Deprotonation-Induced Large Fluorescence Turn ON in a 2,4-Bis(benzo[ d ]thiazol-2-yl)phenol (HBT-BT) Derivative

作者：Kavinda M Arachchige, Brian Corbin, Pabasara Ediriweera, Michael Vrionides, C Salmon, Yi Pang, Tomoyasu Mani, W. M. C. Sameera, Chathura S. Abeywickrama · 发表于：The Journal of Physical Chemistry A · 年份：2025 · DOI：10.1021/acs.jpca.5c00446 · 被引用次数：11 · 研究领域：Luminescence and Fluorescent Materials、Photochemistry and Electron Transfer Studies、Radical Photochemical Reactions

2-(2′-Hydroxyphenyl)benzothiazole (HBT) is an interesting candidate that has been used to develop fluorescent probes with large Stokes’ shifts (Δλ > 100 nm) by utilizing excited-state intramolecular proton transfer (ESIPT). The efficiency of the ESIPT process in HBT is dependent on the acidity of the central phenolic group. The possible deprotonation of the enol form of HBT (PhOH → PhO – + H + ) can generate anionic form in solution that exhibits a noticeable hypsochromic effect in emission (λ em ≈ 475). By introduction of an appropriate substituent to the central phenolic ring, the ESIPT efficiency of the HBT can be controlled by modulating enol to anionic dynamic equilibrium. In this work, we extensively studied the solvent-dependent equilibrium of the 2- enol, 2- keto, and 2- anoinic species of the HBT derivative 2,4-bis(benzo[ d ]thiazol-2-yl)phenol ( 2 ) by steady-state and time-resolved fluorescence spectroscopy. Probe 2 was synthesized by attaching a second benzothiazole unit via a para phenylene linkage and was found to be significantly acidic. In comparison to parent HBT ( 1 ), probe 2 produced a highly emissive (λ em ≈ 475) 2- anionic species in solution by deprotonation. The 2- anionic was dominated in polar aprotic solvents such as DMF and DMSO and much weakly observed in nonpolar to moderately polar solvents. The solvent-dependent equilibrium was studied by 1 H NMR spectroscopy in different solvents. The formation of 2- anionic was found to be dependent on (a) th...