Furan Donor for NIR-II Molecular Fluorophores with Enhanced Bioimaging Performance

The second near-infrared(NIR-II,1,000 to 1,700 nm)molecular fluorophores containing donor–acceptor–donor conjugated backbone have attracted substantial attention due to their outstanding advantages,such as stable emission and facilely tuned photophysical properties.However,it is still challenging for them to simultaneously achieve high brightness and red-shifted absorption and emission.Herein,furan is adopted as the D unit to construct NIR-II fluorophores,demonstrating red shift of absorption,enhanced absorption coefficient,and fluorescent quantum yield when compared with the generally used thiophene counterparts.The high brightness and desirable pharmacokinetics of the optimized fluorophore,IR-FFCHP,endows improved performance for angiography and tumor-targeting imaging.Furthermore,dual-NIR-II imaging of tumor and sentinel lymph nodes(LNs)has been achieved with IR-FFCHP and PbS/CdS quantum dots,enabling the in vivo imaging navigated LN surgery in tumor-bearing mice.This work demonstrates the potential of furan for constructing bright NIR-II fluorophores for biological imaging.

High brightness NIR-Ⅱ nanofluorophores based on fused-ring acceptor molecules

It is challenging to develop molecular fluorophores in the second near-infrared(NIR-Ⅱ)window with long wavelength emission and high brightness,which can improve the performance of biological imaging.Herein,we report a molecular engineering approach to afford NIR-Ⅱ fluorophores with these merits based on fused-ring acceptor(FRA)molecules.Dioctyl 3,4-propylenedioxy thiophene(PDOT-C8)is utilized as the bridging donor to replace 3-ethylhexyloxy thiophene(3-EHOT),leading to more than 20 times enhancement of brightness.The nanofluorophores(NFs)based on the optimized CPTIC-4F molecule exhibit an emission peak of 1,110 nm with a fluorescence quantum yield(QY)of 0.39%(QY of IR-26 is 0.050%in dichloroethane as reference)and peak absorption coefficient of 14.5 x 10^4 M^-1·cm^-1 in aqueous solutions,which are significantly higher than those of 3-EHOT based COTIC-4F NFs.It is found that PDOT-C8 can weaken intermolecular aggregation,enhance protection of molecular backbone from water,and decrease backbone distortion,beneficial for the high brightness.Compared with indocyanine green with same injection dose,CPTIC-4F NFs show 10 times higher signal-to-background ratio for whole body vessels imaging at 1,300 nm long pass filters.