Iminium-linked hyperporphyrin covalent organic framework mediates type I photodynamic therapy via a photoredox process.

Abstract

Most photosensitizers (PSs) mediate type II photodynamic therapy (PDT) via energy transfer to produce singlet oxygen. However, this mechanism is oxygen-dependent and less effective in hypoxic tumors. Type I PDT, which generates radical reactive oxygen species such as superoxide through electron transfer, is more hypoxia-tolerant, yet molecular design strategies remain limited. Herein, we report an iminium-linked hyperporphyrin covalent organic framework (IH-COF) that facilitates efficient type I PDT via a photoredox process. In a one-pot synthesis, trimethyloxonium tetrafluoroborate simultaneously quaternizes imine bonds to introduce electron acceptors and protonates porphyrins, red-shifting the Q-band to 725 nm via the hyperporphyrin effect. Mechanistic studies reveal that photoinduced electron transfer from hyperporphyrin units to iminium ions generates α-amino radicals, which reduce oxygen to superoxide while regenerating iminium ions. The oxidized hyperporphyrins are then reduced by biomolecules such as 1,4-dihydronicotinamide adenine dinucleotide, sustaining the photocatalytic cycle. Consequently, IH-COF exhibits excellent PDT performance under both normoxic and hypoxic conditions and elicits potent antitumor efficacy in colorectal and triple-negative breast cancer models in female mice. This study highlights the potential of COFs as versatile and biocompatible platforms for synergistic photomedicine applications.