Tuning the Photoisomerization Mechanism of Oxindole Switches with Electron-Donating Substituents.

Abstract

This study investigates the photoreaction mechanism of a hydroxy-substituted oxindole photoswitch using femtosecond transient absorption, fluorescence up-conversion, and computational chemistry. Deprotonation of the hydroxyl group enhances the push-pull character in the molecule, allowing tuning of the photoisomerization mechanism from a precessional to an axial motion. The neutral form of the switch exhibits longer excited-state lifetimes, while the anionic form decays rapidly within 200 fs. Computational models show that deprotonation increases the charge transfer and accessibility to conical intersections. This work highlights how varying the electron-donating strength of a substituent in a push-pull photoswitch tunes the photoreaction mechanism in designing photoswitches.