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ters centered at 1.4 nm and 1.9 nm. The positively charged
networks of the COFs were verified through zeta potential
analysis. By virtue of their well-defined ionic frameworks, the
as-synthesized COFs can be uniformly composited with
polyethylene oxide (PEO) and lithium bis(trifluoromethyl-
sulfonyl)imide (LiTFSI), displaying satisfactory lithium-ion
(Li-ion) conductivity.
COFs (Figure 3b). Further support of the structural inter-
pretation was obtained by comparison of spectroscopic data
of the model compound N-ethyl-2,4,6-tri[(E)-styryl]pyridi-
nium bromide with the COFs, which showed good accordance
(Figure 3a and b). Raman spectra analyses of the as-
synthesized COFs exhibit a band at ꢀ 1635 cmÀ1, indicative
=
of the formation of C C bonds (Supporting Information,
We used ETMP-Br and TFPT to prepare one of the COFs,
namely ivCOF-1-Br (Figure 2a). After a series of optimiza-
tions (Supporting Information, Table S1), the reaction was
performed by using dimethylamine as base catalyst in a mixed
solvent of N,N-dimethylformide and ortho-dichlorobenzene
with a 7:3 volume ratio at 1808C in a sealed tube for 3 days.
The precipitate generated by the process was collected
through filtration and washed with the organic solvents
acetone, methanol, and dichloromethane to afford a pale
yellow powder with an 87% yield. To verify the general-
izability of our synthesis strategy, another tritopic aromatic
aldehyde monomer with the extended spacer TFBT was used
for condensation with ETMP-Br under identical reaction
conditions (Figure 2a). The product ivCOF-2-Br was
obtained as a yellow powder with a yield of 91%.
The as-synthesized COFs were measured through powder
X-ray diffraction (PXRD). Four distinguishable diffraction
peaks at 2q = 5.78, 10.08, 15.38, and 25.98, corresponding to the
(100), (110), (210), and (001) planes, were found on the
PXRD pattern of ivCOF-1-Br, demonstrating its crystallinity
(Figure 2b). Its hexagonal lattice crystal structure was
modeled, and Pawley refinement was performed against the
experimental PXRD pattern. The results indicated that the
layered structure of ivCOF-1-Br was stacked along the c-axis
with slight slippage from the eclipsed configuration, in which
the ethyl group of pyridinium unit was oriented to different
directions with a 1208 angle between the adjacent COF layers
to avoid cationic pyridinium centers directly on top of each
other. The unit cell parameters were a = b = 17.84 ꢀ and c =
3.43 ꢀ, with good R-factors (Rp = 3.03%, Rwp = 3.79%). For
ivCOF-2-Br, four well-defined diffraction peaks at 2q = 4.08,
6.98, 7.98 and 10.68 corresponding to the (100), (110), (200)
and (210) planes were observed on the PXRD pattern
(Figure 2c). Its structure was also modeled with Pawley
refinement against its PXRD pattern, exhibiting a large
hexagonal lattice with similar stacking arrangement and unit
parameters of a = b = 25.60 ꢀ and c = 3.56 ꢀ with good R-
factors (Rp = 2.62%, Rwp = 3.44%).
Figure S2). Nitrogen 1s XPS analyses revealed a 3:1 ratio of
triazine N to pyridinium N, manifesting the monomers
reacted stoichiometrically to afford the COFs (Supporting
Information, Figure S3). In the thermogravimetry profiles,
the weight loss (approximately 7 wt.%) at low temperatures
(150 to 2508C) for ivCOF-1-Br was possibly due to the loss of
solvent molecules trapped in the pores (Supporting Informa-
tion, Figure S4). Substantial weight loss appeared until 5508C
for both COFs and was attributed to the decomposition of the
frameworks, indicating high thermal stability. The COFs also
showed highly chemical stability as evidenced by the intact
PXRD pattern after a two-week soaking in water, 14 M
NaOH or 12 M HCl aqueous solution (Supporting Informa-
tion, Figure S5). The as-synthesized COFs were nearly
quantitatively recovered after water treatment. Moreover,
upon the tests in 14 M NaOH or 12 M HCl aqueous solution,
the residue weight percentages of the COFs were achieved as
90–94 wt% or 95–97 wt%, respectively, which were compa-
rable to other olefin-linked COFs.[3f]
The nitrogen physisorption isotherms of the as-synthe-
sized COFs were measured at 77 K to assess their porosity.
Typical type I isotherms were observed for both COFs,
indicating the presence of sole micropores (Figure 3c and d).
The Brunauer–Emmett–Teller (BET) surface areas were 873
and 1343 m2 gÀ1 for ivCOF-1-Br and ivCOF-2-Br, respec-
tively. In accordance with the adsorption isotherms,
quenched-solid density functional theory (absorption
branch) based on the carbon model for cylindrical pores
was used to calculate the pore-size distribution, yielding
monodispersed pore diameters at 1.4 and 1.9 nm for ivCOF-1-
Br and ivCOF-2-Br, respectively (Figure 3c and d, inset). The
ionic natures of the as-synthesized COFs were characterized
through a zeta potential analysis. The zeta potential values of
10.59 mV (Æ 0.55 mV) and 18.13 mV (Æ 1.94 mV) for the
respective dispersions of ivCOF-1-Br and ivCOF-2-Br in
methanol indicated the positive charge of their skeletons. The
microstructures of the two COFs were ascertained through
scanning electron microscopy (SEM) and transmission elec-
tron microscopy (TEM) measurements. The ivCOF-1-Br was
composed of granular polycrystallites with 0.5–1 mm size,
whereas ivCOF-2-Br exhibited a fibrillar morphology with
100–500 nm length (Supporting Information, Figure S6). A
high-resolution TEM image of ivCOF-1-Br revealed a lattice
fringe of 1.46 nm corresponding to the (100) plane of the
hexagonal lattice (Figure 3e), which is in good accordance
with the simulated structure (Supporting Information, Fig-
ure S20).
The chemical structures of the two COFs were analyzed
by Fourier transform infrared spectroscopy and solid-state 13
C
cross-polarization magic-angle spinning nuclear magnetic
resonance (NMR) spectroscopy. As shown in Figure 3a and
=
the Supporting Information, Figure S1, the C O stretching
vibrations (1700 cmÀ1) greatly attenuated in the COFs,
indicating the consumption of the aldehydes. The emergence
of two new signals at 1635 and 965 cmÀ1 were attributed to the
stretching and bending vibrations of the trans-vinylene bond,
indicating the formation of vinylene-linked COFs. In the
13C NMR spectra, the characteristic chemical shifts at 170 and
155 ppm were assigned to the carbon atoms of the triazine
ring and pyridinyl ring. The signals at 23 and 44 ppm were
assigned to the ethyl carbons, also indicating the formation of
For ionic polymeric materials, the counter ions that
balance the charged states of polymeric backbones play
a crucial role in tuning physicochemical properties such as
porosity, morphology, and electronic structure. Ion exchange
is one of the most common methods of incorporating various
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Angew. Chem. Int. Ed. 2021, 60, 1 – 8
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