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Eggeling A, Ngendahimana T, Jeschke G, Eaton GR, Eaton SS. Exploring tunneling ESEEM beyond methyl groups in nitroxides at low temperatures. Phys Chem Chem Phys 2024; 26:15240-15254. [PMID: 38751211 PMCID: PMC11135458 DOI: 10.1039/d4cp01212g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2024] [Accepted: 05/04/2024] [Indexed: 05/30/2024]
Abstract
Tunneling of methyl rotors coupled to an electron spin causes magnetic field independent electron spin echo envelope modulation (ESEEM) at low temperatures. For nitroxides containing alkyl substituents, we observe this effect as a contribution at the beginning of the Hahn echo decay signal occurring on a faster time scale than the matrix-induced decoherence. The tunneling ESEEM contribution includes information on the local environment of the methyl rotors, which manifests as a distribution of rotation barriers P(V3) when measuring the paramagnetic species in a glassy matrix. Here, we investigate the differences in tunneling behaviour of geminal methyl and ethyl group rotors in nitroxides while exploring different levels of theory in our previously introduced methyl quantum rotor (MQR) model. Moreover, we extend the MQR model to analyze the tunneling ESEEM originating from two different rotor types coupled to the same electron spin. We find that ethyl groups in nitroxides give rise to stronger tunneling ESEEM contributions than methyl groups because the difference between hyperfine couplings of their methyl protons better matches the tunneling frequency. The methyl rotors of both ethyl and propyl groups exhibit distributions at lower rotation barriers compared to geminal methyl groups. This is in good agreement with density functional theory (DFT) calculations of their rotation barriers and showcases that conformational flexibility impacts the hindrance of rotation. Using Monte-Carlo based fitting in combination with an identifiability analysis of the MQR model parameter space, we extract rotation barrier distributions for the individual rotor types in mixed-rotor nitroxides as well as identify which rotors dominate the observed tunneling contribution in the Hahn echo decay signal.
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Affiliation(s)
- Andrea Eggeling
- ETH Zurich, Department of Chemistry and Applied Biosciences, Vladimir-Prelog-Weg 2, 8093 Zurich, Switzerland.
| | - Thacien Ngendahimana
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208, USA.
| | - Gunnar Jeschke
- ETH Zurich, Department of Chemistry and Applied Biosciences, Vladimir-Prelog-Weg 2, 8093 Zurich, Switzerland.
| | - Gareth R Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208, USA.
| | - Sandra S Eaton
- Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208, USA.
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Usevičius G, Turčak J, Zhang Y, Eggeling A, Einorytė Ž, Hope MA, Svirskas Š, Klose D, Kalendra V, Aidas K, Jeschke G, Banys J, Šimėnas M. Probing structural and dynamic properties of MAPbCl 3 hybrid perovskite using Mn 2+ EPR. Dalton Trans 2024; 53:7292-7302. [PMID: 38587489 PMCID: PMC11059044 DOI: 10.1039/d4dt00116h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2024] [Accepted: 04/02/2024] [Indexed: 04/09/2024]
Abstract
Hybrid methylammonium (MA) lead halide perovskites have emerged as materials exhibiting excellent photovoltaic performance related to their rich structural and dynamic properties. Here, we use multifrequency (X-, Q-, and W-band) electron paramagnetic resonance (EPR) spectroscopy of Mn2+ impurities in MAPbCl3 to probe the structural and dynamic properties of both the organic and inorganic sublattices of this compound. The temperature dependent continuous-wave (CW) EPR experiments reveal a sudden change of the Mn2+ spin Hamiltonian parameters at the phase transition to the ordered orthorhombic phase indicating its first-order character and significant slowing down of the MA cation reorientation. Pulsed EPR experiments are employed to measure the temperature dependences of the spin-lattice relaxation T1 and decoherence T2 times of the Mn2+ ions in the orthorhombic phase of MAPbCl3 revealing a coupling between the spin center and vibrations of the inorganic framework. Low-temperature electron spin echo envelope modulation (ESEEM) experiments of the protonated and deuterated MAPbCl3 analogues show the presence of quantum rotational tunneling of the ammonium groups, allowing to accurately probe their rotational energy landscape.
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Affiliation(s)
- Gediminas Usevičius
- Faculty of Physics, Vilnius University, Sauletekio 3, 10257 Vilnius, Lithuania.
| | - Justinas Turčak
- Faculty of Physics, Vilnius University, Sauletekio 3, 10257 Vilnius, Lithuania.
| | - Yuxuan Zhang
- Laboratory of Magnetic Resonance, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Andrea Eggeling
- Department of Chemistry and Applied Biosciences, ETH Zurich, Vladimir-Prelog-Weg 1-5/10, 8093 Zurich, Switzerland
| | - Žyginta Einorytė
- Faculty of Physics, Vilnius University, Sauletekio 3, 10257 Vilnius, Lithuania.
| | - Michael Allan Hope
- Laboratory of Magnetic Resonance, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Šarūnas Svirskas
- Faculty of Physics, Vilnius University, Sauletekio 3, 10257 Vilnius, Lithuania.
| | - Daniel Klose
- Department of Chemistry and Applied Biosciences, ETH Zurich, Vladimir-Prelog-Weg 1-5/10, 8093 Zurich, Switzerland
| | - Vidmantas Kalendra
- Faculty of Physics, Vilnius University, Sauletekio 3, 10257 Vilnius, Lithuania.
| | - Kestutis Aidas
- Faculty of Physics, Vilnius University, Sauletekio 3, 10257 Vilnius, Lithuania.
| | - Gunnar Jeschke
- Department of Chemistry and Applied Biosciences, ETH Zurich, Vladimir-Prelog-Weg 1-5/10, 8093 Zurich, Switzerland
| | - Jūras Banys
- Faculty of Physics, Vilnius University, Sauletekio 3, 10257 Vilnius, Lithuania.
| | - Mantas Šimėnas
- Faculty of Physics, Vilnius University, Sauletekio 3, 10257 Vilnius, Lithuania.
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Wakizaka M, Gupta S, Wan Q, Takaishi S, Noro H, Sato K, Yamashita M. Spin qubits of Cu(II) doped in Zn(II) metal-organic frameworks above microsecond phase memory time. Chemistry 2024; 30:e202304202. [PMID: 38146235 DOI: 10.1002/chem.202304202] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2023] [Accepted: 12/25/2023] [Indexed: 12/27/2023]
Abstract
With the aim of creating Cu(II) spin qubits in a rigid metal-organic framework (MOF), this work demonstrates a doping of 5 %, 2 %, 1 %, and 0.1 % mol of Cu(II) ions into a perovskite-type MOF [CH6 N3 ][ZnII (HCOO)3 ]. The presence of dopant Cu(II) sites are confirmed with anisotropic g-factors (gx =2.07, gy =2.12, and gz =2.44) in the S=1/2 system by experimentally and theoretically. Magnetic dynamics indicate the occurrence of a slow magnetic relaxation via the direct and Raman processes under an applied field, with a relaxation time (τ) of 3.5 ms (5 % Cu), 9.2 ms (2 % Cu), and 15 ms (1 % Cu) at 1.8 K. Furthermore, pulse-ESR spectroscopy reveals spin qubit properties with a spin-spin relaxation (phase memory) time (T2 ) of 0.21 μs (2 %Cu), 0.39 μs (1 %Cu), and 3.0 μs (0.1 %Cu) at 10 K as well as Rabi oscillation between MS =±1/2 spin sublevels. T2 above microsecond is achieved for the first time in the Cu(II)-doped MOFs. It can be observed at submicrosecond around 50 K. These spin relaxations are very sensitive to the magnetic dipole interactions relating with cross-relaxation between the Cu(II) sites and can be tuned by adjusting the dopant concentration.
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Affiliation(s)
- Masanori Wakizaka
- Department of Applied Chemistry and Bioscience, Faculty of Science and Technology, Chitose Institute of Science and Technology, 758-65 Bibi, Chitose, 066-8655, Japan
| | - Shraddha Gupta
- Department of Chemistry, Graduate School of Science, Tohoku University, 6-3 Aramaki-Aza-Aoba, Aoba-Ku, Sendai, 980-8578, Japan
| | - Qingyun Wan
- Department of Chemistry, State Key Laboratory of Synthetic Chemistry, HKU-CAS Joint Laboratory on New Materials, The University of Hong Kong
| | - Shinya Takaishi
- Department of Chemistry, Graduate School of Science, Tohoku University, 6-3 Aramaki-Aza-Aoba, Aoba-Ku, Sendai, 980-8578, Japan
| | - Honoka Noro
- Department of Chemistry, Graduate School of Science, Osaka Metropolitan University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka, 558-8585, Japan
| | - Kazunobu Sato
- Department of Chemistry, Graduate School of Science, Osaka Metropolitan University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka, 558-8585, Japan
| | - Masahiro Yamashita
- Department of Chemistry, Graduate School of Science, Tohoku University, 6-3 Aramaki-Aza-Aoba, Aoba-Ku, Sendai, 980-8578, Japan
- School of Chemical Science and Engineering, Tongji University, Siping Road 1239, Shanghai, 200092, P. R. China
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Perras FA, Matsuki Y, Southern SA, Dubroca T, Flesariu DF, Van Tol J, Constantinides CP, Koutentis PA. Mechanistic origins of methyl-driven Overhauser DNP. J Chem Phys 2023; 158:154201. [PMID: 37093991 DOI: 10.1063/5.0149664] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2023] [Accepted: 03/31/2023] [Indexed: 04/26/2023] Open
Abstract
The Overhauser effect in the dynamic nuclear polarization (DNP) of non-conducting solids has drawn much attention due to the potential for efficient high-field DNP as well as a general interest in the underlying principles that enable the Overhauser effect in small molecules. We recently reported the observation of 1H and 2H Overhauser effects in H3C- or D3C-functionalized Blatter radical analogs, which we presumed to be caused by methyl rotation. In this work, we look at the mechanism for methyl-driven Overhauser DNP in greater detail, considering methyl librations and tunneling in addition to classical rotation. We predict the temperature dependence of these mechanisms using density functional theory and spin dynamics simulations. Comparisons with results from ultralow-temperature magic angle spinning-DNP experiments revealed that cross-relaxation at temperatures above 60 K originates from both libration and rotation, while librations dominate at lower temperatures. Due to the zero-point vibrational nature of these motions, they are not quenched by very low temperatures, and methyl-driven Overhauser DNP is expected to increase in efficiency down to 0 K, predominantly due to increases in nuclear relaxation times.
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Affiliation(s)
- Frédéric A Perras
- Chemical and Biological Sciences Division, Ames National Laboratory, Ames, Iowa 50011, USA
- Department of Chemistry, Iowa State University, Ames, Iowa 50011, USA
| | - Yoh Matsuki
- Department of Chemistry, Iowa State University, Ames, Iowa 50011, USA
- Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan
| | - Scott A Southern
- Chemical and Biological Sciences Division, Ames National Laboratory, Ames, Iowa 50011, USA
| | - Thierry Dubroca
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA
| | - Dragos F Flesariu
- Department of Chemistry, University of Cyprus, P.O. Box 20537, 1678 Nicosia, Cyprus
| | - Johan Van Tol
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA
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