Covalent Organic Frameworks as Favorable Constructs for Photodynamic Therapy

Abstract Covalent organic frameworks (COFs) with 2D π‐conjugation were designed and synthesized as molecular photosensitizers for efficient photodynamic therapy. Two molecules, 5′,5′′′′‐(1,4‐phenylene)bis(([1,1′:3′,1′′‐terphenyl]‐4,4′′‐dicarbaldehyde)) (L‐3C) and 4,4′,4′′‐(1,4‐phenylene)bis(([2,2′:6′,2′′‐terpyridine]‐5,5′′‐dicarbaldehyde)) (L‐3N), inactive to generating reactive oxygen species (ROS), were linked to form two COFs, COF‐808 and COF‐909, respectively, exhibiting excellent ROS production efficiency. The high permanent porosity of these COFs (surface areas 2270 and 2610 m2 g−1) promoted diffusion of both oxygen and release of ROS in cells. This, combined with the excellent photostability and biocompatibility, led to excellent PDT performance. In vitro, over 80 % of tumor cells were killed after PDT treatment using COF‐909 at the concentration of 50 μg mL−1 for 150 s. In vivo, drastic reduction of tumor size was observed (from 9 mm to less than 1 mm) after 10 day treatment.