A pyrenetetrayl/phenanthroline-based one-dimensional covalent organic framework for metal-free photocatalytic organic conversion

Abstract

Covalent organic frameworks (COFs) are a new type of metal-free heterogeneous catalysts that have emerged recently and are often used in light-driven organic transformations. Nevertheless, the photocatalytic organic conversion is predominantly based on 2D or 3D topological structures, leaving the 1D topology of COFs relatively unexplored systematically in this field. Herein, a one-dimensional phenanthroline-based covalent organic framework, named PP-COF, was developed by combining 4,4′,4′′,4′′′-(1,3,6,8-pyrenetetrayl)tetrakis[benzenamine] (PTBA) and 4,4′-(1,10-phenanthroline-2,9-diyl)bis[benzaldehyde] (PBBA). The prepared PP-COF not only possesses a high crystallinity, and remarkable stability, but also exhibits excellent light absorption capabilities within the visible-light range and favorable photoelectric response characteristics, compared to 2D PyTTA-COF. PP-COF can efficiently convert O₂ to ¹O₂ and O₂˙⁻ by exposure to air and visible light. This in turn facilitates photocatalytic indole functionalization and oxidative thiol coupling to yield bisaryl indoles and disulfides in yields ranging from moderate to high, respectively. Furthermore, the PP-COF exhibits excellent recyclability. This study proposes that the potential for light-induced organic conversion is promising in one-dimensional linear covalent organic frameworks.