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 = H-2, 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 (lambda > 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.