Title
Mechanistic Insight into Para‐Substituent Control of Thermal Half‐Lives in Arylazopyrazole Photoswitches
Author
Katharina Schlögl
Institute of Applied Synthetic Chemistry, TU Wien
Dominik Dreier
Institute of Applied Synthetic Chemistry, TU Wien
... show all
Abstract
Arylazopyrazoles are versatile photoswitches with excellent photochromic properties and tunable thermal half-lives, yet the mechanistic role of substituents in controlling thermal stability remains poorly understood. Here, we synthesized an extensive library of arylazo-1,3,5-trimethylpyrazole photoswitches and rationalized the influence of para-substituents on the thermal half-lives, finding excellent agreement between calculated and measured trends. Calculations show that the electron-donating and electron-withdrawing nature of the substituents modulates the back-isomerization process through at least two distinct mechanisms. Strong electron-donating groups enhance delocalization at the azo moiety and thus favor a nonadiabatic out-of-plane rotational pathway via the lowest triplet state. In contrast, strong electron-withdrawing groups reduce delocalization and promote a conventional ground state in-plane inversion mechanism. Intermediate substituents exhibit a gradual shift that combines both major mechanisms. These findings provide prospects for rational design of responsive photoswitches with controllable thermal stability, essential for in vivo applications.
Keywords
Azo compoundsDensity functional calculationsIsomerizationPhotoswitches
Object type
Language
English [eng]
Persistent identifier
Appeared in
Title
Angewandte Chemie International Edition
Volume
64
Issue
43
ISSN
1433-7851
Issued
2025
Publication
Wiley
Version type
Date issued
2025
Access rights
Rights
Rights statement
© 2025 The Author(s)
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