological sensors, through a designer macrocyclic ligand platform.

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Research Organization:: California Institute of Technology (CalTech), Pasadena, CA (United States)

Sponsoring Organization:: National Science Foundation (NSF); USDOE Office of Science (SC), Basic Energy Sciences (BES)

Grant/Contract Number:: SC0022089

OSTI ID:: 2560487

Journal Information:: Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 17 Vol. 147; ISSN 0002-7863

Publisher:: American Chemical Society (ACS)Copyright Statement

Country of Publication:: United States

Language:: English

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Title: Slow Electron Spin Relaxation at Ambient Temperatures with Copper Coordinated by a Rigid Macrocyclic Ligand

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