Covalent Organic Frameworks as Favorable Constructs for Photodynamic Therapy

Covalent organic frameworks (COFs) with 2D pi-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 m(2) 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 mu g 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.