The novel use of NMR spectroscopy with in situ laser irradiation to study azo photoisomerisation

• Published in: Journal of photochemistry and photobiology. A, Chemistry. Chemistry., 2003, Vol.154 (2), p.179-188
• Main Authors: Tait, Katrina M, Parkinson, John A, Bates, Simon P, Ebenezer, Warren J, Jones, Anita C
• Format: Article
• Language: English
• Subjects: Azo dye; Chemistry; Cis–trans isomerisation; Exact sciences and technology; General and physical chemistry; Laser irradiation; NMR spectroscopy; Photochemistry; Photoisomerisation; Physical chemistry of induced reactions (with radiations, particles and ultrasonics)
• ISSN: 1010-6030; 1873-2666
• DOI: 10.1016/S1010-6030(02)00347-7

Cis–trans photoisomerisation of four azo dyes has been studied by 1 H nuclear magnetic resonance (NMR) spectroscopy, with in situ laser irradiation of the sample. The laser radiation was coupled into the sample within the NMR magnet via an optical fibre. This enabled the first 1 H NMR measurements to be made of the transient cis isomers of 4-(4-nitrophenylazo)aniline (CI Disperse Orange 3) and 4-[ N-ethyl- N-(2-hydroxyethyl)amino]-4′-nitroazobenzene (CI Disperse Red 1). Typical NMR methods, including 1 H 1D, 1 H – 1 H 2D COSY and 1 H – 1 H 2D EXSY/NOESY, were used to assign 1 H resonances of the trans and cis isomers. Ab initio calculations were used to predict the chemical shifts of cis- and trans-azobenzene, in good agreement with the experimental results, and to rationalise the chemical shift changes observed on isomerisation.