Substituent effects on the ESIPT process of H2O2 sensing product 1,3-bis(bispyridin-2-ylimino) isoindolin-4-ol: A theoretical study

Abstract

H₂O₂ plays an important role in a variety of physiological processes, but its overproduction or accumulation can lead to oxidative damage and related diseases, so it is crucial to establish accurate H₂O₂ detection methods. Fluorescence sensing as a potential method, the design and modulation of its luminescent properties are crucial to the detection results. In this work, we investigated the sensing mechanism of a novel H₂O₂ fluorescent probe (P1) and examined the role of substituent effects in modulating the fluorescence properties of its reaction products. The results show that the non-fluorescence property of the probe is due to twisted intramolecular charge transfer (TICT) mechanism resulting from a torsion of the excited state molecular conformation, and the fluorescence turn-on upon recognition of H₂O₂ by the probe is due to the reaction product (BBYI1) following the excited state intramolecular proton transfer (ESIPT) process. When the substituent is an electron-donating group, the energy barrier of the ESIPT reaction is lowered, promoting luminescence, while the electron-withdrawing group has the opposite effect. In summary, the present work may offer a theoretical foundation for the development of more sensitive fluorescent probes for ESIPT-based H₂O₂ detection.