The curious case of the photochemistry of 2-hydroxyphenylazo-3,5-dimethylisoxazole: unravelling the process among tautomerization, photoisomerization, and conformational changes

Abstract

Considering the growing interest in azoheteroarene photoswitches, the molecular level process underlying photochemistry is intriguing. In our earlier investigation on phenylazo-3,5-dimethylisoxazole, besides E–Z photoisomerization, we also observed light-induced phase transition that supports the possible conformational changes under neat conditions. Furthermore, hydrogen bond-forming groups such as –OH, at the ortho position to the azo chromophore, can potentially hamper the isomerization through tautomerism. All of them develop a curiosity in the photochemical outcome of 2-hydroxyphenylazo-3,5-dimethylisoxazole (HPAI, 1). Herein, we report the photochemistry of HPAI in an argon matrix at 4 K, followed by infrared spectroscopy. Through experiments and computations, we identified the E–Z photoisomerization in HPAI as the only observed channel among the above-mentioned possibilities.