Synthesis And Properties Of Rhodamine-based Fluorescence Sensor For Detecting Hg²⁺

In recent years,organic fluorescent sensors have attracted the attention of more and more researchers due to their advantages of low price,convenient detection and high accuracy.Subsequently,fluorescent sensors based on different theories have been developed one after another.Among all kinds of fluorescent functional groups,rhodamine is favored by people because of its long emission wavelength,low biological toxicity and obvious color change of solution.Among all kinds of sensors based on rhodamine,most of them use the characteristics of rhodamine for identification.In terms of ion recognition,heavy metal ions and various organic small molecules are preferred.With the spirolactam ring of the rhodamine group as recognition sites,this paper designed and synthesized three of specific recognition of rhodamine fluorescence sensors for Hg²⁺（fluorescent sensors based on naphthalene-rhodamine,fluorescent sensors based on dansyl-rhodamine,fluorescent sensors based on naphthalimide-rhodamine）.It has carried on the thorough research on its detection mechanism,and successful application in the fluorescent imaging of the cell.The main research contents of this paper are generalized as follows:In the first chapter,the development process,response mechanism,practical application and research status of sensor based on Hg²⁺are introduced.At the same time,the research content of this paper is put forward in combination with the current development situation.In the second chapter,a fluorescent sensor based on rhodamine platform is developed to detect Hg²⁺.The results of detection show that the sensor has high selectivity and good anti-interference ability for Hg²⁺recognition even in the presence of other metal ions(except for Cu²⁺).Both fluorescence and absorption spectra show good linear ranges and low detection limits（0.38μM and 0.12μM）.In addition,the response mechanism between sensor and Hg²⁺is well explained.It is worth noting that the sensor successfully uses the test strips to detect the solution color of metal ions and identify the concentration gradient of Hg²⁺,which perfectly demonstrates the colorimetric recognition.The use of cell imaging adds another bright spot to the sensor.In the third chapter,a fluorescent sensor based on the fluorescence resonance energy transfer（FRET）mechanism is designed and synthesized,which is composed of dansyl-rhodamine.The chemical sensor can specifically detect Hg²⁺.Rhodamine,danoyl chloride and hydrazide are selected as energy receptors,donors and reaction sites,respectively.The sensor has a high selectivity and sensitivity to Hg²⁺.Under the premise of complexing with Hg²⁺,the structure of spirolactam ring is hydrolyzed by water,and the color of the solution can be better recognized through the naked eye.The difference between the emission peaks before and after detection is 31 nm,which effectively reduces the interference of various factors and makes it more accurate.In He La cells,the sensor’s successful imaging gives the opportunity to reveal change of complex processes in the organism.In the fourth chapter,a ratiometric fluorescent chemical sensor based on naphthalimide-rhodamine is developed through multi-step synthesis.Sensor specifically recognizes Hg²⁺in a variety of metal ions,showing a highly sensitive fluorescence response to Hg²⁺.Importantly,the sensor can perform trace detection as well as ratiometric detection,showing a lower detection limit.Ultraviolet identification of the naked eye is another new bright spot of the sensor.The detection mechanism of the sensor has been well explained by multiple verifications of ESI-MS,¹H NMR and HPLC spectra.In addition to Hg²⁺detection,naphthalimide-rhodamine sensor has been shown to be effective for cell imaging.