Structural characterisation of the photoisomers of reactive sulfonated azo dyes by NMR spectroscopy and DFT calculations.
1H NMR spectroscopy coupled with in situ laser irradiation has been used together with density functional theory (DFT) computation to examine the structures of the photoisomers of a series of sulfonated reactive azo dyes. Assignment of 1H NMR spectra acquired at the photostationary state has allowed, for the first time, NMR characterisation of unstable cis isomers of commercially relevant water-soluble azo dyes. Structural features of the two isomeric forms predicted by DFT calculations are clearly reflected in the experimental NMR data. The trans-cis photoisomerisation process could be unambiguously identified in each case, based on the large chemical shift change observed for resonances associated with aromatic protons adjacent to the azo linkage.
Tait
Katrina M
KM
School of Chemistry, The University of Edinburgh, West Mains Road, Edinburgh, UK.
Parkinson
John A
JA
Gibson
David I
DI
Richardson
Patricia R
PR
Ebenezer
Warren J
WJ
Hutchings
Michael G
MG
Jones
Anita C
AC