Novel NIR-Ⅱ Organic Fluorophores For Bioimaging Beyond 1550nm

In the past few years,the second near-infrared region molecular imaging（NIR-Ⅱ,1000-1700 nm）has become a powerful tool for cancer diagnosis and treatment.The organic small molecule fluorescent dye CH1055,reported in 2015 for NIR-Ⅱ bioimaging,opened a new era of small molecule imaging.NIR-Ⅱ imaging has a large penetration depth（up to 3 cm）,excellent temporal and spatial resolution（50 FPS,1mm）,and a high tumor-to-normal tissue ratio（T/NT）（up to 15）,In particular,NIR-Ⅱ fluorescence imaging in the 1500-1700 nm sub-window（NIR-Ⅱb）shows higher tissue penetration depth,resolution,and zero auto-fluorescence,and thus has superior bioimaging performance.So far,inorganic NIR-Ⅱb fluorophores,such as single-walled carbon nanotubes（SWNTs）,rare earth doped nanoparticles and quantum dots have been studied for biosensing and bioimaging above 1500 nm.However,due to the rare NIR-Ⅱb fluorophore skeleton and the very common aggregation-caused quenching（ACQ）effect,there are few reports on the organic small molecule NIR-Ⅱb fluorophores.In this study,the aggregation-induced emission（AIE）method was used to design and synthesize highly distorted NIR-Ⅱ small molecule fluorophores,such as HL3（45.5°in the S₀ state）,to extend its emission wavelength to the NIR-Ⅱb region.Fulthermore,in the water,the QY of HL3 dots in the NIR-Ⅱ window（>1000 nm）is 11.7%,and the QY in the NIR-Ⅱb region（>1550 nm）is 0.05%.In addition,for the first time,we used the NIR-Ⅱb dye HL3 dots with aggregation-induced emission（AIE）effect to achieve high-resolution in vivo imaging of blood vessels,cerebrovascular and lymphatic drainage dynamic process of the whole body at 1550 nm.The success of this project may continue to promote the development of small molecule NIR-Ⅱb fluorophores with a maximum emission wavelength of more than 1500 nm,so as to achieve biological imaging with higher penetration depth and temporal and spatial resolution.