Comparison of experimental and calculated 1H NMR chemical shifts of geometric photoisomers of azo dyes

Structural characterisation of the photoisomers of reactive sulfonated azo dyes by NMR spectroscopy and DFT calculations

“…Density functional theory (DFT) calculations of the structures of trans and cis isomers and their 1 H NMR chemical shifts were used to rationalise characteristic changes in the NMR spectrum on photoisomerisation. 21 Our results revealed a key NMR diagnostic of formation of the cis form of azo dyes possessing an azobenzene construct, namely a large (ca.1 ppm) shift to lower frequency of the 1 H NMR resonances associated with aromatic protons ortho to the azo linkage. We now report application of this technique to a molecular system of comparable complexity to those of modern, commercial textile dyes.…”

Spectroscopic studies of Solophenyl red 3BL polyazo dye tautomerism in different solvents using UV–visible, 1H NMR and steady-state fluorescence techniques

“…Alarcon et al have reported fluorescence and absorption data for substituted hydroxybenzaldehydes and have found that emission comes only from the hydrazone form ( [6] and references therein). In colourant industry, colour constancy is strongly depended on cisetrans isomerism of dyes [16]. The shift of tautomeric equilibrium was observed in different azo compounds by adding acids or alkalis into solvents, or by changing temperature.…”

Functionalising the azobenzene motif delivers a light-responsive membrane-interactive compound with the potential for photodynamic therapy applications

“…The changes in the 1 H NMR of 4 were compared prior to irradiation, after 21 h of 365 nm irradiation, and after exposure of the irradiated sample to darkness and heat or 532 nm light (to promote relaxation back to trans-4). The spectra (ESI †) show an expected upfield shift occurs upon irradiation of trans-4, 12 giving a spectrum which is consistent with the cis-conformation (5). Similarly, a switch back to the trans-conformer (4) occurs with 532 nm light or at 60 °C in the dark.…”