TY - JOUR

T1 - The Quantum Dynamical Basis of a Classical Kinetic Scheme Describing Coherent and Incoherent Regimes of Radical Pair Recombination

AU - Lukzen, Nikita N.

AU - Klein, Johannes H.

AU - Lambert, Christoph

AU - Steiner, Ulrich E.

N1 - Publisher Copyright: © 2017 Walter de Gruyter GmbH, Berlin/Boston 2017.

PY - 2017/2/1

Y1 - 2017/2/1

N2 - In recent work from this group (J. H. Klein et al. J. Am. Chem. Soc. 2015, 137, 11011), the magnetic field dependent charge recombination kinetics in donor/Ir-complex/acceptor triads has been determined with outstanding accuracy and reproducibility. The field-dependent kinetics has been analyzed in terms of a classical reaction scheme including the field-independent rate parameters of singlet recombination (rate constant kS) and S/T0 mixing (rate constant kST0) and the field-dependent rate constant k±(B) connecting central and outer Zeeman levels. In the present work, the extraction of k± from the experimental data is more precisely defined and the appearance of a "coherent" and "incoherent" regime of spin motion in a double log plot of k± vs. B is confirmed. The experimental decay curves have been reproduced by a full quantum dynamical model based on the stochastic Liouville equation, which was solved numerically, taking into account isotropic hyperfine coupling with five nuclear spins (1 N on donor radical, 4 H on acceptor radical) and anisotropic hyperfine coupling with the nitrogen nucleus at the donor radical. The results of the quantum calculations serve as a rigorous basis of interpreting the classical parameter k±. Furthermore, it is demonstrated that the incoherent part of spin motion is essential for a full understanding of the charge recombination kinetics even in the "coherent" regime.

AB - In recent work from this group (J. H. Klein et al. J. Am. Chem. Soc. 2015, 137, 11011), the magnetic field dependent charge recombination kinetics in donor/Ir-complex/acceptor triads has been determined with outstanding accuracy and reproducibility. The field-dependent kinetics has been analyzed in terms of a classical reaction scheme including the field-independent rate parameters of singlet recombination (rate constant kS) and S/T0 mixing (rate constant kST0) and the field-dependent rate constant k±(B) connecting central and outer Zeeman levels. In the present work, the extraction of k± from the experimental data is more precisely defined and the appearance of a "coherent" and "incoherent" regime of spin motion in a double log plot of k± vs. B is confirmed. The experimental decay curves have been reproduced by a full quantum dynamical model based on the stochastic Liouville equation, which was solved numerically, taking into account isotropic hyperfine coupling with five nuclear spins (1 N on donor radical, 4 H on acceptor radical) and anisotropic hyperfine coupling with the nitrogen nucleus at the donor radical. The results of the quantum calculations serve as a rigorous basis of interpreting the classical parameter k±. Furthermore, it is demonstrated that the incoherent part of spin motion is essential for a full understanding of the charge recombination kinetics even in the "coherent" regime.

KW - charge recombination

KW - linked radical pairs

KW - spin chemistry

KW - spin relaxation

UR - http://www.scopus.com/inward/record.url?scp=85012196178&partnerID=8YFLogxK

U2 - 10.1515/zpch-2016-0833

DO - 10.1515/zpch-2016-0833

M3 - Article

AN - SCOPUS:85012196178

VL - 231

SP - 197

EP - 223

JO - Zeitschrift fur Physikalische Chemie

JF - Zeitschrift fur Physikalische Chemie

SN - 0942-9352

IS - 2

ER -