Synthesis,Photophysical Properties And Application Of Carbocyanines Substituted By Formyl On The Methine Chain Methyl Chain

The unique D-?-A structure of cyanine dyes and their advantages in biology,photomedicine and analysis make people pay more attention to the research of cyanine dyes.The photophysical properties of cyanine dyes can be adjusted by modifying aromatic heterocycles,methine chain and substituents on heterocyclic nitrogen in the structural skeleton.Moreover,modification on methine chain can significantly change their photophysical properties and interactions with other molecules.Formyl is one of the most important functional group in organic chemistry,which has strong electrophilic property.It is not only a strong electron-withdrawing group,but also can form hydrogen bond with water molecule.In addition,there are few studies on the properties of formyl-substituted cyanines on the methine chain.Therefore,this paper studies the hydroformylation on the methine chain of asymmetric carbocyanines,and we synthesized carbocyanines substituted by formyl on methinel chain and investigated its photophysical properties and applications.The main research contents and results are as follows:1.The cyanine dyes modified on methine chain in recent years were reviewed,including their synthesis methods,spectral properties and biological applications.2.Five asymmetric carbocyanine dyes 3a-e and one formyl-substituted symmetric indole carbocyanine dye 4f were synthesized from various heterocyclic quaternary ammonium salts and Fischer aldehyde.The hydroformylation on the methine chain of 3a-e was investigated,and five new formyl-substituted asymmetric carbocyanine dyes 4a-e were synthesized in one step.The structures of the synthesized dyes were characterized by UV-vis,¹H NMR,¹³C NMR and HRMS.The possible formation mechanism of asymmetric carbocyanine dyes and various formyl-substituted carbocyanine dyes was proposed.3.The spectral properties of asymmetric carbocyanine dyes and carbocyanine dyes substituted by formyl on methine chain in different solvents were measured.The absorption spectra showed that the absorption maxima(?_max)of asymmetric carbocyanines3a-e and formyl-substituted carbocyanines 4a-f in methanol were in the range of 541-656nm and 487-610 nm,respectively.Compared with the corresponding parent 3a-e,the?_maxof 4a-e was blue-shifted 46-66 nm,and the?of 4a-e also decreased.Fluorescence spectra showed that the fluorescence intensity of carbocyanine with benzo[c,d]indole ring was lower than that with indole,benzothiazole and quinoline ring.Compared with 3a,3c and3e,the?_em of 4a,4c and 4e in 90%glycerol-water solution was blue-shifted 27 nm,31 nm and 25 nm,respectively,and their fluorescence intensity also decreased.Compared with the parent carbocyanines,the Stokes shift became larger after the formyl group was introduced into the methine chain.4.The photostability of carbocyanine dyes in PBS was determined.After irradiation for 1 h,formyl-substituted carbocyanine dyes 4a-f showed 2%,0.5%,1%,3%,1.5%and1.5%photofading respectively,while parent dyes 3a-e showed 5%,17%,57%,8%and 5%respectively.It was not easily oxidized and the stability was improved after the formyl group was introduced.5.The solubility of carbocyanine dyes in PBS was determined by spectroscopy.The results showed that the solubility of formyl-substituted carbocyanine dyes 4a,4b,4c,4d and 4e was 40,51,46,78 and 39 times that of parent dyes 3a,3b,3c,3d and 3e,respectively.The water solubility of carbocyanine dyes 4a-e was greatly improved after the formyl group was introduced.6.The interaction between formyl-substituted carbocyanine dyes and 13 anions was investigated.The results showed that formyl-substituted carbocyanines 4a-f had strong interaction with CN?.They could detect CN?quickly with high selectivity and could also recognize the existence of CN?by naked eyes according to the color change of solution.The detection limits of 4a-f for CN?were 0.91?M,0.46?M,0.53?M,1.15?M,0.75?M and 0.97?M,respectively.The mechanism of CN?detected by 4a was explored by UV-vis,¹H NMR,¹³C NMR and HRMS.The result showed that the mechanism was that CN?attacked the iminium cation of heterocyclic quaternary ammonium salt in 4a and reacted with D-?-A in 4a by a 1,2-nucleophilic addition reaction.