Design And Application Of Fluorescent Probes Containing Cyanine Unit

Fluorescence probe detection method has the advantages of fast,convenient,high selectivity,high sensitivity and strong anti-interference ability.It has attracted more and more attention in the detection of heavy metal ions,amino acids and biothiols.Over the past few years,many fluorescent probes have been developed.However,these reported probes still have some problems.For example,the probe Stokes shift is small,short emission wavelength,poor selectivity.Therefore,it is necessary to design a new fluorescent probe with good fluorescence intensity and large Stokes shift.Cyanine fluorophore is a new type of fluorophore with unique conjugated skeleton,designable structure and ultra-high fluorescence quantum yield.However,the optical properties of cyanine probes still have some shortcomings,such as poor solubility and selectivity of target molecules,long response time and so on.Therefore,by modifying the side chain groups of the cyanine unit,optimizing and improving its optical detection ability still has a lot of room for development.Based on the above ideas,we take cyanine unit as the main research direction,structural modification of cyanine unit,design and synthesis of 17 new probes.Series A is a total of 5 probes prepared by the condensation reaction of indole derivatives and coumarin.B series are 4 reactive probes prepared by indole derivatives or isophorones and compounds with specific recognition sites.C series are a total of 8 probes prepared from indole derivatives and salicylaldehyde.All the synthesized probes were verified by ¹H NMR,¹³C NMR,IR,LC-MS to verify the correctness of the target compound structure,and a series of optical performance tests were performed on probes A3,B1,B2,B3,B4,C2.The specific selectivity of B1 and B4 to Ag⁺and Hg²⁺was tested in B series probes.Using Et OH as the detection solvent of the B1 probe,the B1 probe can specifically recognize Ag⁺and Hg²⁺by UV-visible absorption spectroscopy.In the probe solution containing Ag⁺and Hg²⁺,the UV absorption wavelength has a significant red shift and has no obvious response to other metal ions.Through fluorescence emission spectrum test,it can be found that probe B1 only has obvious selectivity to Hg²⁺,and its fluorescence intensity and wavelength change significantly.The response time of Hg²⁺was 5 min.The detection limit of Hg²⁺was 6.58μM.The synthesis of probe B4 is based on B1,and the maximum absorption wavelength can reach 661 nm to identify Ag⁺and Hg²⁺in the near infrared range.Probe B4has a highly sensitive recognition effect on Ag⁺and Hg²⁺in the solution of Et OH/H₂O=9:1.It can be found by the naked eye that the color of Ag⁺in probe B4 changes from orange to purple and the color of Hg²⁺solution changes from orange to dark purple.UV-visible absorption spectra showed that the maximum absorption wavelengths of Ag⁺and Hg²⁺were red-shifted to 533 nm and 535 nm,respectively,and the fluorescence intensity in the fluorescence emission spectrum was also significantly different from other metal ions.In addition,the response time of probe B4 to Hg²⁺is short and can be detected within 1 min,and the response time to Ag⁺is 10 min.Probe B4 has a wide p H detection range and can specifically detect Hg²⁺in the range of p H=1-11.Finally,the detection mechanism of B4probe for Hg²⁺and Ag⁺was verified by ¹H NMR and HPLC.Probe B2 and probe B3 tested the selective recognition of amino acids.Among them,B2probe can selectively recognize Cys and Glu in the solution of Et OH/H₂O=9:1,which is sensitive to Cys.In the system containing Cys,the absorption peak of B2 probe in ultraviolet spectrum at 433 nm disappears,and the fluorescence intensity decreases in the fluorescence emission spectrum,which belongs to the fluorescence closed probe.The detection limit of probe B2 for Cys was 1.85μM,and the stability of probe B2 for detecting Cys at p H=1-14was tested.The spectral test showed that probe B2 could stably detect Cys at p H=1-10.Probe B3 can selectively recognize GSH in the solution of Et OH/H₂O=9:1.When GSH was added to the probe,the absorbance increased in the UV spectrum test,and the fluorescence intensity increased in the fluorescence spectrum test.Finally,we tested the UV response of A3 in A series of probes to p H changes.From the UV absorption spectrum can be found can be divided into four similar intervals,which corresponds to the naked eye to see.The color of the solution at p H=1-4 is yellowish,purple at p H=5-10,colorless at p H=11-12,and pink at p H=13-14.In addition,we also tested the UV changes of C2 in C series probes to p H.It was found that there was an absorption peak at460 nm at p H=1-7,and the color of the solution was light yellow.At p H=8-14,the absorption peak at 460 nm disappeared,and the color of the solution was colorless.