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Application of optical nuclear polarization enhanced C-13 NMR

Buntkowsky, G. and Hoffmann, W. and Kupka, T. and Pasterna, G. and Jaworska, M. and Vieth, H. M. (1998):
Application of optical nuclear polarization enhanced C-13 NMR.
102, In: Journal of Physical Chemistry A, (29), pp. 5794-5801, [Online-Edition: http://apps.webofknowledge.com/full_record.do?product=WOS&se...],
[Article]

Abstract

A gain in detection sensitivity of more than 3 orders of magnitude has been achieved in high-resolution solid-state C-13 NMR of monocrystalline fluorene doped with acridine by applying optical nuclear polarization (ONP) via excited triplet states to protons and transferring this proton polarization to the C-13 nuclei. This sensitivity gain was utilized to measure the angular dependence (rotation pattern) of the C-13 NMR lines. In this way the principal values and orientations of all C-13 chemical shielding tensors were determined. While the C-13 shielding tensor of the bridging methylene group exhibits only a small anisotropy, at the aromatic carbon positions the typical strong anisotropy is observed. All tensors belonging to the same molecule have one principal axis, perpendicular to the molecular plane, in common, showing that in the crystal lattice the fluorene molecule is in a planar configuration. The experimental data are compared to ab initio calculations employing optimized geometries and gauge included atomic orbitals density functional theory (GIAO DFT). The orientations of all calculated tensors are in excellent agreement with the experimental data. On an absolute scale the calculated shielding parameters reproduce the experimental values reasonably well. A significant improvement of the calculated eigenvalues is achieved by shifting the tensors employing data from calculations of benzene and methane.

Item Type: Article
Erschienen: 1998
Creators: Buntkowsky, G. and Hoffmann, W. and Kupka, T. and Pasterna, G. and Jaworska, M. and Vieth, H. M.
Title: Application of optical nuclear polarization enhanced C-13 NMR
Language: English
Abstract:

A gain in detection sensitivity of more than 3 orders of magnitude has been achieved in high-resolution solid-state C-13 NMR of monocrystalline fluorene doped with acridine by applying optical nuclear polarization (ONP) via excited triplet states to protons and transferring this proton polarization to the C-13 nuclei. This sensitivity gain was utilized to measure the angular dependence (rotation pattern) of the C-13 NMR lines. In this way the principal values and orientations of all C-13 chemical shielding tensors were determined. While the C-13 shielding tensor of the bridging methylene group exhibits only a small anisotropy, at the aromatic carbon positions the typical strong anisotropy is observed. All tensors belonging to the same molecule have one principal axis, perpendicular to the molecular plane, in common, showing that in the crystal lattice the fluorene molecule is in a planar configuration. The experimental data are compared to ab initio calculations employing optimized geometries and gauge included atomic orbitals density functional theory (GIAO DFT). The orientations of all calculated tensors are in excellent agreement with the experimental data. On an absolute scale the calculated shielding parameters reproduce the experimental values reasonably well. A significant improvement of the calculated eigenvalues is achieved by shifting the tensors employing data from calculations of benzene and methane.

Journal or Publication Title: Journal of Physical Chemistry A
Volume: 102
Number: 29
Uncontrolled Keywords: magnetic shielding constants doped aromatic crystals radical pair formation localized quantities chemical-shifts excited-states fluorene onp susceptibilities optimization
Divisions: 07 Department of Chemistry
07 Department of Chemistry > Physical Chemistry
Date Deposited: 27 Oct 2014 20:37
Official URL: http://apps.webofknowledge.com/full_record.do?product=WOS&se...
Additional Information:

103HD Times Cited:19 Cited References Count:52

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