Synthesis And Properties Of Rhodamine-Based Ratiometric Fluorescence Sensors

Due to the low cost and high selectivity of fluorescent probes,many fluorescent probes for Hg²⁺detection have been developed in the past decade.Rhodamine dyes have attracted much attention due to their relatively long emission wavelengths and spironolactam platforms.This unique spirolactam platform among rhodamine dyes offers the opportunity to create fluorescent"on-off"sensors with large signal-to-noise ratios by using analyte-triggered fluorescence switching.Rhodamine dyes have long been favored by researchers because of their low toxicity,good water solubility,acid and alkali resistance,optical stability,and relatively long emission wavelengths.In this paper,based on the FRET mechanism,using the unique spirolactam structure of rhodamine as the recognition site,we designed and synthesized three kinds of rhodamine-based fluorescent sensors（naphthalimide and rhodamine fluorescent sensors Ra,methoxyl Naphthalimide and rhodamine fluorescence sensor Rb,chloromethylanthracene and rhodamine fluorescence sensor Rc）,and their detection mechanism was deeply studied by using ¹H NMR,ESI-MS and HPLC spectroscopy.Meanwhile,sensors Ra,Rb and Rc was successfully applied to the fluorescence imaging of intracellular and extracellular Hg²⁺.（1）Based on the FRET sensing mechanism,a ratiometric fluorescence sensor Ra of naphthalimide and rhodamine groups was designed and synthesized.In the CH₃CN/H₂O（4/1,v/v）system,the sensor Ra exhibits a ratiometric fluorescence response to Hg²⁺,the fluorescence color changed from green to orange,and the color of the solution changed from green to red by naked eye observation.Ra emission wavelength changes 38 nm.Furthermore,¹H NMR,ESI-MS and HPLC spectra were used to verify the possible mechanism of Ra detection of Hg²⁺.And the sensor was designed as a molecular keyboard lock and Hg²⁺detection for He La cells.（2）A colorimetric and ratiometric fluorescence sensor for Hg²⁺recognition with high selectivity based on the FRET mechanism of methoxynaphthalimide and rhodamine was designed and synthesized.The sensor Rb has high sensitivity,selectivity and proportional fluorescence response to Hg²⁺,the fluorescence color changes from cyan to orange,and the solution changes from colorless to pink in the CH₃CN/H₂O（1/1,v/v）system as observed with the naked eye color.After the addition of Hg²⁺,the pseudo-Stokes shift was 130 nm.Furthermore,a possible mechanism for the detection of Hg²⁺by the sensor Rb was proposed and verified by ESI-MS,¹H NMR and HPLC spectroscopy.（3）A novel fluorescence response sensor was designed and synthesized based on chloromethylanthracene and rhodamine.Compared with other metal ions,the sensor Rc has high sensitivity,high selectivity and ratiometric fluorescence response to Hg²⁺,the fluorescence color changes from purple to orange,and the visible solution changes from colorless to pink.After adding Hg²⁺,the pseudo-Stokes shift is as high as 174 nm.In addition,a possible mechanism for the detection of Hg²⁺was proposed,and the possible mechanisms for the detection of Hg²⁺by ¹H NMR,ESI-MS and HPLC spectroscopy were also verified.More importantly,the sensor Rc can be used for bioimaging applications in living cells.