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Tautomers and UV-Induced Photoisomerization of a Strongly Intramolecularly H‑Bonded Aromatic Azo-Dye: 1‑(Cyclopropyl)diazo-2-naphthol

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journal contribution
posted on 17.10.2013, 00:00 by Luís Duarte, Barbara Michela Giuliano, Igor Reva, Rui Fausto
Aromatic azo compounds have a wide range of industrial applications as dyes in optical and color-changing materials and can also be exploited in the design of new photodynamic molecular systems. The azo derivative 1-(cyclopropyl)­diazo-2-naphthol was isolated in low-temperature cryogenic matrices, and its molecular structure, tautomeric equilibrium, and photochemical transformations were characterized by infrared spectroscopy and theoretical calculations. Only azo–enol forms having the OH group involved in a strong intramolecular hydrogen bond, forming a six-membered ring with the azo group, were found experimentally. Irradiation with a narrowband source in the near-UV range generates different rotameric and tautomeric azo–enol and keto–hydrazone forms that can be interconverted at different irradiation wavelengths.