NIR-II light-response porphyrin-heptazine-based conjugated organic polymers for highly efficient photooxidation†

Three novel porphyrin-heptazine-based conjugated organic polymers (MTPP-Cys, M = H₂, Ni, Cu) have been constructed, and an intramolecular donor–acceptor (D–A) structure has been formed by the electron-rich porphyrin and electron-deficient s-heptazine. Benefitting from the excellent light-absorbing potential of porphyrin, and significantly enhanced intramolecular charge transfer caused by directly linked porphyrin and s-heptazine, the synthesized polymers present prominent sunlight absorption even up to 1800 nm. Compared to the graphitic carbon nitride (g-C₃N₄), MTPP-Cys all show a superior photooxidation capability of 1,4-dihydro-2,6-dimethylpyridine-3,5-dicarboxylate (1,4-DHP) under irradiation with a xenon lamp (λ > 420 nm). Notably, H₂TPP-Cy synthesized using free-base porphyrin and s-heptazine shows more than 33 times higher photooxidation efficiency than g-C₃N₄. When masking visible-light, instead of no catalytic activity with g-C₃N₄ or porphyrin monomers, MTPP-Cys can still guarantee highly efficient conversion of 1,4-DHP with only a slightly extended reaction time. This investigation will provide a new idea about reasonable design and construction of novel heptazine-based D–A type conjugated organic polymers with efficient photocatalytic performance.