Covalent Organic Frameworks as Favorable Constructs for Photodynamic Therapy

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.