Novel acridine-based thiosemicarbazones as “turn-on” chemosensors for selective recognition of fluoride anion: a spectroscopic and theoretical study

New thiosemicarbazide linked acridines 3a-c were prepared and investigated as chemosensors for the detection of biologically and environmentally important anions. The compounds 3a-c were found selective for fluoride (Fˉ) with no affinity for other anions i.e. ˉOAc, Brˉ, Iˉ, HSO4ˉ, SO4ˉ2, PO4ˉ3, ClO3ˉ, ClO4ˉ, CNˉ, and SCNˉ. Further, upon the gradual addition of fluoride anion (Fˉ) source (TBAF), a well-defined change in color of solution of probes 3a-c was observed. The anion sensing process was studied in detailed via UV-Vis absorption, fluorescence and 1H NMR experiments. Moreover, during the synthesis of acridine probes 3a-c nickel fluoride (NiF2), a rarely explored transition metal fluoride salt was used as catalyst. Theoretical studies via density functional theory (DFT) were also carried out to further investigate the sensing and anion (Fˉ) selectivity pattern of these probes.

本研究合成了一系列缩氨基硫脲连接的吖啶类探针3a-c，并将其作为化学传感器，用于检测具有重要生物学与环境意义的阴离子。实验发现，探针3a-c仅对氟离子（F⁻）具有识别选择性，而对其他阴离子如乙酸根（ˉOAc）、溴离子（Br⁻）、碘离子（I⁻）、硫酸氢根（HSO4⁻）、硫酸根（SO4²⁻）、磷酸根（PO4³⁻）、氯酸根（ClO3⁻）、高氯酸根（ClO4⁻）、氰根（CN⁻）及硫氰根（SCN⁻）均无结合亲和性。进一步实验表明，向探针3a-c的溶液中逐滴加入氟离子源四丁基氟化铵（TBAF）时，可观察到溶液颜色发生清晰可辨的变化。本研究通过紫外-可见吸收光谱、荧光光谱及氢核磁共振（¹H NMR）实验，对阴离子识别过程进行了详尽的探究。此外，在吖啶类探针3a-c的合成过程中，我们采用了鲜有报道的过渡金属氟化物盐——氟化镍（NiF₂）作为反应催化剂。本研究还通过密度泛函理论（DFT）开展了理论计算，以进一步阐明此类探针对氟离子的识别机制及阴离子选择性规律。