Avoiding Bias Effects in NMR Experiments for Heteronuclear Dipole–Dipole Coupling Determinations: Principles and Application to Organic Semiconductor Materials

Authors

  • Ricardo Kurz,

    1. Institut für Physik-NMR, Martin-Luther-Universität Halle-Wittenberg, Betty-Heimann-Str. 7, 06120 Halle (Germany)
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  • Marcio Fernando Cobo,

    1. Instituto de Física de São Carlos, Universidade de São Paulo, Caixa Postal 369, CEP, 13560-970 São Carlos, São Paulo (Brasil)
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  • Prof. Dr. Eduardo Ribeiro de Azevedo,

    1. Instituto de Física de São Carlos, Universidade de São Paulo, Caixa Postal 369, CEP, 13560-970 São Carlos, São Paulo (Brasil)
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  • Dr. Michael Sommer,

    1. Angewandte Funktionspolymere, Makromolekulare Chemie I, Universität Bayreuth, 95440 Bayreuth (Germany)
    2. Institut für Makromolekulare Chemie, Albert-Ludwigs-Universität, 79100 Freiburg (Germany)
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  • Dr. André Wicklein,

    1. Angewandte Funktionspolymere, Makromolekulare Chemie I, Universität Bayreuth, 95440 Bayreuth (Germany)
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  • Prof. Dr. Mukundan Thelakkat,

    1. Angewandte Funktionspolymere, Makromolekulare Chemie I, Universität Bayreuth, 95440 Bayreuth (Germany)
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  • Dr. Günter Hempel,

    1. Institut für Physik-NMR, Martin-Luther-Universität Halle-Wittenberg, Betty-Heimann-Str. 7, 06120 Halle (Germany)
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  • Prof. Dr. Kay Saalwächter

    Corresponding author
    1. Institut für Physik-NMR, Martin-Luther-Universität Halle-Wittenberg, Betty-Heimann-Str. 7, 06120 Halle (Germany)
    • Institut für Physik-NMR, Martin-Luther-Universität Halle-Wittenberg, Betty-Heimann-Str. 7, 06120 Halle (Germany)

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Abstract

Carbon–proton dipole–dipole couplings between bonded atoms represent a popular probe of molecular dynamics in soft materials or biomolecules. Their site-resolved determination, for example, by using the popular DIPSHIFT experiment, can be challenged by spectral overlap with nonbonded carbon atoms. The problem can be solved by using very short cross-polarization (CP) contact times, however, the measured modulation curves then deviate strongly from the theoretically predicted shape, which is caused by the dependence of the CP efficiency on the orientation of the CH vector, leading to an anisotropic magnetization distribution even for isotropic samples. Herein, we present a detailed demonstration and explanation of this problem, as well as providing a solution. We combine DIPSHIFT experiments with the rotor-directed exchange of orientations (RODEO) method, and modifications of it, to redistribute the magnetization and obtain undistorted modulation curves. Our strategy is general in that it can also be applied to other types of experiments for heteronuclear dipole–dipole coupling determinations that rely on dipolar polarization transfer. It is demonstrated with perylene-bisimide-based organic semiconductor materials, as an example, in which measurements of dynamic order parameters reveal correlations of the molecular dynamics with the phase structure and functional properties.

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