Halogen Regulation in Vinylene-Linked Covalent Organic Frameworks for Efficient Photocatalytic C–H Thiolation of Quinone Derivatives

Abstract

Vinylene-linked covalent organic frameworks (COFs) are considered promising heterogeneous photocatalyst candidates for organic synthesis because of their robust and conjugated frameworks. For the first time, a series of vinylene-linked COFs decorated by halogen atoms (F, Cl, and Br) were synthesized and further utilized as photocatalysts for C−H activation reactions. The corresponding optoelectronic properties could be precisely regulated via the modulation of halogen functionalities in the nanopore channel of COFs. It is worth noting that the unique structures and optoelectronic properties make these COFs effective photocatalysts for C−H activation reactions in organic synthesis. All of the COFs exhibited extraordinary catalytic performance and reusability in C−H functionalization based on halogen functionalities. Especially, the highest yield was achieved in the photocatalytic C−H thiolation of 1,4-naphthoquinones with Br-COF photocatalyst because of the suitable conduction band position. This work may provide a new scaffold to rationally design vinylene-linked COFs as efficient photocatalysts in organic synthesis.

Ionization-triggered low exciton binding energy in covalent organic frameworks for efficient photocatalytic synthesis of benzimidazole

“…8–12 In contrast to traditional metal-based inorganic semiconductors, COFs possess well-defined and modular frameworks that permit precise manipulation of their optoelectronic characteristics at the molecular level by incorporating specifically designed building blocks, exploring novel linkages, and controlling the stacking modes, thus providing a perfect platform for investigating the underlying structure–activity relationship. 13–17 However, the widespread utilization of COFs in photocatalytic organic transformations is plagued by their high exciton dissociation energy ( E b ), which usually exceeds 100 meV and is much higher than those of inorganic semiconductors. 18–23 It is known that E b is defined as the strength of coulombic interaction of bound electron–hole pairs, and the lower E b is, the easier it is to generate free charge carriers.…”