A series of new symmetrically functionalized guanidinium chlorides (S1–S10) are synthesized in good yields and their sensing ability toward anions is studied in MeCN–DMF (24 : 1) (v/v). The absorption bands of these molecules in the presence of anions are tuned by varying the functional groups attached to the guanidinium moiety (which resembles urea) with respect to (i) aromaticity (S1–S4), (ii) electron induction effect (S1, S5–S9), (iii) positional isomeric effect (S7–S9), (iv) indole functionality (S10) of the conjugated aryl units. Anions that are above Cl− in the Hofmeister series (F−, AcO−, H2PO4−) are eligible as an analyte in this series of molecules whereas less basic anions than Cl− do not cause any interference. Thus, this series of molecules are suitable for the detection of anions in the narrow window of the Hofmeister series. Out of all the anions, only fluoride causes vivid colour changes from yellow to red to reddish orange and finally to blue, irrespective of the increasing aromaticity, induction and positional isomeric effect of the substituent that is attached to the guanidinium moiety. Interestingly, S9 has shown the ability to sense distinctly both F− and AcO− colourimetrically. Further S10, a sensor attached with indole functionality shows selective sensing of F− colourimetrically with a NIR signature at ∼930 nm though both these outputs are very unstable in nature. Stability constants for complex formation of S1–S10 (except S5) with F−, AcO− are calculated by UV–vis titration experiments. Finally single crystal X-ray structural studies on the species 1 formed upon treating S6 with sodium fluoride confirms -NH deprotonation, whereas the reaction of S6 and S2 with sodium benzoate shows 1 : 1 host : guest binding that results in complexes 2 and 3 respectively.
一系列新型对称功能化的
氨基甲酸铵氯化物(S1–S10)以良好的产率合成,并研究其在MeCN–
DMF (24 : 1) (v/v)中对阴离子的感应能力。这些分子在阴离子存在下的吸收带通过改变附加在
氨基甲酸铵基团(类似于
尿素)上的功能基团而调控,涉及(i)芳香性(S1–S4),(ii)电子诱导效应(S1,S5–S9),(iii)位置异构效应(S7–S9),(iv)
吲哚功能性(S10)等共轭芳基单元。霍夫迈斯特系列中优于Cl−的阴离子(F−,AcO−,H2PO4−)皆可作为该系列分子的分析物,而与Cl−相比,碱性较弱的阴离子不会造成任何干扰。因此,这系列分子适合在霍夫迈斯特系列的狭窄窗口中检测阴离子。在所有阴离子中,只有
氟离子导致显著的颜色变化,从黄色变为红色,再变为红橙色,最后变为蓝色,这与附加在
氨基甲酸铵基团上的芳香性、诱导效应和位置异构效应的增加无关。有趣的是,S9在颜色计测上能够清晰地感知F−和AcO−。此外,附有
吲哚功能的传感器S10表明在颜色计测中选择性地感知F−,在大约930 nm处具有近红外特征,尽管这两种信号本质上都非常不稳定。通过紫外-可见光滴定实验计算的S1–S10(除了S5)与F−、AcO−的配合物形成稳定常数。最后,针对用
氟化
钠处理S6形成的物种1进行的单晶X射线结构研究确认了-NH去质子化,而S6和S2与
苯甲酸钠的反应则显示出1:1的主客体结合,分别形成配合物2和3。