Zinc Porphyrin-based Covalent Organic Framework and Conjugated Microporous Polymer as Heterogeneous Photocatalysts for Reversible Addition-fragmentation Chain Transfer Polymerization

Zinc porphyrin-based covalent organic framework (COF) DhaTph-Zn-COF and conjugated microporous polymer (CMP) DhaTph-Zn-CMP as heterogeneous photocatalysts were prepared to activate photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization under broad-range wavelengths. They could efficiently transfer electrons to chain transfer agents to synthesize polyacrylamides and polyacrylates with controllable molecular weight, narrow molecular weight distribution (<1.20), and high chainend fidelity. The apparent polymerization rate constants were 0.0522 h(-1) and 0.0621 h(-1) for polymerization of N, N-dimethacrylamide with 2.5 mg/ mL DhaTph-Zn-COF or DhaTph-Zn- CMP, respectively, under yellow light irradiation. The different stacking patterns and the degree of conjugation for the freshly prepared COF and CMP materials affected structure and photophysical properties, such as crystallinity, specific surface area, band gap, fluorescence lifetime, charge transfer resistance, etc. Although DhaTph-Zn-COF had an ordered stacking with better electron transfer properties, their similar catalytic properties indicated that the stacking patterns were not the primary factor to enhance the performance of photocatalysts. Meanwhile, the difference in photocatalytic polymerization of metalloporphyrin-based COFs displayed that a building block (zinc porphyrin) with high photocatalytic efficiency in a homogenous system is vital to the design of the heterogeneous photocatalysts for polymerization. Besides, the stability of photocatalysts directly affected the efficiency of catalytic cycles. Compared with DhaTph-Zn-COF, the amorphous DhaTph- Zn- CMP showed more robust chemical stability after several rounds of polymerization and could be used at least five times. The reduced efficiency of DhaTph-Zn-COF after recycling resulted from the loss of active components. The scanning electron microscopy (SEM) revealed the morphological difference between the COF and CMP photocatalysts. Better stability could be credited to the tightpacked particles formed by the disorderly stacked structure, which avoided the destruction by external factors such as monomers, solvents, and stir. This work provides insights into the design factors of heterogeneous POP photocatalysts for photopolymerization and promotes the development of efficient semiconductors and heterogeneous photocatalysts. [GRAPHICS] .