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 macrocycles 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 (¹O₂), for efficiently killing tumor cells upon near-infrared light irradiation. Our first-principles calculations revealed that the observed high yield ¹O₂ 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.