Synthesis And Fluorescence Properties Of Novel Naphthimide Derivatives And Rhodamine B-based Small Molecule Fluorescent Probes

In organisms,hydrogen sulfide（H₂S）is the third important gas signal molecule,and its abnormal content is closely related to a variety of diseases;maintaining pH stability is also essential for the survival of all organisms,such as acidity is considered the main cause of cancer.Therefore,the fluorescence recognition and quantitative detection of H₂S and H⁺in organisms and in the environment is undoubtedly of great significance.In order to distinguish H₂S and H⁺by high-selectivity and high-sensitivity fluorescence,1,8-Naphthimide with high fluorescence quantum yield,large stockes shift,and stable optical performance,and Rhodamine B with large fluorescence emission wavelength,based on a certain fluorescence recognition mechanism,which is sensitive to acidity.By modifying them at the same or different positions and using different functional groups,two types of fluorescent probes with new structures and modification methods were designed and synthesized.Among them,Contains 5 1,8-Naphthimide fluorescent probes and 2 Rhodamine B colorimetric pH fluorescent probes.The specific research results are as follows:1、Naphthimide fluorescent probe for fluorescence recognition of H₂S1.Naphthimide fluorescent probe containing ebselenThe 4th position of 1,8-Naphthimide was modified with aminoethylamino,and then reacted with 2-chloroselenoyl benzoyl chloride to construct ebselen in the molecule through cyclization to obtain the target probe EPNF.Using the dual nucleophilic properties of H₂S,the（-Se-N-）bond in the ebselen structure is used as the recognition site.Through UV absorption and fluorescence emission spectroscopy,EPNF hasλex=425 nm andλem=521nm,and the excellent photophysical properties:high fluorescence quantum yield（0.6232）,large Stockes shift（96 nm）,which is fluorescence Identifying H₂S has laid an important foundation.EPNF can highly select fluorescence to recognize H₂S.When EPNF is added to H₂S,the emission peak blue shifts to 460 nm,a significant"turn-on"phenomenon occurs,and H₂S can be identified by high-selective fluorescence.The fluorescence recognition response is fast and sensitive（60 s）,and the applicable pH range is large（6～10）Strong anti-interference,the detection limit of H₂S is as low as 2.3μM.When EPNF is added to H2S,the color changes from yellow-green to bright green,enabling naked eye identification.The study also found that EPNF can be applied to the qualitative and quantitative fluorescence detection of H₂S in actual water samples;it has low cytotoxicity and can be used to identify and detect H₂S in living cells.2.Naphthalimide fluorescent probe containing selenoether bond（-Se-Se-）The 4th position of 1,8-Naphthimide was modified with a hydroxyl group,and then it was reacted with dibenzoyl chloride containing selenoether bond（-Se-Se-）to construct dinaphthoyl chloride in the same molecule the water-soluble target probe DSNF.The high reactivity of the selenoether bond（-Se-Se-）is used as a recognition site,and the ester bond generated by the connection of the phenolic hydroxyl group is used as the double recognition site.UV-vis and fluorescence emission spectra:λ_ex=469 nm andλ_em=545 nm.and the excellent photophysical properties:high fluorescence quantum yield（0.4234）,large Stockes shift（76 nm）,H₂S during identification,the emission peak intensity is significantly enhanced,and a significant"turn-on"effect is produced,with an increase of up to 10 times,The fluorescence recognition response is fast and sensitive（50 s）,the applicable pH range is large（6～10）,the anti-interference is strong,and the detection limit of H₂S is 0.54μM.The application of Hela cells found that it has low toxicity and has been successfully applied to the fluorescence recognition of H₂S in living cells,can be applied to the qualitative and quantitative fluorescence detection of H₂S in actual water samples.3.Benzimidazole naphthalimide fluorescent probe modified with azido at position 4The 4-bromo-1,8-naphthoic anhydride and o-phenylenediamine were cyclized to obtain a four-membered ring naphthalimide N2,and the 4th position was modified with an azide group to synthesize a new fluorescent probe DBNG.The azido group is easily reduced by H₂S,and it is used as a reaction site.Through UV-vis and fluorescence spectroscopy,the recognition of H₂S fluorescence by DBNG was explored.The experiment found thatλ_ex=450 nm andλ_em=515 nm of DBNG.When DBNG is added to H₂S,the fluorescence quantum yield changed from 0.1258 to 0.3689.DBNG can recognize H₂S with high selection and rapid fluorescence,and can realize naked eye recognition,resulting in a"turn-on"phenomenon and red shift,with a detection limit is 0.82μM.The electrostatic potential and HOMO and LUMO energy levels of the probe molecules are calculated by density functional theory,and the calculation results are consistent with the experiment.DBNG is used in qualitative and quantitative identification and detection of H₂S and cell fluorescence imaging in actual water samples.2、Novel pH fluorescent probe1.Fluorescent probe based on salicylaldehyde Schiff base naphthalimideUsing 3-aldehyde-4-hydroxy-1,8-naphthimide as the parent,through its aldehyde group to construct-C=N-NH-bond,respectively introduce 2-hydrazino-5-（p-chlorophenyl）-1,3,4-thiadiazole and 2-hydrazinobenzothiazole,designed and synthesized two salicylaldehyde-like Schiff base fluorescent probes XNFL（1-2）.All have a wide range of pH response changes.Accompanied by protonation under acidic conditions（pH=1～7）,it exhibits blue shift of absorption and emission spectra,with excellent linear relationship and blue-green fluorescence;under weak alkaline（pH=7～10）environment Along with deprotonation,bright yellow fluorescence appears after red shift;when pH>11,yellow-green fluorescence appears after blue shift.When pH value increases from 7 to 10,ratio response is obtained（Big Stoke Shift）,acidic and basic can be distinguished by the obvious spectral shift of the maximum absorption wavelength from 520 nm to 590 nm.In the density functional theory calculation,the energy band gap is reduced,which is consistent with the experimental results,which verifies the rationality of the target molecular structure.2.Ebselen-modified Rhodamine Type B Fluorescent ProbeUsing rhodamine B as the fluorophore,the ebselen ring was constructed through the amino groups of ethylenediamine and hydrazine hydrate respectively,and two pH fluorescent probes HLEQ（1-2）were designed and synthesized.The spiro ring structure of rhodamine B has the characteristics of colorless and non-fluorescence.Under certain acidic conditions,the ring can be opened to form a quinone form with pink fluorescence,achieving the purpose of fluorescence recognition of H⁺.The probe has excellent photophysical properties:under strong acid conditions,its fluorescence quantum yields have changed greatly（from 0.0334 to0.4234,and from 0.0342 to 0.5234）,and both can recognize H⁺by fluorescence with high selectivity and produce significant"Turn-on"phenomenon,in the range of pH=1.53～6.20,there is a good linear relationship between fluorescence intensity and pH,p Ka_（HLEQ-1）=3.42（±0.07）,p Ka_（HLEQ-2）=3.78（±0.07）,strong anti-interference,can be recognized by the naked eye,the probe is reversible in the acid/weak alkaline transition.Through density functional theory calculations,it is known that the introduction of ebselen has changed the orbital energy level of the molecule,and the fluorescence signal has been successfully converted between rhodamine B and ebselen.The theoretical calculation results are consistent with the experimental results of spectral analysis.