Chemical Z-E Isomer Switching of Arylazopyrazoles Using Acid

Arylazopyrazoles show significant potential as next-generation photoswitches, in particular because of the high thermal stability of their Z-isomers. Herein we investigate the potential to perform Z-E isomer chemical switching of arylazopyrazoles using acid. We show that acid-accelerated isomerisation allows for robust Z-E switching using mild acids and opens up the possibility to use light-acid cycles to near quantitatively and reversibly switch the arylazopyrazoles at room temperature. We attribute the chemical switching to azonium formation, facilitated by mesomeric stabilisation by the pyrazole ring. Coupled with their exceptionally long Z-isomer half-lives, we believe our study may open up a wider array of functional opportunities for the arylazopyrazoles.