氨基硫脲-罗丹明6G荧光探针的合成及对Hg^(2+)的选择性识别

Synthesis of a thiourea-based amine rhodamine derivative chemo probe and its Hg^(2+)-selective recognition properties

设计合成了一个基于氨基硫脲和罗丹明6G的衍生物作为金属阳离子检测探针,其结构得到核磁和X射线单晶衍射分析确认,研究了其对汞离子的选择性识别性能。结果表明,含水体系中,探针在汞离子诱导下生成分子内胍类衍生物,伴随罗丹明螺酰内环开环,荧光信号实现由“关”到“开”的状态变化。在551 nm处荧光强度随着汞离子的加入呈现显著的线性增强,同时溶液颜色由无色变为粉色。该探针对环境中汞离子有高灵敏度和高选择性,可以实现荧光和显色双重传感检测。

Rhodamine derivatives are excellent fluorescent probes and have shown sharp descending trends of emission intensity on interacting with a specific analyte which reasons for the opening of the spirolactam ring.We describe the synthesis and characterization of a rhodamine 6G derivative with bearing a thiourea-based amine fluorescent ligand 1-(2-(3′,6′-bis(ethylamino)-2′,7′-dimethyl-3-oxospiro[isoindoline-1,9′-xanthen]-2-yl)ethyl)-3-(pyridin-2-yl)thiourea(RhS,Figure 1).The structure of RhS is confirmed by X-ray crystallography in addition to NMR.The free RhS in methanol and aqueous solution is non-fluorescent due to the quenching of spirolactam structure in rhodamine 6G.Its preliminary application as a chemo probe for Hg^(2+)at room temperature.In the absorption spectra,RhS shows bands at 534 nm in the presence of Hg^(2+).This metal ion turns the colorless solution of the probe to pink.Most importantly,the probe solves the problem of serious interferences from other transition metal ions such as Li^(+),Na^(+),K^(+),Ca^(2+),Cs+,Mg^(2+),Mn^(2+),Co^(2+),Ni^(2+),Cu^(2+),Zn^(2+),Cd^(2+),Ag+,Fe^(2+),Cr^(3+)and shows a fast response toward Hg^(2+).RhS is almost non-fluorescent when it is excited at 492 nm.But in the presence of Hg^(2+),the emission intensity at 551 nm increases massively.No other metal ion can cause significant enhancement of the emission intensity.Fluorescence spectroscopy is used to monitor the viable pH range,and RhS can bear a broad pH span(5.5~8.0).In addition,the sensing mechanism toward Hg^(2+)is discussed.The fluorescent signal change of the probe is based on the mercury-promoted intramolecular cyclic guanidine derivative and the ring-opening process of the rhodamine spirolactam.Ring-opening and the subsequent complex formation with the metal ion are confirmed by MS.Thus rhodamine-based thiourea derivative chemo probe gave rise to a sensitive dual chromo-and fluorogenic observation induced by Hg^(2+).