Two-Dimensional Fully Conjugated Polymeric Photosensitizers for Advanced Photodynamic Therapy

Photodynamic therapy (PDT) is attractive for treatment of various cancers, with a high selectivity, minimal long-term effect, and excellent cosmetic appeal. Well water-dispersive photosensitizers with strong optical absorption within the tissue transparency window (700-1000 nm) are needed for efficient PDT. However, clinically used PDT agents based on oligomeric porphyrin units (e.g., protoporphyrin IX) are effective at 532 nm irradiation only. Herein, we synthesized a two-dimensional covalent organic polymer (COP) containing fully conjugated multiple porphyrin macrocydes with sulfonic acid side groups. The resultant COP-P-SO3H is well water-dispersive, showing strong optical absorption within the desired therapeutic window and a high quantum yield of reactive oxygen species, especially singlet oxygen (O-1(2)), for efficiently killing tumor cells upon near-infrared light irradiation. Our first-principles calculations revealed that the observed high yield O-1(2) resulted from the unique side-on parallel diatomic adsorption (Yeager mode) of triplet oxygen molecules on the highly conjugated porphyrin rings in the photoexcited COP-P-SO3H.