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Illuminating Ligand Field Contributions to Molecular Qubit Spin Relaxation via T₁ Anisotropy

Kazmierczak, Nathanael P. and Hadt, Ryan G. (2022) Illuminating Ligand Field Contributions to Molecular Qubit Spin Relaxation via T₁ Anisotropy. Journal of the American Chemical Society, 144 (45). pp. 20804-20814. ISSN 0002-7863. doi:10.1021/jacs.2c08729.

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Electron spin relaxation in paramagnetic transition metal complexes constitutes a key limitation on the growth of molecular quantum information science. However, there exist very few experimental observables for probing spin relaxation mechanisms, leading to a proliferation of inconsistent theoretical models. Here we demonstrate that spin relaxation anisotropy in pulsed electron paramagnetic resonance is a powerful spectroscopic probe for molecular spin dynamics across a library of highly coherent Cu(II) and V(IV) complexes. Neither the static spin Hamiltonian anisotropy nor contemporary computational models of spin relaxation are able to account for the experimental T1 anisotropy. Through analysis of the spin–orbit coupled wave functions, we derive an analytical theory for the T₁ anisotropy that accurately reproduces the average experimental anisotropy of 2.5. Furthermore, compound-by-compound deviations from the average anisotropy provide a promising approach for observing specific ligand field and vibronic excited state coupling effects on spin relaxation. Finally, we present a simple density functional theory workflow for computationally predicting T₁ anisotropy. Analysis of spin relaxation anisotropy leads to deeper fundamental understanding of spin–phonon coupling and relaxation mechanisms, promising to complement temperature-dependent relaxation rates as a key metric for understanding molecular spin qubits.

Item Type:Article
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URLURL TypeDescription
Kazmierczak, Nathanael P.0000-0002-7822-6769
Hadt, Ryan G.0000-0001-6026-1358
Additional Information:The authors would like to acknowledge Paul H. Oyala for assistance with EPR data collection, Ruben Mirzoyan and Jinsoo Park for discussions about spin relaxation theory, Ryan D. Ribson for providing the CuPc and VOPc samples, and Alexandra T. Barth for providing the [Cu(mnt)2]2– sample. N.P.K. acknowledges support by the Hertz Fellowship and the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1745301. The computations presented here were conducted in the Resnick High Performance Computing Center, a facility supported by Resnick Sustainability Institute at the California Institute of Technology. Financial support from the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Atomic, Molecular, and Optical Sciences program (DE-SC0022920), as well as Caltech and the Dow Next Generation Educator Fund, is gratefully acknowledged.
Group:Resnick Sustainability Institute
Funding AgencyGrant Number
Fannie and John Hertz FoundationUNSPECIFIED
NSF Graduate Research FellowshipDGE-1745301
Department of Energy (DOE)DE-SC0022920
Dow Next Generation Educator FundUNSPECIFIED
Issue or Number:45
Record Number:CaltechAUTHORS:20221128-494241100.49
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:118087
Deposited By: Research Services Depository
Deposited On:21 Dec 2022 17:50
Last Modified:21 Dec 2022 17:50

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