Rationally Designed Benzobisthiadiazole-Based Covalent Organic Framework for High-performance NIR-II Fluorescence Imaging-guided Photodynamic Therapy.

Although being applied as photosensitizers for photodynamic therapy, covalent organic frameworks (COFs) fail the precise fluorescence imaging in vivo and phototherapy in deep-tissue, due to short excitation/emission wavelengths. Herein, we propose the first example of NIR-II emissive and benzobisthiadiazole-based COF-980. Comparing to its ligands, the structure of COF-980 could more efficiently reducing the energy gap (ΔE S1-T1 ) between the excited state and the triplet state to enhance photodynamic therapy efficiency. Importantly, COF-980 demonstrates high photostability, good anti-diffusion property, superior ROS generation efficiency, promising imaging ability and ROS production in deep tissue (ཞ8 mm). In vitro results reveal COF-980 combined with laser irradiation could trigger larger amount of intracellular ROS to high-efficiently induce cancer cell death. Notably, COF-980 NPs precisely enables PDT guided by NIR-II fluorescence imaging that effectively inhibit the 4T1 tumor growth with negligible adverse effects. This study provides a universal approach to developing long-wavelength emissive COFs and exploits its applications for biomedicine. This article is protected by copyright. All rights reserved.