Bio‐Erasable Intermolecular Donor–Acceptor Interaction of Organic Semiconducting Nanoprobes for Activatable NIR‐II Fluorescence Imaging

Abstract Activatable second near‐infrared window (NIR‐II; 1.0–1.7 µm) fluorescence probes that uncage deep‐tissue penetrating fluorescence by disease‐related biomarker stimuli hold great promise for detecting diseases with a poor understanding of the pathology at the molecular level with unprecedented resolution. However, currently, very few activatable NIR‐II fluorescence probes are reported mainly due to the lack of a simple yet general design strategy. Herein, a new and fairly generic design strategy using a bio‐erasable intermolecular donor–acceptor interaction to construct activatable NIR‐II fluorescence probes is reported. An organic semiconducting nanoprobe (SPNP) is constructed through blending a biomarker‐sensitive organic semiconducting non‐fullerene acceptor (3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐cyclopentane‐1,3‐dione‐[c]thiophen))‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno[2,3‐d:2',3'‐d']‐s‐indaceno[1,2‐b:5,6‐b'] dithiophene) (ITTC) (one of electric acceptors in organic solar cells) with a biomarker‐inert semiconducting polymer donor 5‐(4,8‐bis((2‐ethylhexyl)oxy)‐6‐methylbenzo[1,2‐b:4,5‐b']difuran‐2‐yl)‐10‐methylnaphtho[1,2‐c:5,6‐c']bis([1,2,5]thiadiazole) (PDF) in an amphiphilic‐polymer‐coated single nanoparticle to suppress NIR‐II fluorescence of the donor via a intermolecular donor–acceptor interaction. The acceptor ITTC is found to be specifically degraded by hypochlorite (an important biomarker) to erase its acceptor property, thus erasing the intermolecular donor–acceptor interaction and uncaging NIR‐II fluorescence. Consequently, SPNP exhibits a 17.5‐fold higher fluorescence brightness in the hypochlorite‐abnormal inflammation in vivo than in normal tissues. Our bio‐erasable intermolecular donor–acceptor interaction strategy provides simple yet general guidelines to design various biomarker‐activatable NIR‐II fluorescence probes.