Photoactive Donor–Acceptor Covalent Organic Framework Material for Synergistic Cyclization Approach to Imidazole Derivatives

Abstract

As one of the most potential platforms for heterogeneous catalysis, two-dimensional porphyrin-based covalent organic frameworks (COFs) have attracted great research interests. In this work, following the correlation of COF structure and their performance, a type of donor–acceptor 2D COF (Por-COF-Zn) based on porphyrin and thiophene units was designed and easily constructed by one-pot method using 5,10,15,20-tetra-(4-aminophenyl)porphyrin (TAPP), thieno[3,2-b]thiophene-2,5-dicarbaldehyde, and zinc acetate. The as-synthesized COF material is tested to show high crystallinity and good thermal and chemical stability. The Brunauer–Emmett–Teller (BET) measure results show that the specific surface area of Por-COF-Zn is 413.6 m²g⁻¹, and the pore volume is 0.279 cm³g⁻¹. Transient photocurrent response and EIS measurement also demonstrate that Por-COF-Zn exhibits an efficient separation of photogenerated electron/hole pairs. The photocatalytic performance of the resulted COF was further evaluated by using intramolecular cyclization of N-phenyl-o-phenylenediamine and benzaldehyde to form benzimidazole derivative. The catalyst system exhibited good to high conversion efficiency, moderate substrate applicability, and excellent stability and recyclability for the catalytic cyclization approach of benzimidazoles. The catalytic mechanism should be contributed to the synergistic effect of organic framework and metallic zinc. Our current work also provides valuable information for understanding COF-based photocatalytic systems and further highlight new insights to meet new challenges of heterogeneous photocatalysis.