The mechanisms of 2-(Benzo[d]thiazol-2-yl)phenol-based bifunctional probe (HBT-FS) for detecting fluoride (F⁻) and sulfite (SO₃^2–) based on excited-state intramolecular proton transfer (ESIPT) and intramolecular charge transfer (ICT) have been theoretically studied. Laplacian bond order of HBT-FS indicates that the F⁻ ion cleaves the Si-O bond and then forms Compound 2 possessing a six-membered ring with a hydrogen bond. Potential energy curves and dynamic simulations confirm that ESIPT in Compound 2 occurs along with this hydrogen bond and forms a keto structure with an emission at 623 nm, which agrees with the observed experimental value (634 nm) after adding F⁻. Therefore, the fluorescence red-shift (from 498 to 634 nm) of HBT-FS observed in experiment after adding F⁻ is caused by ESIPT. The SO₃^2– ion is added to the C₅ site of HBT-FS, which is confirmed by orbital-weighted dual descriptor, and then forms Compound 3 with fluorescence located at 404 nm. The experimentally measured fluorescence at 371 nm after adding SO₃^2– is assigned to Compound 3. Charge transfer analyses indicate that the ICT extent of Compound 3 is relatively weak compared with that of HBT-FS because of the destruction of the conjugated structure by the addition reaction of SO₃^2–, which induces the blue-shift of the fluorescence of HBT-FS from 498 to 371 nm. The different fluorescence responses make HBT-FS a fluorescent probe to discriminatorily detect F⁻ and SO₃^2–.

中文翻译：

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基于激发态分子内质子转移和分子内电荷转移的双功能荧光探针检测氟化物和亚硫酸盐的机制

基于激发态分子内质子转移的 2-(Benzo[d]thiazol-2-yl) 苯酚基双功能探针 (HBT-FS) 检测氟化物 (F ^- ) 和亚硫酸盐 (SO ₃ ^2- ) 的机制（ ESIPT) 和分子内电荷转移 (ICT) 已在理论上进行了研究。HBT-FS 的拉普拉斯键序表明 F ^-离子裂解 Si-O 键，然后形成具有带氢键的六元环的化合物 2。势能曲线和动态模拟证实，化合物 2 中的 ESIPT 与该氢键一起发生并形成酮结构，在 623 nm 处发射，这与添加 F ^-后观察到的实验值（634 nm）一致. 因此，实验中观察到的 HBT-FS 添加 F ^-后的荧光红移（从 498 到 634 nm）是由 ESIPT 引起的。SO ₃ ^2-离子加入HBT-FS的C ₅位点，通过轨道加权双描述符确认，然后形成化合物3，荧光位于404 nm。添加 SO ₃ ^2–后在 371 nm 处实验测得的荧光归于化合物 3。电荷转移分析表明，与 HBT-FS 相比，化合物 3 的 ICT 程度相对较弱，因为共轭结构被共轭结构破坏。 SO ₃ ^2-的加成反应，这会导致 HBT-FS 的荧光从 498 nm 蓝移到 371 nm。不同的荧光响应使 HBT-FS 成为一种荧光探针，可以区分检测 F ^-和 SO ₃ ^2-。