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Investigation of structure and dynamics in a photochromic molecular crystal by NMR crystallography

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Investigation of structure and dynamics in a photochromic molecular crystal by NMR crystallography. / Dale, Benjamin L.; Halcovitch, Nathan R.; Peach, Michael J.G.; Griffin, John M.

In: Magnetic Resonance in Chemistry, Vol. 57, No. 5, 01.05.2019, p. 230-242.

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@article{86562293d76242648ffed62a8a285a6a,
title = "Investigation of structure and dynamics in a photochromic molecular crystal by NMR crystallography",
abstract = "A photochromic anil, N-(3,5-di-t-butylsalicylidene)-4-amino-pyridine, has been studied by single-crystal X-ray diffraction, multinuclear magic-angle spinning NMR, and first-principles density functional theory (DFT) calculations. Interpretation of the solid-state NMR data on the basis of calculated chemical shifts confirms the structure is primarily composed of molecules in the ground-state enol tautomer, whereas thermally activated cis-keto and photoisomerised trans-keto states exist as low-level defects with populations that are too low to detect experimentally. Variable temperature 13C NMR data reveal evidence for solid-state dynamics, which is found to be associated with fast rotational motion of t-butyl groups and 180° flips of the pyridine ring, contrasting the time-averaged structure obtained by X-ray diffraction. Comparison of calculated chemical shifts for the full crystal structure and an isolated molecule also reveals evidence for an intermolecular hydrogen bond involving the pyridine ring and an adjacent imine carbon, which facilitates the flipping motion. The DFT calculations also reveal that the molecular conformation in the crystal structure is very close to the energetic minimum for an isolated molecule, indicating that the ring dynamics arise as a result of considerable steric freedom of the pyridine ring and which also allows the molecule to adopt a favourable conformation for photochromism.",
keywords = "GIPAW calculations, NMR crystallography, photochromism, solid-state NMR",
author = "Dale, {Benjamin L.} and Halcovitch, {Nathan R.} and Peach, {Michael J.G.} and Griffin, {John M.}",
year = "2019",
month = "5",
day = "1",
doi = "10.1002/mrc.4805",
language = "English",
volume = "57",
pages = "230--242",
journal = "Magnetic Resonance in Chemistry",
issn = "0749-1581",
publisher = "John Wiley and Sons Ltd",
number = "5",

}

RIS

TY - JOUR

T1 - Investigation of structure and dynamics in a photochromic molecular crystal by NMR crystallography

AU - Dale, Benjamin L.

AU - Halcovitch, Nathan R.

AU - Peach, Michael J.G.

AU - Griffin, John M.

PY - 2019/5/1

Y1 - 2019/5/1

N2 - A photochromic anil, N-(3,5-di-t-butylsalicylidene)-4-amino-pyridine, has been studied by single-crystal X-ray diffraction, multinuclear magic-angle spinning NMR, and first-principles density functional theory (DFT) calculations. Interpretation of the solid-state NMR data on the basis of calculated chemical shifts confirms the structure is primarily composed of molecules in the ground-state enol tautomer, whereas thermally activated cis-keto and photoisomerised trans-keto states exist as low-level defects with populations that are too low to detect experimentally. Variable temperature 13C NMR data reveal evidence for solid-state dynamics, which is found to be associated with fast rotational motion of t-butyl groups and 180° flips of the pyridine ring, contrasting the time-averaged structure obtained by X-ray diffraction. Comparison of calculated chemical shifts for the full crystal structure and an isolated molecule also reveals evidence for an intermolecular hydrogen bond involving the pyridine ring and an adjacent imine carbon, which facilitates the flipping motion. The DFT calculations also reveal that the molecular conformation in the crystal structure is very close to the energetic minimum for an isolated molecule, indicating that the ring dynamics arise as a result of considerable steric freedom of the pyridine ring and which also allows the molecule to adopt a favourable conformation for photochromism.

AB - A photochromic anil, N-(3,5-di-t-butylsalicylidene)-4-amino-pyridine, has been studied by single-crystal X-ray diffraction, multinuclear magic-angle spinning NMR, and first-principles density functional theory (DFT) calculations. Interpretation of the solid-state NMR data on the basis of calculated chemical shifts confirms the structure is primarily composed of molecules in the ground-state enol tautomer, whereas thermally activated cis-keto and photoisomerised trans-keto states exist as low-level defects with populations that are too low to detect experimentally. Variable temperature 13C NMR data reveal evidence for solid-state dynamics, which is found to be associated with fast rotational motion of t-butyl groups and 180° flips of the pyridine ring, contrasting the time-averaged structure obtained by X-ray diffraction. Comparison of calculated chemical shifts for the full crystal structure and an isolated molecule also reveals evidence for an intermolecular hydrogen bond involving the pyridine ring and an adjacent imine carbon, which facilitates the flipping motion. The DFT calculations also reveal that the molecular conformation in the crystal structure is very close to the energetic minimum for an isolated molecule, indicating that the ring dynamics arise as a result of considerable steric freedom of the pyridine ring and which also allows the molecule to adopt a favourable conformation for photochromism.

KW - GIPAW calculations

KW - NMR crystallography

KW - photochromism

KW - solid-state NMR

U2 - 10.1002/mrc.4805

DO - 10.1002/mrc.4805

M3 - Journal article

AN - SCOPUS:85058498954

VL - 57

SP - 230

EP - 242

JO - Magnetic Resonance in Chemistry

JF - Magnetic Resonance in Chemistry

SN - 0749-1581

IS - 5

ER -