Arachchige Kavinda M, Corbin Brian, Ediriweera Pabasara, Vrionides Michael A, Salmon Carrie, Pang Yi, Mani Tomoyasu, Sameera W M C, Abeywickrama Chathura S
Department of Pharmaceutical Sciences, University of Connecticut, Storrs, Connecticut 06269, United States.
Department of Chemistry, The University of Akron, Akron, Ohio 44325, United States.
J Phys Chem A. 2025 May 15;129(19):4189-4203. doi: 10.1021/acs.jpca.5c00446. Epub 2025 May 5.
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 form of HBT (PhOH → PhO + H) can generate form in solution that exhibits a noticeable hypsochromic effect in emission (λ ≈ 475). By introduction of an appropriate substituent to the central phenolic ring, the ESIPT efficiency of the HBT can be controlled by modulating to dynamic equilibrium. In this work, we extensively studied the solvent-dependent equilibrium of the , , and species of the HBT derivative 2,4-bis(benzo[]thiazol-2-yl)phenol () by steady-state and time-resolved fluorescence spectroscopy. Probe was synthesized by attaching a second benzothiazole unit via a phenylene linkage and was found to be significantly acidic. In comparison to parent HBT (), probe produced a highly emissive (λ ≈ 475) species in solution by deprotonation. The 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 H NMR spectroscopy in different solvents. The formation of was found to be dependent on (a) the type of solvent and (b) the presence of basic anionic species (i.e., fluoride). The photophysical properties (absorbance and emission) of probe were investigated in different solvent environments and in the presence of different anionic species to understand the dynamic equilibrium that leads to the generation of in solution. The fluorescence lifetime measurements of in different solvents revealed the existence of , , and species. Also, the fluoride-induced transformation of to was studied by fluorescence lifetime measurements. The density functional theory (DFT)-based computational calculations were performed to evaluate the electronic nature of the dynamic equilibrium that produced . Computational studies, employing density functional theory (DFT) and time-dependent density functional theory (TD-DFT), confirmed that the species is stable in the ground state, while upon excitation, species undergoes ESIPT spontaneously. Computed absorption and emission wavelengths showed good agreement with the experimental results.
2-(2'-羟基苯基)苯并噻唑（HBT）是一种引人关注的化合物，通过利用激发态分子内质子转移（ESIPT），它被用于开发具有大斯托克斯位移（Δλ > 100 nm）的荧光探针。HBT中ESIPT过程的效率取决于中心酚羟基的酸度。HBT的 形式（PhOH → PhO⁻ + H⁺）可能发生的去质子化会在溶液中产生 形式，其发射光谱表现出明显的蓝移效应（λ ≈ 475）。通过在中心酚环上引入合适的取代基，可以通过调节 与 之间的动态平衡来控制HBT的ESIPT效率。在这项工作中，我们通过稳态和时间分辨荧光光谱广泛研究了HBT衍生物2,4-双（苯并[]噻唑-2-基）苯酚（）的 、 和 物种的溶剂依赖性平衡。探针 通过亚苯基连接附着第二个苯并噻唑单元合成，发现其酸性显著。与母体HBT（）相比，探针 通过去质子化在溶液中产生了高发射性（λ ≈ 475）的 物种。 在极性非质子溶剂如DMF和DMSO中占主导，而在非极性到中等极性溶剂中观察到的程度要弱得多。通过¹H NMR光谱在不同溶剂中研究了溶剂依赖性平衡。发现 的形成取决于（a）溶剂类型和（b）碱性阴离子物种（即氟化物）的存在。在不同溶剂环境和不同阴离子物种存在的情况下研究了探针 的光物理性质（吸光度和发射），以了解导致溶液中 生成的动态平衡。在不同溶剂中对 的荧光寿命测量揭示了 、 和 物种的存在。此外，通过荧光寿命测量研究了氟化物诱导的 向 的转变。进行了基于密度泛函理论（DFT）的计算，以评估产生 的动态平衡的电子性质。采用密度泛函理论（DFT）和含时密度泛函理论（TD-DFT）的计算研究证实， 物种在基态是稳定的，而在激发时， 物种会自发发生ESIPT。计算得到的吸收和发射波长与实验结果吻合良好。
