Boron difluoride formazanate dye for high-efficiency NIR-Ⅱfluorescence imaging-guided cancer photothermal therapy

The small molecular second near-infrared(NIR-Ⅱ,1000-1700 nm)dye-based nanotheranostics can con-currently combine deep-tissue photodiagnosis with in situ phototherapy,which occupies a vital position in the early detection and precise treatment of tumors.However,the development of small molecular NIR-Ⅱ dyes is still challenging due to the limited electron acceptors and cumbersome synthetic routes.Herein,we report a novel molecular electron acceptor,boron difluoride formazanate(BDF).Based on BDF,a new small molecular NIR-Ⅱ dye BDF1005 is designed and synthesized with strong NIR-Ⅰ absorp-tion at 768 nm and bright NIR-Ⅱ peak emission at 1034 nm.In vitro and in vivo experiments demonstrate that BDF1005-based nanotheranostics can be applied for NIR-Ⅱ fluorescence imaging-guided photother-mal therapy of 4T1 tumor-bearing mice.Under 808 nm laser irradiation,tumor growth can be effectively inhibited.This work opens up a new road for the exploitation of NIR-Ⅱ small molecular dyes for cancer phototheranostics.