Synthesis And Photophysical Properties Of Furan-Containing Heterocycle-Fused BODIPY

Organic fluorescent dyes are rapidly developing in modern biomedicine and organic optoelectronic materials,among which NIR fluorescent dyes are widely used in biofluorescent imaging,photodynamic therapy（PDT）,sensors,environmental monitoring,molecular switches and photovoltaic cells due to their unique photophysical and photochemical properties.Therefore,the design and synthesis of NIR fluorescent dyes with high fluorescence quantum yields will not only provide small molecule fluorescent imaging and tracer reagents with better performance for modern biomedicine,but also have good potential for chemical biology and clinical testing and diagnostics.Fluoroboron dipyrrole（BODIPY）fluorescent dyes are an emerging class of dyes with excellent photophysical properties,which have been extensively investigated over the last two decades due to their high fluorescence quantum yields,high molar extinction coefficients as well as high single-linear oxygen yields and excellent photothermal stability.Functionalisation of the skeleton of the BODIPY core gives a range of derivatives for using in research areas such as bioscience and environmental monitoring.In this paper,the delocalization range of BODIPY molecules and the structural stiffness of BODIPY molecules was extended by the modification strategy of aromatic ring fusing,Furan-containing heterocycle-fused BODIPY molecules with high fluorescence quantum yield in the near infrared region were synthesized,and their photophysical properties and applications in biological imaging were systematically explored.The main content is as follows:（1）The synthesis of new heterocyclic system of furan-[3,2-e]-indole was explored.The important precursors of furan-[3,2-e]-indole molecules were successfully synthesized by using commercially available diphenylacetylene and 2-hydroxy-acetophenone as starting materials.A series of asymmetric BODIPY molecules were synthesized by this precursor and their photophysical properties were studied.It is found that the BODIPY molecules have good absorption and emission in common solvents.The maximum absorption wavelength can reach 668 nm,the maximum emission wavelength can reach 749 nm,and the maximum Stokes shift can reach 96 nm.Molar extinction coefficient is also large,up to 138000 cm^-1M^-1.With the increase of solvent polarity,the maximum absorption wavelength of the molecule has a small blue shift,and the maximum emission wavelength has a significant red shift.In addition,the series of compounds have excellent fluorescence properties and high fluorescence quantum yield,among which compounds 3-4 have a fluorescence quantum yield of 0.550 and a fluorescence lifetime of 3.19 ns and it decreases with the increase of solvent polarity.（2）An important precursor of benzofuran-[2,3-g]-indole was successfully synthesized by using the economically available dibenzofuran as the starting material,and then a series of asymmetric BODIPY molecules were synthesized,and the photophysical properties were studied.It is found that the BODIPY molecules have good absorption and emission in six common organic solvents.The maximum absorption wavelength can reach 644 nm,the maximum emission wavelength can reach 713 nm and the maximum Stokes shift can reach 102 nm.Molar extinction coefficient is also large,up to 126000 cm^-1M^-1.With the increase of solvent polarity,the maximum absorption wavelength of the molecule shifts blue and the maximum emission wavelength shifts red.In addition,the fluorescence properties of this series of compounds are excellent,with a high fluorescence quantum yield.The fluorescence quantum yield of compound 4-9 is up to 0.640,and the fluorescence lifetime of compound 4-9 is 3.90 ns,which decreases with the increase of solvent polarity.（3）The photophysical properties,molecular configuration,DFT calculation,cell imaging and lipid droplet specific imaging of benzothiophen-fused BODIPY molecules in the previous laboratory work were investigated.The maximum absorption and emission wavelengths of the BODIPY molecules are between 540 nm～700nm and 620 nm～780 nm.The red shift of the molecules is obvious after thickening and the Stokes shift is up to 88 nm.In addition,cell imaging showed that BODIPY 5-11 had high photostability and low cytotoxicity in living cells.