Unlocking the Fluorescent Colour Code of Probe PBQ: Theoretical Study of the Magic Switch On/Off Mechanism for Excited-State Proton Transfer

作者：Xiaotong Guan, Jiaan Gao, Yuhang Sun, Yang Wang, Hui Li, Guangyong Jin · 发表于：The Journal of Physical Chemistry A · 年份：2025 · DOI：10.1021/acs.jpca.5c00151 · 被引用次数：3 · 研究领域：Photochemistry and Electron Transfer Studies、Molecular Sensors and Ion Detection、Luminescence and Fluorescent Materials

), employing DFT and TD-DFT. Computational results showed that PBQ underwent the coupled process of TICT and ESIPT. It was further explained that the experimentally observed dual fluorescence phenomenon originated from the co-contribution of the enol* and keto* forms. Interestingly, although the fluorescent product (PBQ-1) had the same proton transfer site with PBQ, only a single fluorescence was observed in the experiment. We hypothesized that the monofluorescence phenomenon was caused by the fluorescence quenching of the keto* form. From the perspective of TICT, PET, and ISC analysis, we confirmed in reverse that if the PT state existed, then fluorescence in the keto* form must have also existed. In contrast, hole-electron and PES analysis revealed that PBQ-1 had a higher energy barrier and weaker ICT in the enol* state than PBQ, thereby necessarily prohibiting the ESIPT process. The results further confirmed that the fluorescence observed in PBQ-1 originates solely from the enol* state. This study provided a comprehensive understanding of the fluorescent probe photophysical mechanism for PBQ and guidance for designing novel ESIPT-based fluorescent probes for chemical sensing.