Synthesis And Imaging Properties Of Long Wavelength Dyes Based On Xanthene

Due to their excellent photophysical properties,such as high molar extinction coefficient,high fluorescence quantum yield,high photostability,relatively long emission wavelength and good biocompatibility,xanthene dyes have received extensive attention.However,the conventional xanthene dyes have short emission wavelengths(green to yellow)and narrow Stokes shifts(<30 nm),which can generally results in photo-damage and self-quenching due to back scattering from biological samples.Therefore,exploring new design strategies to develope long-wavelength(>600 nm)xanthene dyes with excellent photophysical properties and large Stokes shifts is of great importance for their bioimaging applications.In this paper,a series of dyes with long wavelength emission(>600 nm)and large Stokes shifts(>30 nm)ere synthesized by using three different strategies to modify the xanthene skeleton.Meanwhile,the organelle-targeting labeling of dyes/probes is achieved without introducing additional targeting groups.The main works are as follows:Fluorescent dyes RQ and JRQ with emission wavelengths(>650 nm)and large Stokes shifts(>76 nm)were constructed by introducing the electron-donating group4-diethyl-1,2,3,4-tetrahydroquinoxaline to change the intramolecular charge transfer(ICT)properties of xanthenes.Since RQ and JRQ possessed the unique spirocyclic/open-ring process of xanthenes that could be employed as an effective platform in constructing fluorescence turn-on sensors,thus,RQS,RQNN,JRQN and JRQNS were constructed.As expected,all probes exhibited multiple excellent properties,such as high selectivity,high sensitivity,fast response time,low cytotoxicity and good membrane permeability.Importantly,the dyes(RQ and JRQ)and probes(RQS,JRQN and JRQNS)can precisely target the mitochondria without introducing additional localization groups.A series of probes(MXS,MXSO,MXAC and MXNS)with long wavelength emission(630–654 nm)and large Stokes shifts(80–130 nm)were obtained by using the xanthene 9-position modification,and systematically explored the recognition performance and cell imaging application.Surprisingly,by simply fusing a carbon-carbon double bond in the conventional xanthene,probes can effectively increase the emission wavelength and Stokes shifts.A novel mitochondria-targeted fluorescent probe MXSO based on a fluorescent rotatable xanthene-hemicyanine dyad for the detection of the viscosity has been successfully synthesized.MXAC,a lysosome-targeted fluorescent probe was developed for discrimination of Cys over GSH/Hcy based on a specific 1,2-addition reaction,in which the carbon-carbon double bond located at N,N-diethyl.4-(N,N-(bis-(2-hydroxyethylthioethyl))benzaldehyde)unit was selected as the recognition group and electron donor,3-diethylamino-6-methoxy-9-methylxanthine unit was selected as fluorophore and electron acceptor to synthesize a ratiometric Pd²⁺fluorescent probe MXNS.As expected,MXNS is cell-membrane permeable and mitochondria-targetable,and can be used for monitoring mitochondrial Pd²⁺in the living cell.A series of novel?-extended xanthene dye(RQN)and probes(RQNS,RQNA and RBSO)with long emissive wavelengths(647–686 nm)and larger Stokes shifts(55–86 nm)were respectively prepared via an intramolecular nucleophilic substitution of aromatic hydrogen(S_NAr^H)strategy.As expected,RQN displayed excellent properties and was capable of specifically distributing in lysosome.RQNA exhibited a high selectivity,high sensitivity,and fast response time for the detection of Cu²⁺via a specific Cu²⁺-triggered ring-opening and hydrolysis cascade reaction.RQNA is cell-membrane permeable and mitochondria-targetable,and can be used for monitoring mitochondrial Cu²⁺in the living cell.A novel mitochondria-targeted fluorescent probe RQNS for the detection of the HCl O has been successfully synthesized.A novel lysosome-targeted fluorescent probe RBSO was developed for imaging Msr A in living cells based on ICT mechanism,exhibiting long emission wavelength(684 nm),high selectivity,rapid response time(8 min).