Rapid, Scalable Construction of Highly Crystalline Acylhydrazone Two-Dimensional Covalent Organic Frameworks via Dipole-Induced Antiparallel Stacking

Covalent organic frameworks are an
emerging class of porous crystalline
organic materials that can be designed and synthesized from the bottom
up. Despite progress made in synthesizing COFs of diverse topologies,
the synthesis methods are often tedious and unscalable, hampering
practical applications. Herein, we demonstrate a scalable, robust
method of producing highly crystalline acylhydrazone two-dimensional
(2D) COFs with diversified structures (six examples) under open and
stirred conditions, with growth typically completed in only 30 min.
Our strategy involves selecting molecular building blocks that have
bond dipole moments with spatial orientations that favor antiparallel
stacking and whose structure allows the restriction of intramolecular
bond rotation (RIR) via intra- and interlayer hydrogen bonding. This
method is widely applicable for hydrazide linkers containing various
side-chain functionalities and topicities. By this strategy, the gram-scale
synthesis of two highly crystalline COFs (up to 1.4 g yield) was obtained
in a one-pot reaction within 30 min.