The substituent effect on the ESIPT and antioxidant activity of dual proton-transfer-site salicylaldehyde azine derivatives

Abstract

Antioxidants with excited state intramolecular proton transfer (ESIPT) typically demonstrate enhanced antioxidant efficacy. Herein, the substituent effect on ESIPT and antioxidant activity of a dual proton-transfer-site salicylaldehyde azine derivative HDBB was investigated using density functional theory (DFT) and time-dependent DFT. The results demonstrate that for molecules exhibiting two proton transfer sites, the antioxidant capacity is augmented after ESIPT. Substituents can promote ESIPT on one of the hydrogen bonds of HDBB while inhibiting it on the other. In addition, introducing the electron-donating group can effectively improve molecular antioxidant properties, offering a valuable reference point for the development of innovative antioxidants.