Towards Luminescent Vanadium(II) Complexes with Slow Magnetic Relaxation and Quantum Coherence

Molecular entities with doublet or triplet ground states find increasing interest as potential molecular quantum bits (qubits). Complexes with higher multiplicity might even function as qudits and serve to encode further quantum bits. Vanadium(II) ions in octahedral ligand fields with quartet ground...

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Published in:Chemistry : a European journal Vol. 29; no. 9; pp. e202202898 - n/a
Main Authors: Dorn, Matthias, Hunger, David, Förster, Christoph, Naumann, Robert, Slageren, Joris, Heinze, Katja
Format: Journal Article
Language:English
Published: Germany Wiley Subscription Services, Inc 10.02.2023
John Wiley and Sons Inc
Subjects:
Charge transfer
Chemistry
Coherence
Diamines
electron paramagnetic resonance
Energy gap
excited state order
Ground state
Isomers
Ligands
Magnetic induction
Magnetic relaxation
Quantum phenomena
Qubits (quantum computing)
spin-flip
Vanadium
magnetic relaxation
vanadium
excited state order
electron paramagnetic resonance
spin-flip
ISSN:0947-6539, 1521-3765, 1521-3765
Online Access:Get full text
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Summary:Molecular entities with doublet or triplet ground states find increasing interest as potential molecular quantum bits (qubits). Complexes with higher multiplicity might even function as qudits and serve to encode further quantum bits. Vanadium(II) ions in octahedral ligand fields with quartet ground states and small zero‐field splittings qualify as qubits with optical read out thanks to potentially luminescent spin‐flip states. We identified two V2+ complexes [V(ddpd)2]2+ with the strong field ligand N,N’‐dimethyl‐N,N’‐dipyridine‐2‐yl‐pyridine‐2,6‐diamine (ddpd) in two isomeric forms (cis‐fac and mer) as suitable candidates. The energy gaps between the two lowest Kramers doublets amount to 0.2 and 0.5 cm−1 allowing pulsed EPR experiments at conventional Q‐band frequencies (35 GHz). Both isomers possess spin‐lattice relaxation times T1 of around 300 μs and a phase memory time TM of around 1 μs at 5 K. Furthermore, the mer isomer displays slow magnetic relaxation in an applied field of 400 mT. While the vanadium(III) complexes [V(ddpd)2]3+ are emissive in the near‐IR‐II region, the [V(ddpd)2]2+ complexes are non‐luminescent due to metal‐to‐ligand charge transfer admixture to the spin‐flip states. Towards qubits with optical read‐out: Metal‐to‐ligand charge transfer (4MLCT) states account for the color of the vanadium(II) complex isomers cis‐fac‐ and mer‐[V(ddpd)2]2+ in spite of the electron‐rich pyridines. 2MLCT states mix with the lowest spin‐flip states, contracting the V−N bonds in the excited state and preventing ruby‐like spin‐flip emission. Both isomers possess spin‐lattice relaxation times of around 300 μs and a phase memory time of around 1 μs at 5 K.The mer isomer shows slow magnetic relaxation in an external magnetic field. These results pave the way for qubits with optical read‐out based on vanadium(II) complexes.
Bibliography:These authors contributed equally.
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ISSN:0947-6539
1521-3765
1521-3765
DOI:10.1002/chem.202202898