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

Dale, Benjamin L. and Halcovitch, Nathan R. and Peach, Michael J.G. and Griffin, John M. (2019) Investigation of structure and dynamics in a photochromic molecular crystal by NMR crystallography. Magnetic Resonance in Chemistry, 57 (5). pp. 230-242. ISSN 0749-1581

[img] Text (PhotochromicNMR_revised_clean)
PhotochromicNMR_revised_clean.docx - Accepted Version
Available under License Creative Commons Attribution.

Download (1MB)

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.

Item Type: Journal Article
Journal or Publication Title: Magnetic Resonance in Chemistry
Uncontrolled Keywords: /dk/atira/pure/subjectarea/asjc/2500
Subjects:
ID Code: 134446
Deposited By: ep_importer_pure
Deposited On: 22 Jun 2019 08:53
Refereed?: Yes
Published?: Published
Last Modified: 17 Feb 2020 04:20
URI: https://eprints.lancs.ac.uk/id/eprint/134446

Actions (login required)

View Item View Item