De Novo Design and Facile Synthesis of 2D Covalent Organic Frameworks: A Two-in-One Strategy

Article abstract of DOI:10.1021/jacs.9b03463

We herein develop a two-in-one molecular design strategy for facile synthesis of 2D imine based covalent organic frameworks (COFs). The integration of two different functional groups (i.e., formyl and amino groups) in one simple pyrene molecule affords a bifunctional building block: 1,6-bis(4-formylphenyl)-3,8-bis(4-aminophenyl)pyrene (BFBAPy). Highly crystalline and porous Py-COFs can be easily prepared by the self-condensation of BFBAPy in various solvents, such as CH₂Cl₂, CHCl₃, tetrahydrofuran, methanol, ethanol, acetonitrile, and dimethylacetamide, etc. The current work, to the best of our knowledge, is a rare case of COF synthesis that exhibits excellent solvent adaptability. Highly crystalline Py-COF thin films have been facilely fabricated on various substrates and exhibit potential applications in hole transporting layers for perovskite solar cells. Furthermore, the versatility of this two-in-one strategy was also verified by two additional examples. The current work dramatically reduces the difficulty of COF synthesis, and such two-in-one strategy is anticipated to be applicable for the synthesis of other COFs constructed by different building blocks and linkages.

Full text of DOI:10.1021/jacs.9b03463

Subscriber access provided by Nottingham Trent University
Article
De Novo Design and Facile Synthesis of 2D Covalent
Organic Frameworks: A Two-in-One Strategy
Yusen Li, Qing Chen, Tiantian Xu, Zhen Xie, Jingjuan Liu,
Xiang Yu, Shengqian Ma, Tianshi Qin, and Long Chen
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.9b03463 • Publication Date (Web): 13 Aug 2019
Downloaded from pubs.acs.org on August 13, 2019
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a service to the research community to expedite the dissemination
of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in
full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully
peer reviewed, but should not be considered the official version of record. They are citable by the
Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore,
the “Just Accepted” Web site may not include all articles that will be published in the journal. After
a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web
site and published as an ASAP article. Note that technical editing may introduce minor changes
to the manuscript text and/or graphics which could affect content, and all legal disclaimers and
ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or
consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W.,
Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 7
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
De Novo Design and Facile Synthesis of 2D Covalent Organic
Frameworks: A Two-in-One Strategy
Yusen Li,† Qing Chen,§ Tiantian Xu,† Zhen Xie,† Jingjuan Liu,† Xiang Yu,‡ Shengqian Ma,⊥ Tianshi
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Qin,§ Long Chen*,†
†Department of Chemistry and Tianjin Key Laboratory of Molecular Optoelectronic Science, Tianjin University, Tianjin
300072, China
‡Analytical and Testing Center, Jinan University, Guangzhou 510632, China
§Institute of Advanced Materials (IAM), Nanjing Tech University (Nanjing Tech), Nanjing 210009, China
⊥Department of Chemistry, University of South Florida, 4202 East Fowler Avenue, Tampa, Florida 33620, United States
Supporting Information Placeholder
ABSTRACT: We herein develop a two-in-one molecular design strategy for facile synthesis of 2D imine based covalent organic frame-
works (COFs). The integration of two different functional groups (i.e. formyl and amino groups) in one simple pyrene molecule affords a
bifunctional building block: 1,6-bis(4-formylphenyl)-3,8-bis(4-aminophenyl)pyrene (BFBAPy). Highly crystalline and porous Py-COFs can
be easily prepared by the self-condensation of BFBAPy in various solvents, such as CH2Cl2, CHCl3, tetrahydrofuran, methanol, ethanol,
acetonitrile, and dimethylacetamide, etc. The current work, to the best of our knowledge, is a rare case of COF synthesis that exhibits
excellent solvent adaptability. Highly crystalline Py-COF thin films have been facilely fabricated on various substrates and exhibit potential
applications in hole transporting layers for perovskite solar cells. Furthermore, the versatility of this two-in-one strategy was also verified by
two additional examples. The current work dramatically reduces the difficulty of COF synthesis, and such two-in-one strategy is anticipated
to be applicable for the synthesis of other COFs constructed by different building blocks and linkages.
INTRODUCTION
Scheme 1. Schematic diagrams for 2D COFs constructed by (a)
conventional self- and co-condensation methods and (b) our
new two-in one strategy
Covalent organic frameworks (COFs) are an emerging class of
crystalline porous materials which feature fascinating regular
structures and versatile functions.1 Since the seminal work re-
ported by Yaghi in 2005,1a COFs have received increasing re-
search interest because of their promising applications in gas
sorption and separation,2 catalysis,3 environmental remedia-
tion,4 sensing,5 drug delivery,6 energy storage7 and conversion8
etc. Many synthetic efforts have been devoted to advance the
development of COFs and great successes have been achieved
such as metal triflate assisted COF synthesis,9a p-toluene sul-
fonic acid monohydrate (PTSA•H2O) assisted solid state syn-
thesis,9b and mechanochemical synthesis9c etc. However, most
of the reported COFs are synthesized either by two-component
or multiple-component10 co-condensation of at least two mono-
mers bearing respectively different functional groups, with the
exception of self-condensation of boronic acid (e.g. COF-11a)
or aromatic nitriles (i.e. CTFs11) (Scheme 1a). Furthermore,
COFs are mostly prepared in delicately screened solvent mix-
tures and suffer from exhaustive trial-and-error procedures on
selection and adjustment of the synthetic condition parameters
like solvent combinations, temperature, reaction time, concen-
trations, pressure etc.12a Thus, a de novo molecular design strat-
egy to simplify the synthesis of COFs in a more reliable and
versatile way is highly desirable for advancing this research
area.
solubility difference. In most cases, the monomers are only par-
tially dissolved during the solvothermal synthesis.12a It is hardly
to find a suitable solvent combination in which the monomers
are soluble and maintain the stoichiometry to ensure the suffi-
cient 2D or 3D polymerization. To solve this dilemma, we en-
vision that merging two different functional groups of the co-
monomers into a single molecule (i.e. “two-in-one” strategy)
could bring several advantages: (i) the ideal stoichiometry could
be perfectly maintained either in homogeneous or heterogene-
ous states during the polymerization process; (ii) the solvent
We reason that one possible cause for the difficulties in pre-
paring highly crystalline COFs lies in the deviation of the
proper ratios among the dissolved co-monomers due to the
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 2 of 7
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 1. (a) The synthesis of Py-COF using single bifunctional monomer BFBAPy; (b) Experimental PXRD patterns of Py-COFDCM (black),
Pawley refinement (red), their difference (green), simulated profiles using AA-stacking (purple) and AB-stacking (dark yellow) modes; (c)
Unit cells of AA-stacking and (d) AB-stacking mode.
adaptability could be greatly improved which could benefit the
pre-modification of the substrate for COF films growth or post-
fabrication of the COF films for device applications;13 last but
not least (iii) the reproducibility of COF synthesis and their
crystallinity could be greatly improved as well as the screening
process of synthetic conditions could be simplified and become
much easier.
it clearly indicates that Py-COF exhibits higher crystallinity
than Py-Py COF (Figure S34). Furthermore, the Py-Py COF
constructed by co-condensation method exhibits poor solvent
adaptability with largely solvent dependent crystallinity. (Fig-
ure S34b). Moreover, this two-in-one design strategy also facil-
itates successful growth of high quality Py-COF thin films on
various substrates like transparent glass, conducting indium tin
oxide (ITO) and silicon wafer with good crystallinity. In addi-
tion, two new COFs (BFBAEB-COF and BFBAEPy-COF, Fig-
ure 6) with dual-pore structures, which cannot be constructed
by a dual monomer approach (Schemes S9 and S10), had been
successfully synthesized to verify the versatility of this two-in-
one strategy.
For a proof-of-concept, herein we designed and synthesized
a new bifunctional monomer 1,6-bis(4-formylphenyl)-3,8-
bis(4-aminophenyl)pyrene (Figure 1a, BFBAPy) with two
formyl and two amino groups in a single pyrene core molecule
to construct 2D pyrene-based imine COF (Py-COF) through in-
termolecular self-condensation. Unlike most reported COFs
which involve the co-condensation of two or more kinds of
monomers with separately different functional groups, this bi-
functional module can be facilely used for the construction of
crystalline Py-COF in various solvents (Table S1). The stoichi-
ometry of the two different functional groups was strictly guar-
anteed (1:1) in these systems, which is beneficial to the for-
mation of regular structures. Actually, highly crystalline Py-
COFs were obtained not only in mixed solvents (e.g. o-dichlo-
robenzene and n-butyl alcohol) but also in a series of mono or-
ganic solvent systems such as dichloromethane (DCM), chloro-
form, tetrahydrofuran (THF), methanol, ethanol, acetonitrile
(MeCN), and dimethylacetamide (DMAc) etc. To the best of
our knowledge, this is a rare case of COF synthesis that exhibits
such excellent solvent adaptability. Besides, the reported Py-Py
COF5c which has similar structure with Py-COF was synthe-
sized as a counterpart by the conventional co-condensation ap-
proach. By comparison of the PXRD patterns and surface areas,
RESULTS AND DISCUSSION
Synthesis and Characterization. As shown in Scheme S1,
BFBAPy was prepared via a facile three-step route in high yield
and unambiguously characterized by NMR, MALDI-TOF MS
and single crystal X-ray diffraction analysis (Figure S16). In a
typical synthetic procedure of Py-COFs (Figure S22), BFBAPy
(29.6 mg, 0.05 mmol) was suspended in a mixture of organic
solvent (2 mL) and 6 M acetic acid (0.2 mL) followed by re-
fluxing for 72 h to afford orange crystalline solids (denoted as
Py-COFsolvent) in high yields. Fourier transform infrared (FT-IR)
spectra of Py-COFDCM and the monomer BFBAPy were com-
pared in Figure S1. The disappearance of N-H (~3470 and 3360
cm-1) vibration, dramatically attenuation of C=O (1680 cm-1)
stretching bands and the appearance of new intensive imine
(C=N) band at 1628 cm-1 confirmed the high polycondensation
ACS Paragon Plus Environment

Page 3 of 7
Journal of the American Chemical Society
degree of Py-COF.14 All the IR spectra of Py-COFs synthesized
1
2
3
4
5
6
7
8
from different solvents are nearly identical (Figure S1b). The
formation of imine linkages was further verified by 13C solid-
state NMR spectroscopy, with an obvious characteristic peak at
156 ppm assignable to the carbon of C=N double bonds.14 Other
aromatic carbon signals can be properly assigned as well (Fig-
ure S2). Elemental analysis indicated that the C, H and N con-
tents of the COFs were in good agreement with the theoretical
values expected for an infinite 2D sheet.
Interestingly, Py-COFs prepared from varied solvents exhib-
ited significantly different morphologies as revealed by the
scanning electron microscopies (Figure S6). For example,
spherical, rodlike, and platelike aggregates composed of small
nanoparticles (Figure S6c, S6d) or nanoflakes (Figure S6a, S6e,
S6h) were observed. These differences were probably caused
by the solvent polarity variation as reported before.16a Transmis-
sion electron micros-copy proved a nearly uniform porous tex-
ture (Figure S7).
Crystalline Structure. The crystallinity of Py-COFs syn-
thesized from different solvents was examined by powder X-
ray diffraction (PXRD) measurements. Actually, all the Py-
COFs exhibited strong diffraction peaks at 5.02o, 7.04o, 10.18o,
11.19o, 15.28o, 22.75o (Figure S4), which could be indexed to
(110), (020), (220), (040), (240) and (001) facets, respectively.
The first dominant diffraction peak at 5.02o corresponded to the
d-spacing of 1.70 nm, which was in good agreement with the
calculated length of the tetragon (1.59 nm, Figure 1a). The
PXRD pattern of Py-COFDCM was selected as the representative
experimental data to simulate the lattice packing model. As
shown in Figure 1b, the calculated PXRD pattern of AA stack-
ing model (purple) was in accordance with the experimental
ones (black), whereas the staggered AB stacking pattern (dark
yellow) exhibits significant difference from the experimental
PXRD data. Furthermore, the profile of Pawley refinement
matched well with the observed signals as evident by their neg-
ligible deviation (green) (Figure 1b) with the final Rwp and Rp
values converged to 5.57% and 4.16%, respectively. The Paw-
ley refinement afforded a P21 monoclinic space group with unit
cell parameters of a = 24.3740 Å, b = 26.2134 Å, c = 4.0287 Å,
α = γ = 90° and β = 72.1°.
Porosity of Py-COFs. The permanent porosity of Py-COFs
was assessed by N2 sorption measurements at 77 K (Figure 2a).
All the Py-COFs displayed reversible type I isotherms with
rapid N2 uptakes at the low relative pressure range P/P0 < 0.05,
characteristic of microporous materials.15 Brunauer–Emmett–
Teller (BET) surface areas calculated from the N2 adsorption
isotherms in the low pressure region revealed that all the Py-
COFs exhibited high specific surface areas (1200-1370 m2/g,
Figure S17) which are close to the theoretical value (1537 m2/g)
calculated by High-Throughput-based Complex Adsorption
and Diffusion Simulation Suite (HT-CADSS) according to the
literature method.15c The pore size distribution analysis of Py-
COFs based on the nonlocal density functional theory (NLDFT)
indicated one main distribution centered at the range of 1.20-
1.45 nm (Figure 2b), which is close to the theoretical value
(1.38 nm, Figure 1a).
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 2. (a) Nitrogen adsorption (solid) and desorption (open) iso-
therms at 77 K and (b) Pore size distribution curves based on
NLDFT calculation for Py-COFMeOH (black), Py-COFDCM (red),
Py-COFDMAc (blue), Py-COFEtOH (dark yellow), Py-COFTHF (wine)
and Py-COFo-DCB/n-BuOH (purple).
Stability of Py-COFs. The chemical stability of Py-
COFDCM was further examined by keeping the samples un-
der boiling water, aqueous NaOH (12 M) and HCl (12 M)
solutions for 3 days. All the samples retained their crystal-
linity, porosity and chemical constitution upon treatments
in these harsh conditions. For example, after the treatments,
the PXRD patterns (Figure S9a), surface areas (Figure S9b)
and FT-IR spectra (Figure S10) remained unchanged. In-
terestingly, crystalline Py-COF can also be obtained in 6 M
AcOH and 12 M HCl without adding any organic solvents
(denoted as Py-COF6M AcOH and Py-COF12M HCl, Figure S24),
which indicates Py-COF can also be formed and survived
in those harsh conditions. These control experiments rea-
sonably corroborate the extraordinary chemical stability of
Py-COF in strong acidic condition. Furthermore, the high
hydrophobicity (Figure S23) might also contribute to the
high stability of Py-COFDCM toward strong acid and base,
which protecting Py-COFDCM from hydrolysis16b and re-
mains their high crystallinity (Figure S4). On the other
hand, the thermogravimetric analysis (TGA) result indi-
o
cated that Py-COFDCM was thermally stable up to 400 C,
o
and displayed only 25% weight loss even heated at 800 C
(Figure S3). Such superior stabilities render Py-COFs to be
good candidates for potential applications in catalysis,3d
environmental remediation,4 and energy storage related ar-
eas.7
Monitoring of Py-COF Formation Process. To shed
more insights into the growth of Py-COFs, time-dependent
condensations were conducted in CH2Cl2 for monitoring
the evolution of the porous crystalline network. The con-
densation reactions were thus carried out at 0.5, 1, 2, 5, 9,
15, and 24 h. PXRD measurements were utilized to moni-
tor their crystallinity. As shown in Figure 3a, the charac-
teristic peak (2 = 5.02°) for Py-COFs became visible after
0.5 h and increased to be distinctive at ca. 1 h. With further
elongation of reaction time, the characteristic peak of Py-
COF became dominant while the diffraction peak for the
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 4 of 7
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 3. PXRD patterns of Py-COFDCM at different reaction times:
(a) 0~5 h; (b) 5~24 h.
Figure 4. (a) Photograph and grazing incidence XRD (GI-XRD)
patterns of Py-COF films grown on different substrates (3.75
mg/mL) with an incidence angle of 0.2o. (b) Optical images of Py-
COF films obtained in varied monomer concentrations on glass. (c)
SEM image of Py-COF film grown on glass; (d) AFM images of
Py-COF thin film (3.75 mg/mL).
monomer BFBAPy (2= 7.90°) exhibited dramatic attenua-
tions (0~5 h) and completely disappeared after ca. 9 h (Figure
3b). A highly crystalline Py-COF sample can be obtained after
24 h (Figure 3b) and the intensity of diffraction peak did not
exhibit further enhancement after 36 hours (Figure S14). Unlike
the rapid formation of crystalline boronate ester COFs at the
nucleation stage (within minutes),12 the growth of Py-COFs
were consistent with most reported imine-based COFs, which
involved an initial rapid precipitation of amorphous polymer
network (ca. 0-0.5 h) followed by gradual amorphous-to-crys-
talline transformation step (0.5-24 h).17 Furthermore, highly
crystalline Py-COFs can be synthesized under different atmos-
pheres and at relative low concentrations (Figure S11-S13),
which greatly simplified the synthetic procedure.
Meanwhile, the impact of stoichiometric imbalance on Py-
COF was also explored.17d The intensity of Py-COF exhibited
obvious decrement while the full width at half maximum
(FWHM) of the (100) diffraction peak at 5.02o showcased grad-
ual increase when different amounts (5%, 10%, 25% and 50%)
of 1,3,6,8-tetrakis(4-aminophenyl)pyrene (Py(NH2)4) were
added in Py-COFDCM reaction system. The surface areas of
these controlled samples also exhibited distinct decrease (Fig-
ure S33c). These results jointly indicated that the more
Py(NH2)4 was added, the worse the crystallinity was (Figure
S33a). The similar tendency was observed when different
amounts of aniline modulator14 were added to the reaction sys-
tem (Figures S33b, S33d). These observations are different
from the previous reported examples using co-condensation
strategy where the addition of modulator and the stoichiometric
imbalance did greatly improved the crystallinity of the resultant
COFs.10f,17d,18 Thus, in our current cases, the stoichiometric im-
balance might be insensitive to the crystallinity of the COFs be-
cause both functional moieties either are or are not soluble in
different reaction conditions, and it became easier to find suita-
ble conditions that work for COFs formation in this “two-in-
one” systems that leads to the good solvent adaptability.
Py-COF powder (Figure 4a). UV-vis absorption spectra of
Py-COF film and powder were compared with that of the
monomer in Figure S8. Both of them exhibited intensive
light absorption in the visible light region. The absorption
onset of Py-COF powder and film were 552 and 557 nm,
which displayed a slight red shift compared with that of
BFBAPy (544 nm). SEM images of the transparent Py-
COF film on glass indicated the thin films were continuous
and composed of evenly distributed crystalline particles up
to ca. 500 nm in size (Figure 4c). AFM images of the Py-
COF thin film (3.75 mg/mL) revealed a thickness of 105
nm (Figure 4d) with root-mean-square (RMS) roughness
of 10.14 nm (Figure S19). The orientation of Py-COF film
was investigated by 2D synchrotron radiation grazing inci-
dence wide-angle X-ray scattering (2D-GIWAXS). The
ring-like scattering pattern indicated Py-COF film exhib-
ited almost no preferred orientation (Figure S32). The film
thickness could be readily tuned (Figure S18) by control-
ling the “initial concentration” of the monomer, which can
be recognized by the naked eyes (Figure 4b). Compared
with other reported COF films,19-20 the current Py-COF
films exhibit better substrate adaptability (Figure 4a), less
solvent dependence (Figure S20) and better transparency
(Figure S21). And such solvent adaptability for Py-COF
synthesis make it possible to grow high quality film on ITO
substrate with PEDOT/PSS coating (Figure S26). These
features would greatly facilitate their potential applications
in optoelectronics.21 For example, a preliminary trial of
such film applied as the hole transporting layers in perov-
skite solar cell22 was demonstrated. As shown in Figure 5,
the device based on the mixed perovskite
Growth and Characterization of Py-COF Films.
COFs are usually obtained as insoluble powders, which hamper
their practical applications to some extent, especially for elec-
tronic devices. Recently, oriented COF thin films have been de-
veloped and served as active materials in optoelectronic de-
vices19 and photoelectrodes for water splitting.20 These studies
prompted us to grow Py-COF thin films using our bifunctional
monomer BFBAPy on various substrates such as glass, ITO
substrate and silicon wafer. The successful growth of highly
crystalline Py-COF films on these substrates was proved by
their appearance of strong diffraction peaks at 5.02o as that of
(FA0.85MA0.15Pb(I0.85Br0.15)3)22b
that
comprising
formamidine lead iodide (FAPbI3, 85%) and methylammo-
nium lead bromide (MAPbBr3, 15%) showed an open-cir-
cuit voltage (Voc) of 0.76 V, a short-circuit current (Jsc) of
15.38 mA/cm2, and a filled factor (FF) of 54.33%, which
resulted in a power conversion efficiency (PCE) of
6.36%.22c The performance of the resulting device is mod-
erate (Table S6); this experiment is a proof-of-concept
demonstration of using transparent COF thin films for op-
toelectronics. Improved photoenergy conversion efficiency
ACS Paragon Plus Environment

Page 5 of 7
Journal of the American Chemical Society
would be achievable when more matched energy gaps, bet-
1
2
ter interfacial quality, and large-area-oriented COFs films
with less grain boundaries are available.
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 5. (a) The schematic illustration of the device (with an
exposed active area of 0.03 cm2) fabrication process; (b) the device
architecture; and (c) current density-voltage (J-V) characteristic
curve under AM 1.5G 100 mW cm−2 simulated solar light by
utilizing Py-COF film as the hole transporting layer in perovskite
solar cell.
Versatility of the Two-in-One Strategy. In order to illus-
trate the generality and tolerance of the two-in-one strategy, an-
other two bifunctional monomers, 1,4-bis(4-formylphenyl)-2,5-
bis((4-aminophenyl)ethynyl)) benzene (BFBAEB) and 1,6-
bis(4-formylphenyl)-3,8-bis((4-aminophenyl)ethynyl))pyrene
(BFBAEPy) (Figure 6a), were designed and synthesized to con-
struct two new COFs. As expected, two corresponding crystal-
line COFs were facilely synthesized in at least three different
simplex organic solvents (Figure S27). The PXRD pattern of
BFBAEB-COF displays strong diffraction at 2.95o, 5.94o, 8.93o,
11.95o, 14.97o and 24.07o, which could be assigned to (100),
(200), (300), (400), (500) and (001) facets. Similarly, the dif-
fraction peaks for BFBAEPy-COF appear at 2.54o, 4.55o, 5.30o,
6.97o, 9.29o, 24.00o, which were ascribed to the (100), (110),
(200), (210), (310), and (001) diffractions. It is noteworthy that
both the experimental PXRD results coincide well with the sim-
ulated hexagonal AA-stacking models (Figures 6b-6c), which
is different from the Py-COF (orthorhombic structure). The de-
tails of structural simulation were summarized in Figures S28-
S29 and Tables S4-S5. The chemical constitution and porosity
of the two COFs were further confirmed by FI-IR and N2 sorp-
tion isotherms (Figures S30 and S31). Interestingly, these two
COFs built from the bifunctional monomers (BFBAEB and
BFBAEPy) with different substituted arm length preferred to
form heteroporous COFs with dual pores, which were demon-
strated by both the PXRD results and the pore size distribution
analysis (Figure S31). It is noteworthy that these two dual-pore
COFs with Kagome structures cannot be formed by co-conden-
sation of corresponding building blocks (Schemes S9 and S10)
which were also demonstrated by the control experiments. For
example, the co-condensation of TEAB and TFPB failed to give
any crystalline COF upon ten different condition screening
(Figure S35). On the other hand, the co-condensation of TAEPy
and Py(CHO)4 afforded TAEPy-COF only in specific solvent
combinations (Figure S36) but resulted in a single pore rhombic
structure (Figure S37). These results further confirm the ration-
ality and feasibility of our two-in-one molecular design strategy
for new COF synthesis.
Figure 6. (a) Self-condensation of two new bifunctional monomers
BFBAEB and BFBAEPy to obtained the corresponding COFs. Ex-
perimental PXRD patterns (black), Pawley refinement (purple),
their difference (green), simulated profiles using AA-stacking (red)
and AB-stacking (blue) modes for (b) BFBAEB-COF and (c)
BFBAEPy-COF.
CONCLUSION
In summary, we successfully developed a two-in-one molecular
design strategy to construct 2D imine COFs in easy and versa-
tile conditions. The use of single organic solvent as the reaction
media greatly facilitates the preparation of COFs. Furthermore,
it is readily to grow continuous Py-COF thin films in high qual-
ity on various substrates based on the “two-in-one” monomer.
This strategy is also demonstrated to be applicable for other two
COFs synthesis with different building blocks. Moreover, it
could also be extended to different synthetic techniques like
chemical vapor deposition23a and interface-assisted synthesis23b
of molecular frameworks. Although more synthetic efforts is
needed for obtaining the elaborately designed bifunctional
monomers, it is worthwhile considering the merits mentioned
above. The utilization of the “two-in-one” approach to construct
crystalline COFs based on a series of new building blocks
and/or new linkages is currently undergoing in our laboratory.
ASSOCIATED CONTENT
Supporting Information
Experiment details and characterization of the monomer and Py-
COFs. This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 6 of 7
Chem. Soc., 2017 139, 4513−4520. (b) Zhang, G.; Li, X.; Liao, Q.; Liu, Y.;
*E-mail: long.chen@tju.edu.cn (L. Chen).
Xi, K.; Huang, W.; Jia, X. Water-Dispersible PEG-Curcumin/Amine-
Functionalized Covalent Organic Framework Nanocomposites as Smart
Carriers for in Vivo Drug Delivery. Nat. Commun. 2018, 9, 2785.
(7) (a) DeBlase, C. R.; Silberstein, K. E.; Truong, T-T.; Abruña, H. D.;
Dichtel, W. R. β-Ketoenamine-Linked Covalent Organic Frameworks
Capable of Pseudocapacitive Energy Storage. J. Am. Chem. Soc. 2013, 135,
16821−16824. (b) Halder, A.; Ghosh, M.; Khayum M, A.; Bera, S.;
Addicoat, M.; Sasmal, H. S.; Karak, S.; Kurungot, S.; Banerjee, R.
Interlayer Hydrogen-Bonded Covalent Organic Frameworks as High-
Performance Supercapacitors. J. Am. Chem. Soc. 2018, 140, 10941−10945.
(c) DeBlase, C. R.; Hernández-Burgos, K.; Silberstein, K. E.; Rodríguez-
Calero, G. G.; Bisbey, R. P.; Abruña, H. D.; Dichtel, W. R. Rapid and
Efficient Redox Processes within 2D Covalent Organic Framework Thin
Films. ACS Nano 2015, 9, 3178-3183. (d) Vazquez-Molina, D. A.;
Mohammad-Pour, G. S.; Lee, C.; Logan, M. W.; Duan, X.; Harper, J. K.;
Uribe-Romo, F. J. Mechanically Shaped Two-dimensional Covalent
Organic Frameworks Reveal Crystallographic Alignment and Fast Li-Ion
Conductivity. J. Am. Chem. Soc. 2016, 138, 9767-9770.
(8) (a) Calik, M.; Auras, F.; Salonen, L. M.; Bader, K.; Grill, I.;
Handloser, M.; Medina, D. D.; Dogru, M.; Löbermann, F.; Trauner, D.;
Hartschuh, A.; Bein, T. Extraction of Photogenerated Electrons and Holes
from a Covalent Organic Framework Integrated Heterojunction. J. Am.
Chem. Soc. 2014, 136, 17802−17807. (b) Lin, C.-Y.; Zhang, D.; Zhao, Z.;
Xia, Z. Covalent Organic Framework Electrocatalysts for Clean Energy
Conversion. Adv. Mater. 2018, 30, 1703646.
(9) (a) Matsumoto, M.; Dasari, R. R.; Ji, W.; Feriante, C. H.; Parker, S.
Marder, T. C.; Dichtel, W. R. Rapid, Low Temperature Formation of Imine-
Linked Covalent Organic Frameworks Catalyzed by Metal Triflates.
J. Am. Chem. Soc. 2017, 139, 4999-5002. (b) Karak, S.; Kumar, S.; Pachfule,
P.; Banerjee, R. Porosity Prediction through Hydrogen Bonding in Covalent
Organic Frameworks. J. Am. Chem. Soc. 2018, 140, 5138−5145. (c) Biswal,
B. P.; Chandra, S.; Kandambeth, S.; Lukose, B.; Heine, T.; Banerjee, R.
Mechanochemical Synthesis of Chemically Stable Isoreticular Covalent
Organic Frameworks. J. Am. Chem. Soc. 2013, 135, 5328−5331.
(10) (a) Huang, N.; Zhai, L.; Coupry, D. E.; Addicoat, M. A.; Okushita,
K.; Nishimura, K.; Heine, T.; Jiang, D. Multiple-Component Covalent
Organic Frameworks. Nat. Commun. 2016, 7, 12325. (b) Liang, R.-R.; Xu,
S.-Q.; Pang, Z.-F.; Qi, Q.-Y.; Zhao, X. Self-Sorted Pore-Formation in the
Construction of Heteropore Covalent Organic Frameworks Based on
Orthogonal Reactions. Chem. Commun. 2018, 54, 880−883. (c) Pang, Z.-F.;
Xu, S.-Q.; Zhou, T.-Y.; Liang, R.-R.; Zhan, T.-G.; Zhao, X. Construction
of Covalent Organic Frameworks Bearing Three Different Kinds of Pores
through the Heterostructural Mixed Linker Strategy. J. Am. Chem. Soc.
2016, 138, 4710−4713. (d) Zeng, Y.; Zou, R.; Zhang, H.; Yao, X.; Ma, X.;
Zou, R.; Zhao, Y. Covalent Organic Frameworks Formed with Two Types
of Covalent Bonds Based on Orthogonal Reactions. J Am. Chem. Soc. 2015,
137, 1020−1023. (e) Jin, Y.; Hu, Y.; Zhang, W. Tessellated Multiporous
Two-dimensional Covalent Organic Frameworks. Nat. Rev. Chem. 2017, 1,
0056. (f) Waller, P. J.; Lyle, S. J.; Osborn Popp, T. M.; Diercks, C. S.;
Reimer, J. A.; Yaghi, O. M. Chemical Conversion of Linkages in Covalent
Organic Frameworks. J. Am. Chem. Soc. 2016, 138, 15519−15522.
(11) Kuhn, P.; Antonietti, M.; Thomas, A. Porous, Covalent Triazine-
Based Frameworks Prepared by Ionothermal Synthesis. Angew. Chem. Int.
Ed. 2008, 47, 3450−3453.
(12) (a) Smith, B. J.; Dichtel, W. R. Mechanistic Studies of Two-
Dimensional Covalent Organic Frameworks Rapidly Polymerized from
Initially Homogenous Conditions. J. Am. Chem. Soc., 2014, 136, 8783-8789.
(b) Smith, B. J.; Hwang, N.; Chavez, A. D.; Novotney, J. L.; Dichtel, W. R.
Growth Rates and Water Stability of 2D Boronate Ester Covalent Organic
Frameworks. Chem. Commun. 2015, 51, 7532−7535.
(13) Sun, Q.; Aguila, B.; Perman, J.; Butts, T.; Xiao, F.-S.; Ma, S.
Integrating Superwettability within Covalent Organic Frameworks for
Functional Coating. Chem. 2018, 4, 1726−1739.
1
2
3
4
5
6
7
8
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENT
This work was financially supported by the National Key Research
and Development Program of China (2017YFA0207500) and the
Natural Science Foundation of Tianjin (17JCJQJC44600). We
thank Prof. Dong Wang at Institute of Chemistry, Chinese Acad-
emy of Sciences for his kind help on the measurement of 2D-
GIWAXS.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
REFERENCES
(1) (a) Cꢀtꢁ, A. P.; Benin, A. I.; Ockwig, N. W.; O’Keeffe, M.; Matzger,
A. J.; Yaghi, O. M. Porous, Crystalline, Covalent Organic Frameworks. Sci-
ence 2005, 310, 1166−1170. (b) Diercks, C. S.; Yaghi, O. M. The atom, the
Molecule, and the Covalent Organic Framework. Science 2017, 355, 923.
(c) Huang, N.; Wang, P.; Jiang, D. Covalent Organic Frameworks: A Ma-
terials Platform for Structural and Functional Designs. Nat. Rev. Mater.
2016, 1, 16068. (d) Song, Y.; Sun, Q.; Aguila, B.; Ma, S. Opportunities of
Covalent Organic Frameworks for Advanced Applications Adv. Sci. 2018,
5, 1801410. (e) Auras, F.; Ascherl, L.; Hakimioun, A. H.; Margraf, J. T.;
Hanusch, F. C.; Reuter, S.; Bessinger, D.; Dꢂblinger, M.; Hettstedt, C.; Ka-
raghiosoff, K.; Herbert, S.; Knochel, P.; Clark, T.; Bein, T. Synchronized
Offset Stacking: A Concept for Growing Large-Domain and Highly Crys-
talline 2D Covalent Organic Frameworks. J. Am. Chem. Soc. 2016, 138,
16703-16710. (f) Ascherl, L.; Sick, T.; Margraf, J. T.; Lapidus, S. H.; Calik,
M.; Hettstedt, C.; Karaghiosoff, K.; Dꢂblinger, M.; Clark, T.; Chapman, K.
W.; Auras, F.; Bein, T. Molecular Docking Sites Designed for the Genera-
tion of Highly Crystalline Covalent Organic Frameworks. Nat. Chem. 2016,
8, 310-316.
(2) (a) Huang, N.; Krishna, R.; Jiang, D. Tailor-Made Pore Surface En-
gineering in Covalent Organic Frameworks: Systematic Functionalization
for Performance Screening. J. Am. Chem. Soc. 2015, 137, 7079−7082. (b)
Furukawa, H.; Yaghi, O. M. Storage of Hydrogen, Methane, and Carbon
Dioxide in Highly Porous Covalent Organic Frameworks for Clean Energy
Applications. J. Am. Chem. Soc. 2009, 131, 8875−8883. (c) Zeng, Y.; Zou,
R.; Zhao, Y. Covalent Organic Frameworks for CO2 Capture. Adv. Mater.
2016, 28, 2855−2873. (d) Fan, H.; Mundstock, A.; Feldhoff, A.; Knebel, A.;
Gu, J.; Meng, H.; Caro, J. Covalent Organic Framework-Covalent Organic
Framework Bilayer Membranes for Highly Selective Gas Separation. J. Am.
Chem. Soc. 2018, 140, 10094−10098.
(3) (a) Ding, S.-Y.; Gao, J.; Wang, Q.; Zhang, Y.; Song, W.-G.; Su, C.-
Y.; Wang, W. Construction of Covalent Organic Framework for Catalysis:
Pd/COF-LZU1 in Suzuki-Miyaura Coupling Reaction. J. Am. Chem. Soc.
2011, 133, 19816−19822. (b) Lin, S.; Diercks, C. S.; Zhang, Y.-B.;
Kornienko, N.; Nichols, E. M.; Zhao, Y.; Pairs, A. R.; Kim, D.; Yang, P.;
Yaghi, O. M. Covalent Organic Frameworks Comprising Cobalt Porphyrins
for Catalytic CO2 Reduction in Water. Science 2015, 349, 1208−1213. (c)
Sun, Q.; Aguila, B.; Perman, J. A.; Nguyen, N. T.-K.; Ma, S. Flexibility
Matters: Cooperative Active Sites in Covalent Organic Framework and
Threaded Ionic Polymer. J. Am. Chem. Soc. 2016, 138, 15790−15796.
(4) (a) Sun, Q.; Aguila, B.; Earl, L. D.; Abney, C. W.; Wojtas, L.;
Thallapally, P. K.; Ma, S. Covalent Organic Frameworks as a Decorating
Platform for Utilization and Affinity Enhancement of Chelating Sites for
Radionuclide Sequestration. Adv. Mater. 2018, 1705479. (b) Ji, W.; Xiao,
L.; Ling, Y.; Ching, C.; Matsumoto, M.; Bisbey, R. P.; Helbling, D. E.;
Dichtel, W. R. Removal of GenX and Perfluorinated Alkyl Substances from
Water by Amine-Functionalized Covalent Organic Frameworks. J. Am.
Chem. Soc. 2018, 140, 12677−12681.
(5) (a) Lin, G.; Ding, H.; Yuan, D.; Wang, B.; Wang, C. A Pyrene-Based,
Fluorescent Three-Dimensional Covalent Organic Framework. J. Am.
Chem. Soc. 2016, 138, 3302−3305. (b) Hao, Q.; Zhao, C.; Sun, B.; Lu, C.;
Liu, J.; Liu, M.; Wan, L.-J.; Wang, D. Confined Synthesis of Two-
Dimensional Covalent Organic Framework Thin Films within
Superspreading Water Layer. J. Am. Chem. Soc., 2018 140, 12152-12158.
(c) Ascherl, L., Evans, E. W., Hennemann, M., Nuzzo, D. D., Hufnagel, A.
G., Beetz, M., Friend, R. H., Clark, T., Bein, T., Auras, F. Solvatochromic
Covalent Organic Frameworks. Nat. Commun. 2018, 9, 3802.
(14) Uribe-Romo, F. J.; Hunt, J. R.; Furukawa, H.; Klöck, O’Keeffe, M.;
Yaghi, O. M. A Crystalline Imine-Linked 3-D Porous Covalent Organic
Framework. J. Am. Chem. Soc. 2009, 131, 4570−4571.
(15) (a) Weber, J.; Antonietti, M.; Thomas, A. Microporous Networks of
High-Performance Polymers: Elastic Deformations and Gas Sorption
Properties. Macromolecules 2008, 41, 2880−2885. (b) Thommes, M.;
Kaneko, K.; Neimark, A. V.; Olivier, J. P.; Rodriguez-Reinoso, F.;
Rouquerol, J.; Sing, K. S. W. Physisorption of Gases, with Special
Reference to the Evaluation of Surface Area and Pore Size Distribution.
Pure Appl. Chem. 2015; 87, 1051−1069. (c) Yang, Q.; Liu, D.; Zhong, C.;
Li, J.-R. Development of Computational Methodologies for Metal−Organic
(6) (a) Mitra, S.; Sasmal, H. S.; Kundu, T.; Kandambeth, S.; Illath, K.;
Díaz Díaz, D.; Banerjee, R. Targeted Drug Delivery in Covalent Organic
Nanosheets (CONs) via Sequential Postsynthetic Modification. J. Am.
ACS Paragon Plus Environment

Page 7 of 7
Journal of the American Chemical Society
Frameworks and Their Application in Gas Separations. Chem. Rev. 2013,
113, 8261−8323.
Extrinsic Proton Conductivities in Covalent Organic Frameworks. Chem.
Mater. 2016, 28, 1489–1494. (c) Dogru, M.; Handloser, M.; Auras, F.;
1
2
3
4
5
6
7
8
(16) (a) Das, G.; Skorjanc, T.; Sharma, S. K.; Gándara, F.; Lusi, M.; Rao,
D. S. S.; Vimala, S.; Prasad, S. K.; Raya, J.; Han, D. S.; Jagannathan, R.;
Olsen, J.-C.; Trabolsi, A. Viologen-Based Conjugated Covalent Organic
Networks via Zincke Reaction. J. Am. Chem. Soc. 2017, 139, 9558−9565.
(b) Kandambeth, S.; Mallick, A.; Lukose, B.; Mane, M. V.; Heine, T.;
Banerjee, R. Construction of Crystalline 2D Covalent Organic Frameworks
Kunz, T.; Medina, D.; Hartschuh, A.; Knochel, P.; Bein, T. A
Photoconductive Thienothiophene-Based Covalent Organic Framework
Showing Charge Transfer Towards Included Fullerene. Angew. Chem. Int.
Ed. 2013, 52, 2920−2924.
(20) (a) Sick, T.; Hufnagel, A. G.; Kampmann, J.; Kondofersky, I.; Calik,
M.; Rotter, J. M.; Evans, A.; Döblinger, M.; Herbert, S.; Peters, K.; Böhm,
D.; Knochel, P.; Medina, D. D.; Fattakhova-Rohlfing, D.; Bein, T. Oriented
Films of Conjugated 2D Covalent Organic Frameworks as Photocathodes
for Water Splitting. J. Am. Chem. Soc. 2018, 140, 2085−2092. (b) Vyas, V.
S.; Haase, F.; Stegbauer, L.; Savasci, G.; Podjaski, F.; Ochsenfeld, C.;
Lotsch, B. V. A Tunable Azine Covalent Organic Framework Platform for
Visible Light-Induced Hydrogen Generation. Nat. Commun. 2015, 6, 8508.
(21) Lohse, M. S.; Bein, T. Covalent Organic Frameworks: Structures,
Synthesis, and Applications. Adv. Funct. Mater. 2018, 28, 1705553.
(22) (a) Green, M. A.; Ho-Baillie, A.; Snaith, H. J. The Emergence of
Perovskite Solar Cells. Nature Photon. 2014, 8, 506−514. (b) Bu, T.; Liu,
X.; Chen, R.; Liu, Z.; Li, K.; Li, W.; Peng, Y.; Ku, Z.; Huang, F.; Cheng, J.
Zhong, Y.-B. Organic/Inorganic Self-doping Controlled Crystallization and
Electronic Properties of Mixed Perovskite Solar Cells. J. Mater. Chem. A
2018, 6, 6319-6326. (c) Wu, C.; Liu, Y.; Liu, H.; Duan, C.; Pan, Q.; Zhu,
J.; Hu, F.; Ma, X.; Jiu, T.; Li, Z.; Zhao, Y. Highly Conjugated Three-
Dimensional Covalent Organic Frameworks Based on Spirobifluorene for
Perovskite Solar Cell Enhancement. J. Am. Chem. Soc. 2018, 140,
10016−10024.
with Remarkable Chemical (Acid/Base) Stability via
a Combined
Reversible and Irreversible Route. J. Am. Chem. Soc. 2012, 134,
19524−19527.
(17) (a) Smith, B. J.; Overholts, A. C.; Hwang, N.; Dichtel, W. R. Insight
into The Crystallization of Amorphous Imine-Linked Polymer Networks to
2D Covalent Organic Frameworks. Chem. Commun. 2016, 52, 3690−3693.
(b) Gao, Q.; Bai, L.; Zeng, Y.; Wang, P.; Zhang, X.; Zou, R.; Zhao, Y.
Reconstruction of Covalent Organic Frameworks by Dynamic Equilibrium.
Chem. Eur. J. 2015, 21, 16818−16822. (c) Yuan, Y.-C.; Sun, B.; Cao, A.-
M.; Wang, D.; Wan, L.-J. Heterogeneous Nucleation and Growth of Highly
Crystalline Imine-Linked Covalent Organic Frameworks. Chem. Commun.
2018, 54, 5976−5979. (d) Calik, M.; Sick, T.; Dogru, M.; Döblinger, M.;
Datz, S.; Budde, H.; Hartschuh, A.; Auras, F.; Bein, T. From Highly
Crystalline to Outer Surface-Functionalized Covalent Organic Frameworks :
A Modulation Approach. J. Am. Chem. Soc. 2016, 138, 1234-1239.
(18) Ma, T.; Kapustin, E. A.; Yin, S. X.; Liang, L.; Zhou, Z.; Niu, J.; Li,
L.-H.; Wang, Y.; Su, J.; Li, J.; Wang, W. D.; Wang, W.; Sun, J.; Yaghi, O.
M. Single-crystal x-ray diffraction structures of covalent organic
frameworks. Science 2018, 361, 48-52.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(23) (a) Stassen, I; Styles, M.; Grenci, G.; Van Gorp, H.; Vanderlinden,
W.; De Feyter, S.; Falcaro, P.; De Vos, D.; Vereecken, P.; Ameloot, R.
Chemical Vapour Deposition of Zeolitic Imidazolate Framework Thin
Films. Nat. Mater. 2016, 15, 304−310. (b) Dong, R.; Zhang, T.; Feng, X.
Interface-Assisted Synthesis of 2D Materials: Trend and Challenges. Chem.
Rev. 2018, 118, 6189−6235.
(19) (a) Colson, J. W.; Woll, A. R.; Mukherjee, A.; Levevdorf, M. P,;
Spitler, E. L.; Shields, V. B.; Spencer, M. G.; Park, J.; Dichtel, W. R.
Oriented 2D Covalent Organic Framework Thin Films on Single-Layer
Graphene. Science 2011, 332, 228−231. (b) Chandra, S.; Kundu, T.; Dey,
K.; Addicoat, M.; Heine, T.; Banerjee, R. Interplaying Intrinsic and
Insert Table of Contents artwork here
ACS Paragon Plus Environment