A nanographene‐based two‐dimensional covalent organic framework as a stable and efficient photocatalyst

The bottom-up synthesis of covalent organic frameworks (COFs) with desirable organic units furnishes functional materials with unique structural and chemical properties. As an emerging class of two-dimensional (2D) COFs, sp2-carbon–conjugated COFs provide a facile platform with which to construct highly stable and crystalline porous polymers with intriguing photocatalytic efficiency. However, constructing COFs with high photoconductivity and charge-carrier mobility while maintaining a sufficient photoredox potential remains a considerable challenge. Herein, a 2D vinylene-linked COF was prepared by employing nanographene, namely, dibenzo[hi,st]ovalene (DBOV), as a building block. The resulting 2D DBOV-COF exhibits unique ABC-stacked lattices, enhanced chemical stability, and a charge-carrier mobility of ~0.6 cm2·V-1·s-1 inferred from ultrafast terahertz conductivity measurements. The ABC-stacking structure was unambiguously revealed by the high-resolution transmission electron microscopy, in addition to the powder X-ray diffraction. Notably, DBOV-COF demonstrated remarkably high photocatalytic activity in hydroxylation, which was attributed to the exposure of narrow-energy-gap DBOV cores as active sites in the COF pores, in conjunction with efficient charge transport following light absorption