Research On Isomerization And Chemical Sensing Application Based On 1,8-Naphthalimide

In recent years,the research and application of fluorescent chemical sensors have made great progress.The test conditions have changed from organic solvents to aqueous solutions,among them,the research on toxic metal ions and molecular sensing has become a research hotspot.Traditional detection methods have many disadvantages,like expensive,time-consuming,low accuracy and poor qualitative ability,but fluorescence technology has attracted considerable research due to its low cost,fast response speed,high sensitivity and simple operation.Classical naphthalimide fluorophores are widely used in colorimetric probes and photochemical sensors due to their excellent optical properties,such as strong absorption in the visible light region,high light stability and large Stokes shift.Chapter 1:In this chapter,an overview of the composition of the fluorescent chemical sensor(recognition group,connector part and luminescent group)was given,and then the recognition principle of fluorescent chemical sensor was introduced in detail,such as Intramolecular Charge Transfer(ICT),Photoinduced Electron Transfer(PET),Fluorescence Resonance Energy Transfer(FRET),Excited-State Intramolecular Proton Transfer(ESIPT),excimer association mechanism…The research status of 1,8 naphthalimide-based fluorescent chemical sensors was reviewed,it was widely used in the fields of ions detection,moleculars recognition,materials application and bioimaging.Finally,the phenomenon of enol-keto tautomerism and research methods were briefly explained.Chapter 2:In this chapter,a Schiff base molecule S5 based on 1,8 naphthalimide was designed and synthesized.Among the synthesis,the method has been continuously improved,and the reaction intermediate S3 was obtained in a high yield while avoid useing highly toxic catalysts;a green and high-yield solvent-free grinding synthesis method was also found when synthesizing S5.After the illumination of 254 nm light,the Schiff base undergoes isomerization cyclization.As the light time increased,the absorption peak at 355 nm gradually increased,and the absorption peak at 445 nm gradually fade away,and the fluorescence intensity increased significantly about 250 times.The copper ion coordination experiment and the significant changes of ~1H NMR and Infrared Spectroscopy,which confirmed the structural transformation of Schiff base molecular photocyclization.As the same time,the hydrogen-produced experiment provided a new solution for liquid organic hydrogen storage.The mechanism of cyclization has been reasonably explained by free radical capture experiment.In addition,the expansion of Schiff base substrates also provided a general strategy for the photocyclization of Schiff bases.Chapter 3:In this chapter,three fluoride ion probes N1,N2,N3 based on 1,8 naphthalimide were designed and synthesized.In aprotic organic solvents,a new sensing mechanism based on fluoride ion and water induced tautomerism of naphthalimide has been explored.In the process of fluoride ion sensing,the probe showed a significant absorption peak centered at 560 nm in the visible light range from 400 to 700 nm,and the peak change from 340 nm to 560 nm reached220 nm.When fluoride ion was added,the colorless probe solution immediately turns light purple;while there was a trace amount of water,the solution of the probe complexed with fluoride ion turned from purple to colorless;the sensitive color change of the fluoride ion complex was also used for fingerprint imaging.The significant change of DEPT135,~1H NMR and Infrared Spectroscopy confirmed that the structural transformation of the probe with high contrast.In addition,this work also proposed a probe sensitivity optimization strategy that based on adjusting tautomerism.Chapter 4:In this chapter,a series of enol-keto tautomers were designed and two compounds MBPM and BPM were synthesized.The tautomers were controlled by changing external conditions(such as solvent polarity).However,two compounds both exhibited stable properties,it was speculated that the electron-withdrawing ability of malononitrile group is so strong that lock the molecule,thus the malononitrile group should be replaced by a group with moderate electron-withdrawing ability.The reaction with 4-bromo-2-fluorophenoxy benzonitrile as a raw material can obtain the pure intermediate 3-Br XO.The nest step that reaction conditions should be more extensive screening or directly change the substituent grooups.In addition,this work also proposed a general strategy for the design of tautomeric molecular switches based on long-range proton transfer.Chapter 5:A more novel and versatile chemical sensor in structure and function was developed,and a powerful and adaptable 1,8-naphthalimide structure platform was planned to establish,which provided a bright prospect for 1,8-naphthalimide fluorophore in the field of fluorescence sensing,and a broader research direction for the application of 1,8-naphthalimide derivatives was also provided.It was expected to realize the long-range proton transfer and obtain high-contrast molecular switches,therefore a general strategy for the design of long-range tautomeric molecular switches could be formed,the photophysical proformance of long-range tautomeric molecular switches can also be regulated through multiple triggers.