Chemistry Reference
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Fig. 3.2
Pore surface engineering in COFs.
a
The scheme shows a general strategy for surface
engineering of COFs through the combination of condensation reaction and click chemistry. In
the first step, COFs bearing azide units on the walls are synthesized by condensation reaction
of HHTP with azide-appended benzene diboronic acid (N
3
-BDBA) and benzene diboronic acid
(BDBA) in a designated molar ratio (
X
=
0-100 %). The content of N-appended wall units is
tunable from 0 to 100 %, depending on the molar ratio of N
3
-BDBA to BDBA. Five members of
X
%N
3
-COF-5 with different contents (
X
=
5, 25, 50, 75, and 100) were synthesized. The struc-
ture of 100%N
3
-COF-5 is shown in the figure, with all of the walls occupied by the N
3
-appended
phenylene units. In the next step, the azide groups on the COF walls are clicked with alkynes to
anchor various organic groups onto the walls of COFs (
X
%RTrz-COF-5). The density of surface
R groups on the walls is determined by the azide content in
X
%N
3
-COF-5.
b
Graphical represen-
tation of COF-5 upon surface engineering, which leads to the functionalization of organic groups
on the walls. The component, composition, and density of the organic groups on the walls are
controllable. Reprinted with permission from Macmillan Publishers Ltd.: Ref. [
3
], copyright 2011
was used in the synthesis procedures of COF-5 (Fig.
3.2
) and NiPc-COF. Through
controlling the azide compound content, a series of azide decorated COF-5 and
NiPc-COF products were obtained. The azide groups provided a favorable oppor-
tunity for the post-synthesis of COFs via effective click reaction. As a result,
introducing triazole-linked moieties into the channels of COF tuned the pore size
continuously. The designer successfully decorated COF-5 and NiPc-COF with dif-
ferent amounts (5, 25, 50, 75 and 100 %) of azide-decorated phenyl boronic acids.
Recently, Jiang et al. reported a synthetic strategy for constructing organocata-
lytic covalent organic frameworks via pore surface engineering [
4
]. Alternatively,
the alkyne group was introduced into the original materials with varied molar
ratios (Fig.
3.3
). Then the azide compound with pyrrolidine unit was utilized for
post-modification. The catalytic activity of the resulting product depends on the
density of the active sites on the pore walls.
