| The design and synthesis of fluorescent probes has been a hotspot research of current analytical chemistry.Fluorescent analysis technology has been widely used in chemical, environmental science, materials chemistry and biomedical and other fieldsbecause of its fast analysis speed, good selectivity, simple operation, high sensitivity, etc.Rhodamine derivatives are a kind of very important fluorescent probe dyes. They have excellent properties such as: big conjugate and rigid structure, good photostability, high fluorescence quantum yield, long emission wavelength, largemolar absorption coefficient, and low cost.Therefore, it is a kind of excellent fluorophore. By modifying the fluorescence moieties of rhodamine B compounds, in this paper, we synthesized a series of fluorescent probes, which can be applied in the detectionof Hg2+ and Cr3+ respectively. Besides, the two fluorescent probes are based on rhodaminespirolactam "off- on" mechanism. Details are as follows:Firstly,we designed and synthesized two fluorescent probes named R1, R2. And their structures were identified and characterized by mass spectrometry and nuclear magnetic resonancespectrums.Secondly,arhodaminespirolactam derivative(R1) bearing a hydrophilic carboxylic acid groupis developed as a fluorescent chemodosimeter for bivalent mercury ions(Hg2+) in 100% aqueous solution.It exhibits a highly sensitive enhanced fluorescent response toward Hg2+ with a 42-fold fluorescence intensity enhancement under 1 equiv. of Hg2+ added.The fluorescent probe can be applied to the quantification of Hg2+ with a linear rangecovering from 3.0 × 10-7 to 1.0 × 10-5 M and a detection limit of 9.7 × 10-8M. Most importantly, the fluorescence changes of the chemodosimeter are remarkablyspecific for Hg2+ in the presence of other metal ions, which meet the selective requirements for practicalapplication. Moreover, the experiment results show that the response behavior ofR1 towards Hg2+ is pHindependent in neutral condition(pH 5.0-8.0) and the response of the probe is fast(responsetime less than 3 min). Furthermore, the ring-opening mechanism of the rhodamine spirolactam induced by Hg2+ is supported by NMR, MS and DFT theoretical calculations. In addition, the proposed fluorescent probe has been used todetect Hg2+ in water samples and image Hg2+ in livingcells with satisfying results.Finally,we developed another rhodamine derivative(R2) as a fluorescent probe for trivalent chromium ions(Cr3+). We find that before adding Cr3+, the probe R2 is colorless and almost no fluorescenceemission. However, upon the addition of Cr3+, we can see that the probe R2 has strong fluorescence emission of rhodamine, the color of the solution also change from colorless to pink, because the probe can react with Cr3+, inducing the rhodamine B lactam to be opened. Experimental results show that the linear response range of fluorescent probe R2 to Cr3+is 5.0 ×10-7 to2.0 ×10-5 M and the detection limit is 1.7×10-7 M. What's more, the response is almost not affected by the pH within the range of 6.0 to 8.0. Most importantly, the fluorescence changes of the the probe are remarkably specific for Cr3+in the presence of other metal ions. We also use the method of DFT theoretical calculation to study the response of fluorescent probe R2 to Cr3+. In addition, the proposed probe R2 has been used to detect Cr3+ in real water samples and image Cr3+in living cells with satisfying results. |
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