Selenadiazolesbenzothiadiazole‐Based Small Donor–Acceptor–Donor Dye for Photothermal Therapy in NIR‐II Window

Abstract Recently, photothermal therapy (PTT) has attracted enormous attention because of its low invasiveness, high spatiotemporal selectivity, and good therapeutic effect. Different types of photothermal conversion agents have been developed, particularly the second near‐infrared window (NIR‐II, 1000–1700 nm) organic small molecular dyes which have become an attractive research direction. Herein, a novel and simple donor–acceptor–donor (D–A–D) type NIR‐II dye SeC is designed and synthesized with 2λ4δ2‐[1,2,5]selenadiazolo[3,4‐f]‐2,1,3‐benzothiadiazole structure. To improve capability of SeC for biomedical applications, SeC molecules are encapsulated into DSPE‐PEG 2000 to construct nanoparticles SeC‐NPs, which show high photostability and biocompatibility. More importantly, SeC‐NPs exhibited an excellent photothermal performance and display high photothermal conversion efficiency (PCE) of 62% under 808 nm excitation. Because of favorable fluorescence property in NIR‐II window and high PCE, SeC‐NPs are successfully used for NIR‐II imaging and PTT of 4T1 tumor‐bearing mice models. In vivo studies demonstrate SeC‐NPs’ ability to suppress tumor growth under NIR photoirradiation without visible damage to main organs. Overall, this study develops a strategy to design a simple small molecule dye containing selenium for NIR‐II imaging, and SeC‐NPs shows high performance for PTT toward tumor.