Design And Optimization Of NIR-? Molecular Fluorephores

Comparing with traditional visible?400-700 nm?and the first near-infrared?NIR-I,700-1000 nm?regions,biological imaging in the second near-infrared region?NIR-?,1000-1700 nm?has attracted a lot of attention due to its advantages of deeper tissue penetration and higher signal-to-noise ratio.The development of NIR? fluorophores plays an important role for the advance of NIR-? imaging.NIR-? molecular fluorophores are promising for clinical translation due to their good biocompatibility.However,the emission wavelength of the reported NIR-? molecular fluorophores needs to be further red-shifted and their absorption coefficients and fluorescence quantum yield?QY?should be simultaneously improved.Therefore,it is of great significance to explore NIR-? molecular fluorophores with required performance.The optical properties of molecular fluorophores are closely relevant to their structures and can be improved by rational molecule design.In this dissertation,NIR? molecular fluorophores with shielding unit-donor-acceptor-donor-shielding unit?S-D-A-D-S?structure and fused-ring acceptor?FRA?structure are developed by molecular engineering,and their nanofluorophores?NFs?were prepared by encapsulation with DSPE-m PEG2000 to enable aqueous solubility.For S-D-A-D-S molecules,their QYs were successfully improved by structural optimization of their donor units.For FRA molecules,simultaneously improved absorption coefficients and QYs were realized by structural optimization of their bridge donor units.The contents of this thesis are described as follows:In the first section,the fundamental information of NIR-? imaging is briefly introduced,including the advantages of NIR-? imaging and its development,the classification of NIR-? fluorophores and the development of molecular fluorophores.At the end,the aims and contents of this thesis are proposed.In the second section,experimental materials and methods are introduced,including experimental materials,experimental instruments,synthesis of molecular fluorophores,preparation of water-soluble NFs,the measurement of dynamic diameters of NFs,the measurement of absorption and emission spectra,the measurement of fluorophore stability,bio-imaging application,QY calculation and theoretical calculation methods.In the third section,donor engineering is applied on S-D-A-D-S fluorophores and the structure-optical property relationships are elucidated.Compared to n-FT with thiophene?T?as donor,n-FE with 3,4-ethylenedioxy thiophene?EDOT?as donor and n-FE346 with 3,3-dibutyl-3,4-propylenedioxy thiophene?PDOT-C4?as donor,the n-FES with 3,4-ethylenedithio thiophene?EDST?as donor shows the higher QY of 5.45%?Reference to IR-26 with QY of 0.05% in dichloroethane?in toluene.The fluorescence emission peaks of the four corresponding NFs are over 1040 nm in aqueous solutions.The QY of n-FES NFs is 1.25% in aqueous solutions,higher than 0.01% of n-FT NFs,0.27% of n-FE NFs,and 0.89% of n-FE346 NFs.The theoretical calculation results show that the backbone of n-FES is more distorted than the other three molecules due to the bulkier EDST donor,which weakens intermolecular aggregation in NFs and reduces fluorescence quenching,resulting in higher QY of n-FES than n-FT,n-FE and n-FE346.In the fourth section,the bridge donor units are engineered to improve the optical properties of fused-ring acceptor molecules.The corresponding water-soluble NFs exhibited emission peaks located at 1110 nm and large Stokes shift.Compared to COTIC-4F NFs and CBTIC-4F NFs with 3-??2-ethylhexyl?oxy?thiophene?3-EHOT?and 3-??2-butyloctyl?oxy?thiophene?3-BOOT?as bridge donors,respectively,CPTIC-4F NFs with 3,3-dioctyl-3,4-propylenedioxy thiophene?PDOT-C8?as bridge donor exhibits better optical performance with peak extinction coefficient of 14.5 × 104 M^-1cm^-1,QY of 0.39% and the brightness of 490?under 808 nm excitation?in phosphate buffer saline?PBS?,which is ranked among the highest brightness values of the reported NIR-? molecular fluorophores.Theoretical calculation and molecular dynamic simulations demonstrate that the higher aqueous brightness of CPTIC-4F NFs can be attributed to the enhanced protection of molecular backbone from water and decreased backbone distortion.