Polychlorinated trityl radicals for dynamic nuclear polarization: the role of chlorine nuclei

Paniagua, Juan Carlos; Mugnaini, Verónica; Gabellieri, Cristina; Feliz, Miguel; Roques, Nans; Veciana, Jaume; Pons, Miquel

doi:10.1039/c003291n

Cited by 21 publications

(33 citation statements)

References 34 publications

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“…Moreover, it was suggested that strong mixing of the nuclear states by the 35,37 Cl nuclear quadrupole interaction could increase the transition probability of the forbidden EPR transitions enhancing the efficiency of solid effect DNP. Such an assumption was supported by Density Functional Theory (DFT) calculations that predicted large quadrupole coupling constants and non--negligible hyperfine couplings for the chlorine nuclei 14 . The proposed chlorine assisted polarization transfer could represent a new heteronuclear DNP enhancement mechanism with widespread possible applications in the field of both NMR and MRI.…”

Section: Introductionmentioning

confidence: 83%

“…The results obtained during earlier ex--situ DNP studies carried out with PTMs 14,15 , particularly the DNP frequency sweeps, suggested a chlorine--assisted polarization transfer mechanism for both radicals 1 and 2. Radical 1 was reported to produce solution 13 C signal enhancement comparable to the commercial DNP polarizer OX63 whereas radical 2 gave a much lower DNP enhancement.…”

Section: Introductionmentioning

confidence: 94%

“…This estimated DNP sweep is shown in Fig. 3 (dashed line) and compared with the experimental DNP sweep measured at 1.5 K using 15mM of radicals 1 or 2 in neat pyruvic acid 14,15 . In this calculation we did not take into account any spin relaxation mechanism and ignored any orientation dependence of forbidden EPR transition probabilities.…”

Section: Ghz Echo Detected Epr Spectra and Spin Lattice Relaxation Timesmentioning

confidence: 99%

“…One notable aspect of all the ELDOR--detected NMR spectra is the broad feature in the frequency range of 30--45 MHz which overlaps the 13 C Larmor frequency, ν 13C . The frequency match between some of the forbidden transitions involving chlorine nuclei and ν 13C at the magnetic field used in the DNP experiments can provide a mechanism for spin diffusion from the initially polarized 35,37 Cl nuclei to bulk 13 C nuclei, as originally suggested 14,15 . On the other hand, the broad spread of forbidden transitions originating from the quadrupolar nature of chlorine may allow efficient DNP to 35,37 Cl, and indirectly to 13 C, at a broad range of mw frequencies.…”

Section: Mapping the Forbidden Epr Transitionsmentioning

confidence: 99%

“…1, can also be used to polarize 13 C nuclei in ex--situ DNP experiments with a rather good efficiency 14,15 . These radicals consist of a triphenylmethyl skeleton, as in OX63, but while in the OX63 the central carbon atom is protected by six 5--membered rings containing sulphur ( Fig.…”

Section: Introductionmentioning

confidence: 99%

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Correlation of the EPR properties of perchlorotriphenylmethyl radicals and their efficiency as DNP polarizers

Banerjee

Paniagua

Mugnaini

et al. 2011

Phys. Chem. Chem. Phys.

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Water soluble perchlorinated trityl (PTM) radicals were found to be effective 95 GHz DNP (dynamic nuclear polarization) polarizers in ex--situ (dissolution) 13 C DNP (Gabellieri et al, Angew Chem. Int. Ed. 2010, 49, 3360). The degree of the nuclear polarization obtained was reported to depend on the position of the chlorine substituents on the trityl skeleton. In addiiton, on the basis of the DNP frequency sweeps it was suggested that the 13 C NMR signal enhancement is mediated by the Cl nuclei. To understand the DNP mechanism of the PTM radicals we have explored the 95 GHz EPR characteristics of these radicals that are relevant to their performance as DNP polarizers. The EPR spectra of the radicals revealed axially symmetric g--tensors. A comparison of the spectra with the 13 C DNP frequency sweeps showed that although the solid effect mechanism is operational the DNP frequency sweeps reveals some extra width suggesting that contributions from EPR forbidden transitions involving 35,37 Cl nuclear flips are likely. This was substantiated experimentally by ELDOR (electron--electron double resonance) detected NMR measurements, which map the EPR forbidden transitions, and ELDOR experiments that follow the depolarization of the electron spin upon irradiation of the forbidden EPR transitions.DFT (density functional theory) calculations helped to assign the observed transitions and provided the relevant spin Hamiltonian parameters. These results show that the 35,37 Cl hyperfine and nuclear quadrupolar interactions cause a considerable nuclear state mixing at 95 GHz thus facilitating the polarizing of the Cl nuclei upon microwave irradiation. Overlap of Cl nuclear frequencies and the 13 C Larmor frequency further facilitates the polarization of the 13 C nuclei by 2 spin diffusion. Calculation of the 13 C DNP frequency sweep based on the Cl nuclear polarization showed that it does lead to an increase in the width of the spectra, improving the agreement with the experimental sweeps, thus supporting the existence of the new heteronuclear assisted DNP mechanism.

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Section: Introductionmentioning

confidence: 83%

Section: Introductionmentioning

confidence: 94%

Section: Ghz Echo Detected Epr Spectra and Spin Lattice Relaxation Timesmentioning

confidence: 99%

Section: Mapping the Forbidden Epr Transitionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Correlation of the EPR properties of perchlorotriphenylmethyl radicals and their efficiency as DNP polarizers

Banerjee

Paniagua

Mugnaini

et al. 2011

Phys. Chem. Chem. Phys.

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View full text Add to dashboard Cite

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Molecular One‐ and Two‐Qubit Systems with Very Long Coherence Times

Schäfter,

Wischnat,

Tesi

et al. 2023

Advanced Materials

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General‐purpose quantum computation and quantum simulation require multi‐qubit architectures with precisely defined, robust interqubit interactions, coupled with local addressability. This is an unsolved challenge, primarily due to scalability issues. These issues often derive from poor control over interqubit interactions. Molecular systems are promising materials for the realization of large‐scale quantum architectures, due to their high degree of positionability and the possibility to precisely tailor interqubit interactions. The simplest quantum architecture is the two‐qubit system, with which quantum gate operations can be implemented. To be viable, a two‐qubit system must possess long coherence times, the interqubit interaction must be well defined and the two qubits must also be addressable individually within the same quantum manipulation sequence. Here results are presented on the investigation of the spin dynamics of chlorinated triphenylmethyl organic radicals, in particular the perchlorotriphenylmethyl (PTM) radical, a mono‐functionalized PTM, and a biradical PTM dimer. Extraordinarily long ensemble coherence times up to 148 µs are found at all temperatures below 100 K. Two‐qubit and, importantly, individual qubit addressability in the biradical system are demonstrated. These results underline the potential of molecular materials for the development of quantum architectures.

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Redox‐Addressable Single‐Molecule Junctions Incorporating a Persistent Organic Radical**

et al. 2022

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Integrating radical (open‐shell) species into non‐cryogenic nanodevices is key to unlocking the potential of molecular electronics. While many efforts have been devoted to this issue, in the absence of a chemical/electrochemical potential the open‐shell character is generally lost in contact with the metallic electrodes. Herein, single‐molecule devices incorporating a 6‐oxo‐verdazyl persistent radical have been fabricated using break‐junction techniques. The open‐shell character is retained at room temperature, and electrochemical gating permits in situ reduction to a closed‐shell anionic state in a single‐molecule transistor configuration. Furthermore, electronically driven rectification arises from bias‐dependent alignment of the open‐shell resonances. The integration of radical character, transistor‐like switching, and rectification in a single molecular component paves the way to further studies of the electronic, magnetic, and thermoelectric properties of open‐shell species.

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Polychlorinated trityl radicals for dynamic nuclear polarization: the role of chlorine nuclei

Cited by 21 publications

References 34 publications

Correlation of the EPR properties of perchlorotriphenylmethyl radicals and their efficiency as DNP polarizers

Correlation of the EPR properties of perchlorotriphenylmethyl radicals and their efficiency as DNP polarizers

Molecular One‐ and Two‐Qubit Systems with Very Long Coherence Times

Redox‐Addressable Single‐Molecule Junctions Incorporating a Persistent Organic Radical**

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