Design,Synthesis And Bioimaging Applications Of Near-infrared Ratiometric Fluorescent Probes Based On Phenothiazine Platform

In recent years,the small organic molecule fluorescent probes have attracted widespread attention due to their high sensitivity,low toxicity and simple operation.Combined with fluorescence imaging technology,small organic molecule fluorescent probes can realize the monitoring of analytes in manners such as in situ real-time non-damage detection,low costing,high spatial and temporal resolution.Near-infrared ratiometric fluorescent probes have the potential to applied in medical research because of little injury,good biological tissue penetration ability,little auto-fluorescence interference,reduce interference by self-calibration,and it also can achieve sensitive detection as well as semi-quantitative or even quantitative detection.Phenothiazine derivatives are heterocyclic compounds plays an electron donor in the whole structure due to the electron-rich body caused by their own sulfur and nitrogen atoms.The 3,7 and 10 positions of phenothiazine are easy to be modified,which is conducive to the formation of intramolecular push-pull system,resulting in the red shift of emisson wavelength.Thus,it can be used in biosensors by functional modification design and synthesis responsive small molecule fluorescent probes.In this paper,phenothiazine was selected as fluorophore platform,two kinds of near-infrared ratiometric fluorescent probes to detect different analytes was synthesized,the corresponding spectral properties and biological imaging were studied.（Ⅰ）In the second chapter,C=N double bond was taken as SO₂recognition site,the fluorescence probe Ph-CN based on ICT mechanism and ESIPT mechanism for detecting SO₂was designed.Connected electron-donating phenothiazine and electron-withdrawing4-aminobenzenitrile with covalent bond to form ICT mechanism.Meanwhile,the hydrogen of the phenothiazine matrix and the nitrogen in the 4-aminobenzenitrile formed ESIPT mechanism.With both mechanisms working together,the probe Ph-CN emited red fluorescence,the maximum emission peak is 660 nm.After reacted with SO₂,the C=N double bond of the probe was broken,ICT and ESIPT mechanism were blocked,the emission peak at660 nm was blue shifted to 460 nm,thus achieved the ratio type detection of SO₂.The probe Ph-CN possessed advantages such as large stokes shift,rapid response time and could be successfully used for detecting SO₂in cells and mice.（Ⅱ）In the third chapter,benzothiazole acetonitrile was used as hydrazine response group,we synthesized a fluorescent probe PBT with AIE mechanism.Electron-donating phenothiazine and electron-withdrawing benzothiazole acetonitrile were connected by covalent bond to form a large conjugated structure.The maximum emission wavelength of the probe PBT is 690 nm.At the same time,benzothiazole acetonitrile acted as the characteristic group of AIE,giving the probe PBT AIE properties.After probe PBT reacted with N₂H₄,N₂H₄attacked the benzothiazole acetonitrile part of the probe,the benzothiazole acetonitrile was removed to form a hydrazone.The good push-pull system of the probe PBT was destroyed,the emission peak of 690 nm was blue shifted to 495 nm,so as to achieve the ratio type to detect hydrazine.The probe PBT had been successfully applied to the determination of gaseous hydrazine,and applied to zabrafish in vivo imaging.