Construction of Interlayer Conjugated Links in 2D Covalent Organic Frameworks via Topological Polymerization

Two-dimensional
covalent organic frameworks (2D COFs) are well-defined
polymeric sheets that usually stack in an eclipsed mode via van der
Waals forces. Extensive efforts have been made to manipulate interlayer
interactions, yet there still lack a way to construct conjugated connections
between adjacent layers, which is important for (opto)­electronic-related
applications. Herein, we report an interlayer topological polymerization
strategy to transform the well-organized diacetylene columnar arrays
in three different 2D COFs (TAPFY-COF, TAPB-COF, and TAPP-COF) into
conjugated enyne chains upon heating in the solid state. The resultant
COFs (COF-P) with retained high crystallinity possess broadened absorption
bands and narrowed band gaps. The newly formed conjugated chains provide
extra charge carrier pathways through direct π-electron delocalization.
As a proof-of-concept, after topological polymerization, the conductivity
of the TAPFY-COF film achieves 2.8 × 10–4 S/cm
without doping, and the photothermal, photoacoustic, and oxygen reduction
catalytic performance of TAPP-COF is significantly improved.