Construction Of Oxanthrace-like Dyes And Their Applications In Fluorescent Probes Based On π-conjugated System

Due to its excellent photophysical properties such as high molar extinction coefficient,high fluorescence quantum yield,high light stability,relatively long emission wavelength and good biocompatibility,oxanthracene dyes have attracted extensive attention from researchers.However,the absorption and emission wavelengths of traditional oxanthracene dyes are still in the ultraviolet/visible range（green to yellow）,and the Stokes shift（less than 30 nm）is too narrow,making it difficult to directly use them for target molecular detection and fluorescence imaging in living cells and animals.Therefore,it is of great importance for bioimaging applications to explore new strategies for developing long wavelength（greater than600 nm）oxanthracene dyes with excellent photophysical properties and large Stokes shifts.In this paper,aiming at the defects of traditional oxanthracene dyes,the structure modification of oxanthracene skeletons was carried out by means of fluorophobe fusion and changing the electron-absorbing groups to expandπ-conjugated system,hoping to obtain a series of fluorescent dyes with long wavelength emission（greater than 650 nm）and large Stokes shift（greater than 100nm）.The main work contents are as follows:Naphthalimide derivatives have the following characteristics of molecular structure:large conjugated system,common plane,one end of the molecule contains a strong electron-donating group,so naphthalimide compounds have been widely reported.The spectral characteristics of these compounds can be directly affected by the change of substituent groups at the 3/4-position.while the change of substituent group at 4-N atom has direct effect on the spectral characteristics of this compound.In this chapter,compounds 2a、2b、1a and 1b with large Stokes shift and long fluorescence emission wavelength were synthesized by modifying the substituents to synthesize 3-hydroxyl and 4-hydroxyl organic intermediates.On the basis of dye 1a,Hg²⁺probe Ra was obtained by using the"OFF-ON"mechanism of helicoid.The probe not only can specifically identify the target substance with high sensitivity,but also has low cytotoxicity and good membrane permeability。Oxanthracene dyes 1a and 2a synthesized by naphthalimide fluorophore fusion have the disadvantages of emission wavelength lower than 650 nm and weak fluorescence intensity Therefore,we intend to synthesize another new class of oxanthracene dyes Rb series by introducing electron donating/absorbing groups,and study their photochemical and physical properties.Compared with Rb1、Rb2、and Rb3,it is found that Rb4 has more excellent photochemical and physical properties.Moreover,the special structure of benzopyran can be used as the reaction site of Cl O^-,and the fluorescence quenching probe Rb4 can be constructed.The probe has the advantages of strong specificity,anti-interference,low detection limit and sensitive response for the detection of HCl O.Probe Rb4 can be used for selective determination of HCl O in CH₃OH/H₂O（9/1,v/v）system,but it is a fluorescently quenched fluorescence probe,which is easily interfered by background and other accidental factors.Therefore,we proposed a ratio fluorescent probe Rc with naphthalimide as fluorophore and benzopyran as reaction site to detect the emission shift of HCl O.In the presence of HCl O,the red fluorescence emission peak at 655 nm decreases significantly,and the blue fluorescence emission peak appears obviously at 462 nm.It can be seen that there is an emission shift of 193 nm between the two emission peaks,which is conducive to accurately measuring their intensity and ratio fluorescence peaks.More importantly,the probe Rc also shows high selectivity,good sensitivity,and is suitable for physiological conditions for the detection of HClO.And has been successfully used in strip and cell imaging.