Vinylene-Bridged Two-Dimensional Covalent Organic Frameworks via Knoevenagel Condensation of Tricyanomesitylene

Article abstract of DOI:10.1021/jacs.0c04594

Vinylene-bridged covalent organic frameworks (COFs) have shown great potential for advanced applications because of their high chemical stability and intriguing semiconducting properties. Exploring new functional monomers available for the reticulation of vinylene-bridged COFs and establishing effective reaction conditions are extremely desired for enlarging the realm of this kind of material. In this work, a series of vinylene-bridged two-dimensional (2D) COFs are synthesized by Knoevenagel condensation of tricyanomesitylene with ditopic or tritopic aromatic aldehydes. With use of appropriate secondary amines as catalysts, high-crystalline vinylene-bridged COFs were achieved, exhibiting long-range ordered structures, well-defined nanochannels, high surface areas (up to 1231 m2 g-1), and excellent photophysical properties. Under a low loading amount and short reaction time, they enable aerobic photocatalytic transformation of arylboronic acids to phenols with high efficiency and excellent recyclability. This work demonstrates a new functional monomer, tricyanomesitylene, feasible for the general synthesis of vinylene-bridged COFs with potential application in photocatalytic organic transformation, which instigates further research on such kind of material.

Full text of DOI:10.1021/jacs.0c04594

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Article
Vinylene-Bridged 2D Covalent Organic Frameworks
via Knoevenagel Condensation of Tricyanomesitylene
Shuai Bi, Palani Thiruvengadam, Shice Wei, Wenbei Zhang, Fan Zhang,
Lusha Gao, Junsong Xu, Dongqing Wu, Jie-Sheng Chen, and Fan Zhang
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.0c04594 • Publication Date (Web): 12 Jun 2020
Downloaded from pubs.acs.org on June 13, 2020
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Vinylene-Bridged 2D Covalent Organic Frameworks via Knoevenagel
Condensation of Tricyanomesitylene
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§
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Shuai Bi , Palani Thiruvengadam , Shice Wei, Wenbei Zhang, Fan Zhang, Lusha Gao, Junsong Xu,
Dongqing Wu, Jie-Sheng Chen and Fan Zhang*
School of Chemistry and Chemical Engineering, State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University,
Shanghai 200240, China
Supporting Information Placeholder
ABSTRACT: Vinylene-bridged covalent organic frameworks (COFs) have shown great potential for advanced applications due to
their high chemical stability and intriguing semiconducting properties. Exploring new functional monomers available for the
reticulation of vinylene-bridged COFs and establishing effective reaction conditions are extremely desired for enlarging the realm of
this kind of material. In this work, a series of vinylene-bridged 2D COFs are synthesized by Knoevenagel condensation of
tricyanomesitylene with ditopic or tritopic aromatic aldehydes. By using appropriate secondary amines as catalysts, high crystalline
vinylene-bridged COFs were achieved, exhibiting long-range ordered structures, well-defined nanochannels, high surface areas (up
2
-1
to 1231m g ) and excellent photophysical properties. Under low loading amount and short reaction time, they enable aerobic
photocatalytic transformation of arylboronic acids to phenols with high efficiency and excellent recyclability. This work demonstrates
a new functional monomer tricyanomesitylene feasible for the general synthesis of vinylene-bridged COFs with potential application
on photocatalytic organic transformation, which instigates further research on such kind of material.
Knoevenagel condensation with aldehyde at its phenyl methyl
INTRODUCTION
groups. The resultant -extended fluorophores exhibit
Reticulating organic building blocks into promising covalent
organic framework (COF) via carbon-carbon double bond
interesting nonlinear optical properties.19 In 2017, we have
reported the synthesis of a series of vinylene-bridged
conjugated porous polymers by using TCM as the key building
block to condense with multiple aldehyde-substituted
polyphenylenes. In addition, we preliminarily studied their
semiconducting properties and photocatalytic water-splitting
(C═C) is becoming one of the most attractive topics for organic
porous materials, because a COF linked with such bond features
high chemical stability and efficient π-electron delocalization,
outperforming other COFs linked by boroxine, borate or imine
1
-3
20
bonds. Over the past four years, several cyanovinylene [–
CH═C(CN)–] or vinylene (–CH═CH–) bridged COFs have
been synthesized by Knoevenagel (or Aldol) condensation,
showing tremendous potential applications in photocatalysis,
activities. However, our attempt to improve the crystallinity
of such kind of porous polymers is unsuccessful at that time.
Hereby, we focus on optimizing the condensation conditions
by activating the monomers at not only the aryl methyl groups,
but also the carbonyl groups. After extensive screening of
reaction conditions, we successfully obtained three 2D
vinylene-bridged COFs by condensation of TCM with ditopic
or tritopic aromatic aldehydes using secondary amines as base
catalysts in a binary solvent at a relatively high reaction
temperature (180 ℃). Their long-range ordered honeycomb-
like structures with regular nanopore channels and high surface
4
-11
magnetism and electrochemical energy storage.
However,
such COFs are still in the infant stage, far less than those
classical ones, likely attributed to the lack of available building
blocks for the formation of C═C bond via thermodynamically
reversible process.
In comparison with cyanovinylene linkage, vinylene linkage
seems to be more favorable to create high-crystalline C═C
linked COFs, probably associated with its higher geometric
symmetry and less steric interference.
kinds of monomers, 3,5-dicyano-2,4,6-trimethylpyridine and
2
-1
areas (up to 1231 m g ) were characterized by powder X-ray
diffraction (PXRD), high resolution transmission electron
microscopy (HRTEM) and nitrogen sorption analyses,
1
2, 14, 16
Very recently, two
trimethyltriazine were found available for the effective
synthesis of vinylene-bridged COFs.
2
respectively. Their fully sp -carbon connected backbones with
13-18
The electron-
donor-acceptor characters endow them with substantial
withdrawing groups (e.g., pyridinyl nitrogen, cyano substituent)
in those monomers are able to trigger the condensation reaction
between their acidic methyl groups and aldehydes. Beyond
those two monomers, it’s worth noting that an electron-
deficient molecule tricyanomesitylene (TCM) was used to
synthesize vinylene-linked dendritic small molecules through
21,22
semiconducting properties.
Upon visible-light irradiation,
these COFs efficiently catalyzed oxidative hydroxylation of
arylboronic acids to phenols with low loading amount and short
reaction time, comparable to those homogeneous catalysts, but
23,24
recyclable.
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Scheme 1. Synthetic Routes to COF-p-3Ph, COF-p-2Ph and COF-m-3Ph.
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25-27
28,29
mechanism)
mechanism)
or a carboanion intermediate (Hann-Lapworth
via the activation of the carbonyl compound or
RESULTS AND DISCUSSION
As depicted in Scheme 1, a secondary amine-catalyzed
Knoevenagel condensation was applied to link TCM with
aromatic multi-aldehydes [i.e., 4,4”-diformyl-p-terphenyl
the methylene (or methyl) compound, respectively. Given the
piperidine is effective in synthesizing COF-p-3Ph, we
hypothesized that the reaction likely undergoes Knoevenagel
mechanism via iminium cation intermediate, and varying the
secondary amine catalysts might be able to improve the
crystallinity of COF-p-2Ph and COF-m-3Ph. Therefore, a series
of secondary amine including dimethylamine, diethylamine,
diisopropylamine, dibenzylamine, pyrrolidine and morpholine
were screened. Under an optimized condition by using
dimethylamine as base catalyst and a binary solvent of DMF/o-
DCB (1/1, v/v), COF-p-2Ph and COF-m-3Ph with high
crystallinity were achieved (Tables S2 and S3, Figures S19 and
S20).
(
DFPTP), 4,4'-diformyl-1,1'-biphenyl (DFBP) or 1,3,5-tris(4-
formylphenyl)benzene (TFPB)] to form three vinylene-bridged
COFs which were denoted as COF-p-3Ph, COF-p-2Ph and
COF-m-3Ph, respectively. Highly crystalline samples were
achieved after extensive screening of reaction conditions,
including reaction temperature, solvents and catalysts. Firstly,
we took COF-p-3Ph as an example (Table S1, Figure S18).
According to our previous results, TCM was effectively reacted
with DFPTP to form cross-linked polymer by using N,N-
dimethylformamide (DMF) as solvent and piperidine as catalyst
2
0
at 150 °C. However, the resulting product was characterized
to be amorphous. After elevating the reaction temperature to
1
Scheme 2. Proposed Mechanism for Secondary Amine-
Catalyzed Knoevenagel Condensation of Tricyanomesitylene
and Aromatic Aldehyde.
80 °C, COF-p-3Ph with low crystallinity was achieved,
implying that the reaction temperature plays a significant role
in the crystallization process by improving the reversibility of
the C=C bond forming reaction. Further screening the solvents
system gave highly crystalline COF-p-3Ph in a binary solvent
of DMF and ortho-dichlorobenzene (o-DCB) (DMF/o-DCB:
1/1, v/v). Subsequently, we applied this optimum condition to
synthesize COF-p-2Ph and COF-m-3Ph, but the resulting COFs
only show weak crystallinity (Figures S19 and S20), probably
due to the insufficient reversibility for structure correction
during the crystallization process.
In general, a based-catalyzed Knoevenagel condensation can
occur through an iminium intermediate (Knoevenagel
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Figure 1. PXRD patterns of (a) COF-p-3Ph, (b) COF-p-2Ph and (c) COF-m-3Ph. Comparison between the experimental profiles (red line),
Pawley refined profiles (black line), the simulated patterns for eclipsed (AA) stacking mode (cyan line), the Bragg positions (green bar) and
the refinement differences (violet line). Inset: Corresponding refined 2D crystal structural models of COF-p-3Ph, COF-p-2Ph and COF-m-
3
Ph assuming the eclipsed (AA) stacking mode.
Accordingly, a plausible mechanism of the secondary amine-
hexagonal unit cells for the three COFs (COF-p-3Ph: P6/m, a =
b = 38.744 Å and c = 3.469 Å, R = 2. 60%, RWP = 3.37%);
COF-p-2Ph: P6, a = b = 30.288 Å and c = 3.624 Å, R = 2.65%,
WP = 3.54%; COF-m-3Ph: P3, a = b = 18.790 Å and c = 3.699
Å, R = 3.48%, RWP = 4.55%).
activated Knoevenagel condensation were proposed as depicted
in Scheme 2: the reaction might be promoted through an
iminium cation intermediate (A), which could be accessed by
condensation of an aldehyde with a secondary amine (C). And
then, an addition reaction could smoothly occur on account of
the appropriate electrophilicity of iminium cation intermediate
and the small-size dimethylamine moiety, leading to the
formation of an adduct B, which undergoes the elimination
process to form vinylene-linked structures. The experiments for
the syntheses of these three COFs were conducted under the
protection of inert atmosphere (such as argon), and kept in a
strictly sealed state for avoiding any exposure to the air. After
P
P
R
P
In their nitrogen sorption isotherms (Figure 2a), COF-p-3Ph
and COF-p-2Ph feature type-IV reversible isotherm, indicative
of their mesoporous character. While COF-m-3Ph shows type-
I reversible isotherm, suggesting its microporous structure. The
calculated Brunauer-Emmett-Teller (BET) surface areas of
COF-p-3Ph, COF-p-2Ph and COF-m-3Ph are 963, 1036 and
2
-1
1231 m g , respectively much higher than those of 564, 750
2
-1
and 834 m g of their amorphous samples. These results
suggest that the high order within the lattices of the COFs
positively contributes to their increased surface area in
comparison with amorphous porous polymers. The pore size
distributions (PSDs) were evaluated with cylindrical quenched-
solid density functional theory (QSDFT) equilibrium model.
The PSDs of COF-p-3Ph, COF-p-2Ph and COF-m-3Ph exhibit
the maxima at 3.0 nm, 2.2 nm and 1.7 nm, respectively, well in
line with the predicted pore diameter for eclipsed (AA) stacking
geometries of the frameworks based on solvent accessible
surfaces (Figures S30~S32).
7
2 hours, the COFs were collected as yellow powder by
conventional purification workup (see the experimental section
in Supporting Information). In order for comparison, three
porous polymers, also known as the amorphous samples of the
COFs (denoted as OB-POP-3, OB-POP-2 and OB-POP-4) were
synthesized by using only DMF as solvent and piperidine as
20
catalyst at 150 °C under vigorous stirring.
In the experimental PXRD patterns of the COFs (Figure 1),
the intense (100) diffraction peaks of COF-p-3Ph, COF-p-2Ph
and COF-m-3Ph were observed at 2θ = 2.54°, 3.37° and 5.43°,
respectively. In addition, peaks at 2θ = 4.48° and 5.12° for
COF-p-3Ph and peaks at 2θ = 5.88° and 6.78° for COF-p-2Ph
correspond to their (110) and (200) planes, respectively. For
COF-m-3Ph, peaks at 2θ = 9.52°, 11.08°, 14.62° and
The chemical structures of these COFs were characterized by
13
Fourier transform infrared (FT-IR) and
C
cross-
polarization/magic angle spinning solid-state nuclear magnetic
resonance (CP/MAS ssNMR) spectroscopy (Figure 2b and 2c).
2
4.83°correspond to the (110), (200), (210), and (001) planes,
-1
In FT-IR spectra, the newly formed peaks at 1625 cm and 970
respectively. The sharp (100) reflections as well as the other
multiple reflections essentially revealed the high crystallinity of
the as-prepared COFs. Several models with different stacking
modes were generated in hexagonal 2D nets with hcb topology.
Comparison between experimental profiles and simulated
patterns suggests the three COFs are more likely to adopt the
eclipsed (AA) layer-stacking mode (Figures S24~S29). Pawley
refinements of the eclipsed (AA) stacking models towards the
experimental PXRD patterns were applied to produce
-1
cm are attributed to trans-C═C linkages. In these COF
samples, there are no detectable C═O stretching vibrations, and
-1
the intense peaks of cyano group at 2225 cm manifest the high
degree of polymerization. In CP/MAS ssNMR spectra, the
signals at ~115 ppm are assigned to cyano groups. The peaks at
~120 and ~140 ppm correspond to the olefinic carbons. The
strong resonances at 127 ppm originate from the aromatic
carbons. All these results essentially verify the structural
integrity of these vinylene-bridged COFs.
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Figure 2. (a) Nitrogen sorption isotherms. Inset: pore size distributions. (b) 13C CP/MAS NMR spectra. Asterisks denote spinning sidebands.
(c) FT-IR spectra.
Figure 3. (a) TEM image of COF-p-3Ph. (b) Enlarged view of a selected area in panel (a), the structural model is overlapped on the top. (c)
TEM image of COF-p-3Ph from different area, showing 1D channels with distance of 3 nm.
Scanning electron microscopy (SEM) images revealed the
particulate morphology of these vinylene-bridged COFs (Figures
S12~S14). HRTEM images further revealed the ordered internal
structures of the COFs. For example, the honeycomb-like porous
structure can be observed for COF-p-3Ph (Figure 3a and 3b), which
is in accordance with the structural model. The spacing of the lattice
fringe in Figure 3c is 3 nm, corresponding to the diameter of 1D
pore channel in COF-p-3Ph. The ordered lattice fringe of the other
two COFs (COF-p-2Ph and COF-m-3Ph) also can be well
distinguished on their HRTEM images (Figures S15 and S16),
manifesting their high crystallinity.
the backbones. Such phenomenon indicates the efficient π-electron
communication from the (poly-)phenylene donors to the cyano-
substituted phenyl acceptors via vinylene linkages. It is worth
noting that in comparison with their amorphous samples, the as-
prepared COFs show red-shifts on both absorption edges and
emission maxima, indicating the strengthened π-conjugated effect
in the crystalline structures (Figure 4a and Figure S6). Accordingly,
the optical band gaps of the COFs were determined from Kubelka-
Munk function as 2.27 eV, 2.33 eV and 2.48 eV for COF-p-3Ph,
COF-p-2Ph and COF-m-3Ph, respectively (Figure 4b). The energy
of valence band maximum (EVB) of the three COFs relative to
vacuum level were evaluated by UPS analyses (Figure 4d~4f). The
EVB was calculated by subtracting the UPS width from excitation
energy (He I, 21.2 eV). The EVB values of COF-p-3Ph, COF-p-2Ph
and COF-m-3Ph were thus calculated to be −6.1, −6.4 and −6.2 eV,
respectively. Considering their optical band gaps, the energy of
conduction band minimum (ECB) of COF-p-3Ph, COF-p-2Ph and
COF-m-3Ph were calculated as −3.8, −4.1 and −3.7 eV,
respectively. Therefore, the ECB of all three COFs are positioned
The electronic structures of these COFs are systematically
investigated by ultraviolet/visible diffuse reflectance spectroscopy
(UV/vis DRS) and ultraviolet photoelectron spectroscopy (UPS).
As shown in Figure 4a, COF-p-3Ph exhibits the most broad
absorption band among the three COFs, covering 240~600 nm with
the absorption edge at ca. 500 nm. COF-p-2Ph shows a slightly
blue-shifted absorption edge at ca. 475 nm. While, the absorption
edge at ca. 400 nm in the much higher energy region was found for
COF-m-3Ph. Notably, the shoulder bands at ca. 570 nm, 550 nm
and 520 nm were observed for COF-p-3Ph, COF-p-2Ph and COF-
m-3Ph, respectively, typically attributable to the intramolecular
charge transfer (ICT) arising from the donor-acceptor characters of
•−
higher than the potential of O /O
2
2
(−4.16 eV) (Figure 4c),
allowing for reducing molecular oxygen to superoxide radical
anion if they were excited by light with appropriate photon
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light-driven oxidative organic transformation. With regard to the
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intriguing optoelectronic properties of the as-prepared COFs, their
photocatalytic performance of aerobic transformation of
arylboronic acids to phenols, in particular combined with their
reusability and recycling, were examined. In a typical performance,
a COF sample was employed as photosensitizer, with triethylamine
as sacrificial agent, oxygen as clean oxidant, CH
3
CN as solvent and
2
-naphthylboronic acid as substrate. After visible light irradiation
for 4 hours, the yield of 2-naphthol was evaluated. The data
collected in Table 1 show the necessary presence of visible light
(entry 2), oxygen source (entry 3) and COF photocatalyst (entry 4)
to proceed the reaction. A 99% conversion was achieved by COF-
p-3Ph, which was much higher than those of COF-p-2Ph and COF-
m-3Ph (entry 5~6). Also, COF-p-3Ph distinctly outperformed its
amorphous sample (OB-POP-3) which only showed 40%
conversion under the identical experimental conditions (entry 7).
The amorphous samples of COF-p-2Ph and COF-m-3Ph (OB-POP-
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and OB-POP-4) were also less efficient than the crystalline COFs
(entries 8 and 9). The higher efficiency of COF-p-3Ph was mainly
attributed to its strong light-harvesting capability originating from
its intrinsic extended π-conjugated backbone, as compared to COF-
p-2Ph and COF-m-3Ph. Notably, even using less amount of COF-
p-3Ph (1 or 3 mg) also led to high conversion efficiency (Table S7).
Additionally, with air as oxidant source, COF-p-3Ph also delivered
7
1
5% yield of 2-naphthol after 4 hours and 99% after 8 hours (entry
0), which is highly reliable and sustainable for practical
3 4
application. For comparison, graphitic carbon nitride (g-C N ) was
also tested under identical conditions, showing only 28%
conversion (entry 11).
Figure 4. (a) UV/vis absorption spectra of the three COFs and the
corresponding amorphous OB-POPs. (b) The bandgaps determined
from Kubelka-Munk function. (c) Energy of band positions of the
COFs. (d, e and f) UPS spectra of the COFs.
Table 2. Scope of Substrates by Using COF-p-3Ph as
a
Photocatalyst
Table 1. Screening of Reaction Conditions for
Photocatalytic Oxidative Hydroxylation of Arylboronic
visible light ( > 420 nm)
COF-p-3Ph, TEA
a
Ar-B(OH)2
Ar-OH
Acids to Phenols
CH3CN, O2 1 atm., r.t., 4 hrs
visible light ( > 420 nm)
B(OH)2
OH
entry
1
substrate
product t (h)
yield(%)b
COF photocatalyst, TEA
CH3CN, O2 1 atm., r.t., 4 hrs
4
4
4
4
99
99
99
96
yield(%)b
2
3
4
entry
1
photocatalyst
COF-p-3Ph
COF-p-3Ph
COF-p-3Ph
none
visible light
O
2
+
−
+
+
+
+
+
+
+
+
+
+
99
trace
trace
trace
74
2
+
−
+
+
+
+
+
+
+
+
3
4
5
COF-p-2Ph
COF-m-3Ph
OB-POP-3c
OB-POP-2d
OB-POP-4e
COF-p-3Phf
5
6
4/8
4/8
60/70
56/77
6
60
7
40
8
37
9
34
10
99
7
8
4
4
99
85
11
g-C
3
N
4
28
aReaction conditions: 2-Naphthylboronic acid (1.0 mmol), COF
catalyst (5 mg), CH CN (5 mL), TEA (3.0 mmol, 3.0 equiv.),
irradiation by 300 W Xenon light with λ > 420 nm cut-off filter, 4
3
aReaction conditions: Arylboronic acid (1.0 mmol), COF-p-3Ph (5
b
c
hours. Isolated yield. Amorphous sample of COF-p-3Ph.
d
e
mg), CH CN (5 mL), TEA (3.0 mmol, 3.0 equiv.), irradiation by
Amorphous sample of COF-p-2Ph. Amorphous sample of COF-
3
b
f
300 W Xenon light with λ > 420 nm cut-off filter. Isolated yield.
m-3Ph. Air is oxygen source and reaction time is 8 hours.
The scope of substrates was further investigated (Table 2). The
substrates with electron-withdrawing substituents gave nearly
Generating superoxide radical anion from molecular oxygen is
one of the most green and sustainable strategies for the visible-
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quantitative yield (entry 1~3). By contrast, it took relatively long
superoxide radical anion by the photo-induced electrons on the
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5
5
6
reaction time to convert electron-rich substrates to the
corresponding phenols in good yields (entry 4~6). The relatively
low yields in entry 5 and 6 could be reasonably attributed to the
electron-rich substituent effect and steric effect of the substrates,
which is consistent with the previously reported homogeneous
excited COF-p-3Ph. Subsequently, the O-labeling experiments
revealed that the hydroxy oxygen atom of the product originated
from molecular oxygen rather than from water (Figures S34 and
S35). Thus a plausible catalytic cycle was proposed that the
superoxide radical anion attacks the boron atom of the boronic acid
and undergoes a sequence of radical quenching, rearrangement and
23
system. While, for the recently reported COF-based photocatalyst
LZU-190, the larger loading amount (21.2 mg, 0.015 mmol) and
much longer reaction time (48~96 hours) were required.
Importantly, COF-p-3Ph can be easily isolated by filtration and
reused for the next photocatalytic cycle, showing no noticeable
decay either in photocatalytic activity or crystalline structure after
hydrolysis, eventually leading to the formation of phenols (Figure
3
1
23,31
S36).
In addition, we obtained a conversion vs. time plot for the
oxidation of 2-naphthylboronic acid by COF-p-3Ph under the
standard conditions (Figure 5a). We found that the substrate was
consumed followed by the gradual generation of product without
the observation of other stable intermediates. According to the
reaction profile, the turn over frequency (TOF) of 2-
naphthylboronic acid to 2-naphthol catalysed by COF-p-3Ph was
0
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1
0 runs (Figure 5b~5f). Furthermore, the mechanism of this
reaction was investigated by spin-trapping, isotope labeling and
kinetic experiments. Firstly, COF-p-3Ph was added into the O
2
-
-2 -1
saturated methanol solution of 5,5-dimethyl-1-pyrroline N-oxide
(DMPO). After irradiating the solution by visible light for 60
seconds, the electron spin resonance (ESR) spectra show the typical
signal of the adduct of DMPO and superoxide radical anion (Figure
calculated to be 1.5  10 s , which is significantly higher than that
of the previously reported COF LZU-190 (3  10-5 -1) (note the
s
mole number of COF was calculated based on the molecular weight
of its unit cell).31
3
2
S33), manifesting that the molecular oxygen was reduced to
Figure 5. (a) Conversion vs. time plot for the photocatalytic transformation of 2-naphthylboronic acid to 2-naphthol by using COF-p-3Ph as
the photocatalyst. (b) Recycling of COF-p-3Ph for the photo-oxidative hydroxylation of 2-naphthylboronic acid to 2-naphthol. (c~f) Nitrogen
13
sorption isotherms, PXRD patterns, C CP/MAS NMR spectra and FT-IR spectra of the as-synthesized COF-p-3Ph and the sample after 10
runs of photocatalysis.
This work not only enlarged the realm of C═C linked COFs, but
also contributed to the exploration of 2D conjugated polymers or
graphene analogues with well-defined structures and exceptional
semiconducting properites.
CONCLUSIONS
In conclusion, a series of vinylene-bridged COFs were
successfully synthesized by Knoevenagel condensation of
tricyanomesitylene with ditopic or tritopic aromatic aldehydes.
2
These crystalline fully sp -carbon-connected frameworks exhibit
EXPERIMENTAL SECTION
All experimental procedures are provided in the Supporting
Information.
high surface areas and excellent semiconducting propeties,
including superior -delocalization, intensive light-harvesting
capability and tunable band structures. Consequently, these COFs
enable visible-light-driven aerobic oxidation of aryl boronic acids
to aryl phenols in a wide scope of substrates with high efficiency.
ASSOCIATED CONTENT
Supporting Information.
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Journal of the American Chemical Society
The Supporting Information is available free of charge on the ACS
(12) Lee, S.; Chen, C.-H.; Flood, A. H. A pentagonal cyanostar
macrocycle with cyanostilbene CH donors binds anions and forms
dialkylphosphate [3]rotaxanes. Nat. Chem. 2013, 5, 704-710.
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Publications website at http://pubs.acs.org. Detailed synthetic
procedures, characterization of materials and photocatalytic
experiments.
(13) Bi, S.; Yang, C.; Zhang, W.; Xu, J.; Liu, L.; Wu, D.; Wang, X.;
Han, Y.; Liang, Q.; Zhang, F. Two-dimensional semiconducting
covalent organic frameworks via condensation at arylmethyl carbon
atoms. Nat. Commun. 2019, 10 (1), 2467.
Corresponding Author
*
fan-zhang@sjtu.edu.cn
(14) Lyu, H.; Diercks, C. S.; Zhu, C.; Yaghi, O. M. Porous
Author Contributions
§S. B. and P. T. contributed equally.
Crystalline Olefin-Linked Covalent Organic Frameworks. J. Am.
Chem. Soc. 2019, 141 (17), 6848-6852.
(
15) Xu, J.; He, Y.; Bi, S.; Wang, M.; Yang, P.; Wu, D.; Wang, J.;
Zhang, F. An Olefin-Linked Covalent Organic Framework as a
Flexible Thin-Film Electrode for High-Performance Micro-
Supercapacitor. Angew. Chem. Int. Ed. 2019, 58, 12065.
16) Jadhav, T.; Fang, Y.; Patterson, W.; Liu, C.-H.; Hamzehpoor,
Notes
a
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The authors declare no competing financial interest.
(
ACKNOWLEDGMENT
We thank the National Natural Science Foundation of China
E.; Perepichka, D. F. 2D Poly(arylene vinylene) Covalent Organic
Frameworks via Aldol Condensation of Trimethyltriazine. Angew.
Chem. Int. Ed. 2019, 58 (39), 13753-13757.
(21574080, 21774072, 21720102002). Furthermore, this work was
(17) Acharjya, A.; Pachfule, P.; Roeser, J.; Schmitt, F.-J.; Thomas,
financially supported by the Shanghai Committee of Science and
Technology for financial support within the projects (16JC1400703)
and Open Project Program of the State Key Laboratory of Inorganic
Synthesis and Preparative Chemistry (2019-01, Jilin University).
We thank Xinqiu Guo, Qunli Rao, Yan Li and Jie Zhang in the
Instrumental Analysis Center of SJTU for their help on the TEM,
PXRD, TGA and nitrogen physisorption measurements.
A. Vinylene-Linked Covalent Organic Frameworks by Base-Catalyzed
Aldol Condensation. Angew. Chem. Int. Ed. 2019, 58 (42), 14865-
1
4870.
(18) Wei, S.; Zhang, F.; Zhang, W.; Qiang, P.; Yu, K.; Fu, X.; Wu,
D.; Bi, S.; Zhang, F. Semiconducting 2D Triazine-Cored Covalent
Organic Frameworks with Unsubstituted Olefin Linkages. J. Am.
Chem. Soc. 2019, 141 (36), 14272-14279.
(19) Cho, B. R.; Park, S. B.; Lee, S. J.; Son, K. H.; Lee, S. H.; Lee,
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31) Wei, P.-F.; Qi, M.-Z.; Wang, Z.-P.; Ding, S.-Y.; Yu, W.; Liu,
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Q.; Wang, L.-K.; Wang, H.-Z.; An, W.-K.; Wang, W. Benzoxazole-
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Solutions. Can. J. Chem. 1974, 52 (20), 3549-3553.
Table of Content
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Scheme 1. Synthetic Routes to COF-p-3Ph, COF-p-2Ph and COF-m-3Ph.
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Scheme 2. Proposed Mechanism for Secondary Amine-Catalyzed Knoevenagel Condensation of
Tricyanomesitylene and Aromatic Aldehyde.
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Figure 1. PXRD patterns of (a) COF-p-3Ph, (b) COF-p-2Ph and (c) COF-m-3Ph. Comparison between the
experimental profiles (red line), Pawley refined profiles (black line), the simulated patterns for eclipsed (AA)
stacking mode (cyan line), the Bragg positions (green bar) and the refinement differences (violet line).
Inset: Corresponding refined 2D crystal structural models of COF-p-3Ph, COF-p-2Ph and COF-m-3Ph
assuming the eclipsed (AA) stacking mode.
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Figure 2. (a) Nitrogen sorption isotherms. Inset: pore size distributions. (b) 13C CP/MAS NMR spectra.
Asterisks denote spinning sidebands. (c) FT-IR spectra.
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Figure 3. (a) TEM image of COF-p-3Ph. (b) Enlarged view of a selected area in panel (a), the structural
model is overlapped on the top. (c) TEM image of COF-p-3Ph from different area, showing 1D channels with
distance of 3 nm.
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Figure 4. (a) UV/vis absorption spectra of the three COFs and the corresponding amorphous OB-POPs. (b)
The bandgaps determined from Kubelka-Munk function. (c) Energy of band positions of the COFs. (d, e and
f) UPS spectra of the COFs.
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Figure 5. (a) Conversion vs. time plot for the photocatalytic transformation of 2-naphthylboronic acid to 2-
naphthol by using COF-p-3Ph as the photocatalyst. (b) Recycling of COF-p-3Ph for the photo-oxidative
hydroxylation of 2-naphthylboronic acid to 2-naphthol. (c~f) Nitrogen sorption isotherms, PXRD patterns,
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3C CP/MAS NMR spectra and FT-IR spectra of the as-synthesized COF-p-3Ph and the sample after 10 runs
of photocatalysis.
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Table of Contents (TOC) graphic
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