Synthesis Of Rhodamine-based Fluorimetric/C Olorimetric Probes And Detection Of Fe³⁺ In Water

With the development of science and technology,more and more factories are spring up,but industrial pollution is also increasing day by day.Waste water,sewage,and air pollution pose a great threat to human health.The soil and water pollution induced by heavy metals becomes more serious,leading to many life-threatening diseases.Therefore,it is necessary to detect toxic metals ions.In this thesis,three kinds of fluorimetric/colorimetric probe molecules based on rhodamine derivatives were designed,synthesized,and characterized.Their detection performancefor Fe³⁺ions in water was studied.The details are as follows:1.A fluorescence probe for the detection of Fe³⁺ions was synthesized based on the aromatization reaction of 3-dehydroshikonic acid methyl ester.The probe molecule RhM606 was prepared by the reaction of rhodamine 6G with ethylenediamine,followed by the condensation reaction of 3-dehydrohummatic acid methyl ester under p-toluenesulfonic acid.In the Tris-HCl buffer system（pure water）at pH=6,a coordination between RhM606 and Fe³⁺ions resulted in the ring opening of rhodamine lactam.An absorption peak occurred at 530 nm,and the solution changed from the original colorless to pink.At the same time,the solution emitted a strong fluorescence emission at 557 nm.The interference experiment proved that the probe has good selectivity to Fe³⁺ions;the titration experiment confirmed that the probe molecule can quantitatively detect Fe³⁺ions in water with a limit of detection（LOD）of 3.93μM.The results show that the probe molecule can detect Fe³⁺ions in water with high sensitivity and selectivity.2.The probe RhM716 was prepared by reacting an intermediate compound of rhodamine 6G and ethylenediamine and 3,5-dibromo-4-hydroxybenzaldehyde.The selectivity of the probe to different metal ions was studied by colorimetric-fluorescence method.The effects of solution pH,response time and concentration of metal ions on fluorescence intensity and absorbance were investigated.The results showed that a coordination occurred between RhM716 and Fe³⁺in the ethanol solution at pH=6,leading to an absorption peak at 530 nm.The solution changed from the original colorless to pink.Simultaneously,a strong fluorescence was emitted at 550 nm and the probe has a good selectivity to Fe³⁺ions.As a colorimetric probe,the absorbance at 530nm of RhM716 showed a good linear relationship in the range of 10-45μM for Fe³⁺concentration.The LOD was 1.26μM.As a fluorescent probe,the fluorescence intensity at 550 nm of RhM716 exhibited a good linear relationship in the range of 10-50μM,leading to a LOD of 3.88μM.In addition,the detection reversibility of the probe molecule can be achieved by the coordination of ethylenediaminetetraacetic acid（EDTA）with Fe³⁺ions.The Job’s curve indicated that RhM716 was complexed with Fe³⁺in a ratio of 1:1.Therefore,RhM716 is a good colorimetric/fluorimetric probe for the detection of Fe³⁺ions.3.Rhodamine derivative RhM668 was synthesized by the reaction between Rhodamine B hydrazide and 3-hydroxy-4-methoxy-2-bromobenzaldehyde and characterized by nuclear magnetic resonance.The probe showed a good fluorimetric and colorimetric response to Fe³⁺in a Tris-HCl buffer system at pH=7.As a colorimetric probe,RhM668 can specifically bind to RhM668 and produce an absorption peak at 550nm.The solution changed from colorless to purple.A LOD of 2.46μM was obtained.As a fluorescent probe,Fe³⁺ions can coordinate with RhM668 selectively to emit fluorescence at 570 nm.The LOD was 3.88μM.The Job’s curve demonstrated that RhM668 is complexed with Fe³⁺in a ratio of 1:1.In addition,EDTA can recapture the Fe³⁺ions that have been coordinated with RhM668,resulted in a reversible detection.Therefore,the as-designed colorimetric/fluorimetric probe molecule can detect Fe³⁺ions in the aqueous solution with highly selectivity and reversibility.