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mainly on the pyrene knots (Figure S5). In contrast to being
distributed throughout the framework of TAPFY-COF, the
LUMO wave function is localized on the interlayer conjugated
chains in TAPFY-COF-P (Figure S6). This indicates that more
significant charge separation in the excited state is likely to
occur after polymerization. The above results demonstrate that
the formation of conjugated enyne chains facilitates the charge
transfer between the layers as well as the charge separation in
the layers.
Next we synthesized TAPFY-COF under solvothermal
condition in an isolated yield of 90%. Thermogravimetric
analysis (TGA) reveals that TAPFY-COF showed no weight
loss up to 500 °C under N atmosphere (Figure 2a). Based on
2
the differential scanning calorimetry (DSC) and variable-
subsequent topology polymerization was conducted under 350
°
C for 6 h in the solid state to achieve complete reaction and
avoid solvent-induced changes of interlayer packing.
50−52
Further TGA performed under the same polymerization
happen during the SSTP procedure (Figure S8).
The successful syntheses of TAPFY-COF and TAPFY-COF-
P are proved by Fourier transform infrared (FT-IR) spectros-
1
3
copy, C cross-polarization/magic angle spinning solid-state
1
3
nuclear magnetic resonance ( C CP/MAS ssNMR) spectros-
copy, elemental analyses (EA), powder X-ray diffraction
(
PXRD), and N adsorption measurements. Comparing with
2
−
1
TAPFY-COF, a new peak appears around 1510 cm , assigned
to the characteristic vibration of CC in the enyne unit, and
the CN vibration is retained in the FT-IR spectra of TAPFY-
COF-P. Moreover, after SSTP, the CC stretch of the
−
1
aromatic ring groups around 1580 cm shifts to a higher
−
1
wavenumber, around 1605 cm (Figure 2b, Figure S9),
indicating the obvious change in the chemical environment of
the aromatic rings resulting from a high degree of trans-
formation of the diacetylene groups.
Figure 1. (a) Schematic representation of the two possible
polymerization routes of diacetylene. (b) Structures of TAPFY-COF
before and after SSTP. (c) Band structure of TAPFY-COF and
TAPFY-COF-P.
13
From the C CP/MAS ssNMR spectra (Figure 2c), the
completion of diacetylene polymerization is evidenced by the
disappearance of the two signals at around 75 and 80 ppm
assigned to the carbons with different chemical environments
in the diacetylene group (Figure 2b,c), revealing the fully
conversion of diacetylene. The ssNMR spectrum of TAPFY-
COF-P becomes less resolved, which reveals that the carbon
atoms have similar but not exactly chemical equivalent
environments caused by the imperfectness in the enyne chains.
The EA analyze results shows that the elemental contents (C,
theoretical calculated values (Table S1). Compared with the
UV−vis diffuse reflectance spectra of TAPFY-COF, the
absorption band of TAPFY-COF-P is significantly broadened
and a typical π−π* transitions absorption peak of poly-
offset (Figure 1b, Table S2). In addition, the phenyl ring
adjacent to the pyrene unit is obviously rotated with a dihedral
angle of 41.6° due to the steric hindrance of the neighboring
hydrogen atoms. The intermolecular distance between the
diacetylene groups is 3.85 Å. After polymerization, the layers
are linked by polymeric chains with alternating double−triple
bonds (Figure 1b); correspondingly, the force-field optimized
calculated by DFT. TAPFY-COF exhibits a relatively flat
highest occupied molecular orbital (HOMO) band and lowest
unoccupied molecular orbital (LUMO) band, indicating that
the effective mass in TAPFY-COF is larger and its in-plane and
out-of-plane charge transport is limited. This is due to the
broken conjugation in the distorted planar layers. In
comparison, TAPFY-COF-P displays obvious band dispersion
in the out-of-plane direction, revealing more effective charge
53−55
diacetylene appears around 570 nm (Figure 2g).
In
addition, the experimental deduced band gaps are 2.25 and
1.54 eV for TAPFY-COF and TAPFY-COF-P, respectively,
which are agree with the theoretical calculations.
PXRD and theoretical simulations were carried out to
deduce their crystal structure. TAPFY-COF shows prominent
peaks with 2θ at 2.74, 5.62, 8.46, and ∼23.96°, which can be
assigned to (110), (220), (420), and (001) facets, respectively
(Figure 2d). The Pawley refinement result, as well as the
cell, matches the experimental results (Figure S11). TAPFY-
48
transport through the enyne-linked layers. After SSTP, the
bandgap narrows from ∼2.0 to ∼1.5 eV due to the formation
of conjugated enyne chains, which is beneficial for the increase
49
of intrinsic carrier concentration (Figure 1c). In addition, the
HOMO wave functions of the two COFs are both localized
7
898
J. Am. Chem. Soc. 2021, 143, 7897−7902