High‐Efficiency Organic Semiconducting Small Molecule for Deep‐Tissue Phototheranostics: Single 1064 nm Laser Triggered NIR‐IIb Fluorescence Imaging Guided Type‐I Photodynamic/Photothermal Combination Therapy

Abstract Organic semiconducting small molecules that simultaneously possess NIR‐IIb (1500–1700 nm) fluorescence imaging (FLI), hypoxia‐tolerant photodynamic therapy (PDT) as well as photothermal therapy (PTT) abilities activated by a single NIR‐II (1000‐1700 nm) light can achieve high‐performance deep‐tissue phototheranostics, but have not gain much attention. Herein, a novel organic semiconducting small molecule (DTT) with an absorption maximum at 844 nm and an emission maximum at 944 nm in its monomer state is synthesized through delicate molecular design. Surprisingly, the emission spectrum of DTT can extend into NIR‐IIb region. Subsequently, phototheranostic nanoparticles (DTT NPs) with a dramatically red‐shifted maximum absorption/emission peak (1029/1128 nm) are skillfully developed based on the J ‐aggregation strategy, which show a greatly high molar absorptivity in NIR‐II region. Upon 1064 nm excitation, high resolution NIR‐IIb FLI can be achieved in whole‐body vessels, cerebral vasculatures, and tumors of living mice treated with DTT NPs. Moreover, DTT NPs can also produce type‐I reactive oxygen species and hyperthermia under 1064 nm laser irradiation for oxygen‐less‐dependent type‐I PDT and PTT combination therapy, eventually achieving efficient antitumor effects. This work provides a facile strategy of designing high‐efficiency small molecules for deep‐tissue phototheranostics.